electronics Article
SINDVis: User-Centered Dynamic Interactive Visualization System for Space Information Networks Shaobo Yu 1 , Lingda Wu 1, *, Xitao Zhang 1 , Xiangli Meng 1 and Pengrui Cen 2 1 2
*
Science and Technology on Complex Electronic System Simulation Laboratory, Space Engineering University, Beijing 101416, China;
[email protected] (S.Y.);
[email protected] (X.Z.);
[email protected] (X.M.) Institute of Beijing Remote Sensing Information, Beijing 100192, China;
[email protected] Correspondence:
[email protected]; Tel.: +86-10-6636-4329
Received: 29 September 2018; Accepted: 8 November 2018; Published: 12 November 2018
Abstract: As an important national strategy infrastructure, the Space Information Network (SIN) is a powerful platform for future information support. In this paper, we design and implement a user-centered, dynamic, interactive visualization system (SINDVis), and aim to assist multi-class users to understand, build, develop, maintain, and manage the SIN. We introduce the concept and architecture of SIN, summarize the key technologies of dynamic visualization and visual analysis, and analyze the basic characteristics of three types of users. Combining the content above, we design the architecture of SINDVis from an input module, a core-processing module, an output module, and a user body. We also describe eight basic functions of the entity domain view (GeoView) and topology domain view (TopolView). Meanwhile, we analyze the implementation methods of the GeoView and TopolView, including an improved Force-Directed Algorithm (FDA) layout, Fusion of Animation and Timeline (FAT) visualization, and Panning and Zooming (P&Z) interactions. We analyze the experiment platforms and running environments of the GeoView and TopolView and realize the main contents of both views with a typical SIN. The results also verify the validity and feasibility of the theories and methods proposed. Finally, we discuss and analyze experimental results and the advantages and disadvantages of the SINDVis and look forward to future work. With the development of visualization and visual analysis technology, both application-driven and user-interaction features are gradually highlighted. We introduce the visualization technology into the field of SIN in order to provide new ideas for the basic theory and key technology research of SIN. Keywords: space information networks; dynamic graph; information visualization; user-centered; interactive visual analysis; Force-Directed; animation and timeline
1. Introduction There are multiple types of network systems in human and virtual societies [1], such as communication networks, social networks, urban transportation networks, cooperation networks, trade networks, and command and control networks, etc. In fact, regardless of people’s livelihood needs, or military applications, most human beings are currently greatly dependent on networks. With the rapid development of science and technology, aerospace has gradually become the focus of many countries, especially in terms of the modernized armament game. The space information network (SIN) [2] plays an extremely important role in this game, and the major aerospace countries of the world are actively exploring and conducting related research [3]. As a huge, complex network system, the SIN has some typical characteristics, such as complexity, heterogeneity, and heterogeneity as well as being limited, multilayer and, most obviously, dynamic [4]. The dynamic characteristic of SIN can be subdivided into time-varying aspects in the time domain and space-varying aspects in the space domain. For SIN, because the time-varying and space-varying Electronics 2018, 7, 316; doi:10.3390/electronics7110316
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characteristics are simultaneously present, the irregularity and instability of the network topology is greatly increased, and this also brings many challenges to the construction, management, and use of SIN. In recent years, with the support of the National Natural Science Foundation of China, scholars have made many research achievements regarding the top-level design of SIN architecture, the theories and methods of high-speed transmission, and the sparse representation and fusion processing of space information [5]. However, through a comparative analysis, we identified that the following problems still need to be solved. Question 1. Although there are some technical schemes for SIN architecture, there is no effective demonstration system or integrated platform to show the concrete structure of SIN in the entity domain. As we know, there are a number of simulation platforms, such as the STK (Satellite Tool Kit) and SaVi. However, both of them are based on the client/server (C/S) architecture implementation, and the SaVi is mainly applied to academic verification. Therefore, the STK and SaVi are inconvenient for application and promotion. For multi-class users, it is very important to determine how to demonstrate effectively the composition structure and operation laws of the SIN in the entity domain. Question 2. With the increasing demand for the construction and development of SIN, its scale is expanding, and its composition structure is becoming more and more complex. For users who come from the department of construction and management of SIN, it is necessary to understand the system structure of SIN with scale enlargement. Meanwhile, we also need to understand the topology structure model of SIN and explore the key nodes and core links of the SIN. All of the above aspects are very important for maintaining normal operation and daily management. At present, there is no relevant molding platform to show the topology structure and demonstrate its topology evolution laws of SIN in the topology domain. For the above questions, we introduce some relevant techniques and methods of visualization, and design and implement a dynamic interactive system of SIN, named SINDVis. The system can satisfy multiple needs of multi-class users at the same time. The rest of the paper is organized as follows: In Section 2, we explain the related work, including the concepts and architecture of SIN, the technology principles of dynamic visualization and visual analysis, and multi-class users’ characteristics. In Section 3, we build the architecture of SINDVis, analyze the specific functions of the visual views of GeoView and TopolView, and discuss relevant theories and methods of realizing the above views. Section 4 presents the verification of the instances, and we use a typical SIN as an example for the implementation of GeoView and TopolView. Section 5 discusses the verification results. Section 6 concludes the paper. 2. Related Work The purpose of this section is to introduce the concepts and architecture of SIN, analyze the technology principles of dynamic visualization and visual analysis, and discuss multi-class users’ characteristics. 2.1. SIN Concept and Architecture Researchers have presented various interpretations for SIN [2–6]. Combined with the main research plan of the National Nature and Science Fund of China, “Space information networks based theory and key technology”, we define the concept of SIN as follows. Definition 1. SIN is an integrated information network system and network infrastructure that is carried by space platforms. It is composed of a satellite system (such as geostationary earth orbit (GEO) satellites, nonsynchronous medium earth orbit (MEO) satellites, nonsynchronous low earth orbit (LEO) satellites, mainly responsible for processing the load), other information systems HABs (Hot Air Balloons) or UAVs (Unmanned Aerial Vehicles) in near-space, or terminals (ground station, mainly responsible for control). It can support real-time data acquisition, transmission, and processing of mass data, and achieve systematic information service application through integrated network interconnecting. It provides integrated investigation, navigation,
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communications, and other services, and realizes battlefield situational awareness, such as communication Electronics 2018, 7, x FOR PEER REVIEW 3 of 25 broadcasting; investigation and surveillance; intelligence detection; navigation and positioning; missile warning; andElectronics weather,2018, hydrology, and terrain. 7, x FOR PEER REVIEW 3 of 25 communication broadcasting; investigation and surveillance; intelligence detection; navigation and positioning; missile warning; andof weather, hydrology, and terrain. communication broadcasting; investigation and surveillance; intelligence detection; navigation and By analyzing the structure its backbone network and other supporting facilities, we determined
missile warning; and weather, hydrology, terrain.and thepositioning; specific components SIN. According to its and function Definition 1, SIN should be mainly By analyzing the of structure of its backbone network and other supporting facilities, we composed of four layers: the GEO layer satellite system, the MEO/LEO layer satellite system, the Near determined the specific components of SIN. According to its function and Definition 1, SIN should By analyzing the structure of its backbone network and other supporting facilities, we be mainly composed of four layers: the GEO layer satellite system, the MEO/LEO layer satellite Space layer information system, and the Ground layer terminals. Each section will be discussed determined the specific components of SIN. According to its function and Definition 1, SIN should in system, thefollowing Near Space system, andsatellite the Ground layer terminals. Each section will detail in the text. be mainly composed oflayer four information layers: the GEO layer system, the MEO/LEO layer satellite be discussed in detail inlayer the following text.system, and the Ground layer terminals. Each section will system, the Near Space information
Definition 2. 2. (GEO Layer System). GEO is a special geosynchronous orbit with zero inclination with be discussed in detail inSatellite the following text. Definition (GEO Layer Satellite System). GEO is a special geosynchronous orbit with zero inclination with an an orbital height of 35786 km and the same orbital period as as thethe Earth’s rotation cycle. The satellite covering area orbital height of 35786 and the same orbital Earth’s rotation cycle. covering Definition 2. (GEO Layerkm Satellite System). GEO isperiod a special geosynchronous orbit withThe zerosatellite inclination with of the orbit is orbit large and static relativerelative to the ground, so it is playing increasingly important roles inroles the civil areaorbital of the and the ground, so the it isEarth’s playing increasingly in theand an height isoflarge 35786 kmstatic and the sametoorbital period as rotation cycle. important The satellite covering military fields, such as communication, navigation, warning, and meteorology. Therefore, in the SIN, we can civil of and as communication, and increasingly meteorology.important Therefore, roles in theinSIN, area themilitary orbit isfields, large such and static relative to thenavigation, ground, so warning, it is playing the relyweoncan at least three GEO satellites to achieve the construction of the GEO layer satellite system, and the system on at fields, least three GEO satellites to achieve the construction of the GEO layerTherefore, satellite system, and civil andrely military such as communication, navigation, warning, and meteorology. in the SIN, ◦ full-cycle coverage. The composition structure of the GEO layer satellite system is shown in canwe achieve 360 the system coverage. The composition structure of the GEO layer satellite system is can relycan on achieve at least 360° three full-cycle GEO satellites to achieve the construction of the GEO layer satellite system, and Figure 1. shown in Figure 1. the system can achieve 360° full-cycle coverage. The composition structure of the GEO layer satellite system is shown in Figure 1. GEO-1 GEO-1
GEO-2
GEO-3
GEO-2
GEO-3
GEO Layer GEO Layer
Figure Compositionstructure structureof ofthe the geostationary geostationary earth system. Figure 1. 1. Composition earthorbit orbit(GEO) (GEO)layer layersatellite satellite system. Figure 1. Composition structure of the geostationary earth orbit (GEO) layer satellite system.
Definition 3. (MEO/LEO Layer Satellite System). The MEO satellite orbital is 5000~20,000 km and the LEO Satellite System). Thekm. MEO satellite orbital is the 5000~20,000 km andexist the LEO Definition 3. (MEO/LEO satellite orbital is generallyLayer between 700 km and 1500 Thesatellite satellites serving MEO/LEO in Definition 3. (MEO/LEO Layer Satellite System). The MEO orbital is 5000~20,000 km layer and the LEO satellite orbital is generally between 700 km and 1500 km. The satellites serving the MEO/LEO layer exist in the the network form, and in thebetween SIN, the700 MEO/LEO double-layer network mode is adopted. Among satellite orbital is generally km and 1500 km. The constellation satellites serving the MEO/LEO layer exist in network form, and thein SIN, MEO/LEO constellation network mode is adopted. Among them, them, the MEO satellites arethe mainly asdouble-layer routing exchange stars and access stars. The satellites are the network form,in and the SIN, the used MEO/LEO double-layer constellation network mode isLEO adopted. Among thethem, MEOthe satellites are mainly used as routing exchange stars and access stars. The LEO satellites are mainly mainly used as access stars, and they can access the application stars and ground stations. The composition MEO satellites are mainly used as routing exchange stars and access stars. The LEO satellites are structure of stars, the MEO/LEO layer satellite Figure 2. and used as access and stars, they can thesystem application starsinand ground stations. composition structure of mainly used as access andaccess they can access is theshown application stars groundThe stations. The composition
thestructure MEO/LEO layer satellite layer system is shown in Figure 2. in Figure 2. of the MEO/LEO satellite system is shown
LEO-2
LEO-1
MEO-1
LEO-1
MEO-1
MEO/LEO Layer MEO/LEO
LEO-2 LEO-4 MEO-3 LEO-3
LEO-4
Layer
MEO-2 MEO-3
LEO-3
MEO-2
Figure 2. Composition structure of the nonsynchronous medium earth orbit/nonsynchronous low earth orbit (MEO/LEO) layer satellite system. Figure Composition structure the nonsynchronous medium medium earth low Figure 2. 2. Composition structure ofofthe nonsynchronous earth orbit/nonsynchronous orbit/nonsynchronous low earth orbit (MEO/LEO) layer satellite system. earth orbit (MEO/LEO) layer satellite system.
Definition 4. (Near Space Layer Information System). The backbone networks of SIN are composed of satellite systems. However, satellite systems cannotSystem). achieve The all-weather, Therefore, Definition 4. (Nearthe Space Layer Information backbonelarge-depth, networks of and SIN full-coverage. are composed of satellite it is necessary to rely onsatellite the Nearsystems Space layer aircrafts, UAVs and HABs, to full-coverage. achieve the construction Definition 4. (Near Space Layer Information System). The backbone networks ofand SIN are composed of satellite systems. However, the cannot achieveincluding all-weather, large-depth, Therefore, of the Near Space layer information system. The Near Space layer is convenient for its condition, so theit is systems. However, the satellite systems cannot achieve all-weather, large-depth, and full-coverage. Therefore, it is necessary to rely on the Near Space layer aircrafts, including UAVs and HABs, to achieve the construction construction of Near Space layer information system is more flexible and more formal. The composition of the Near layer The Near Space layer convenient for its so the necessary to relySpace on the Nearinformation Space layersystem. aircrafts, including UAVs andisHABs, to achieve thecondition, construction of the structure of the system is shown in flexible Figure 3.and more formal. The composition construction of Near NearSpace Spacelayer layerinformation information system is more structure of the Near Space layer information system is shown in Figure 3.
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Near Space layer information system. The Near Space layer is convenient for its condition, so the construction of Near Space layer information system is more flexible and more formal. The composition structure of the Near Space layer 2018, information system is shown in Figure 3. Electronics 7, x FOR PEER REVIEW 4 of 25 Electronics 2018, 7, x FOR PEER REVIEW
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Blon-2 UA-3
UA-4
Blon-1 Blon-2
UA-5 UA-3
UA-4
Near Space Layer Near Space Layer
Blon-1 UA-5
Blon-3
UA-2 Blon-3 UA-1
Blon-4
Blon-5
UA-2 UA-1Unmanned
Fleet
Unmanned Fleet
Blon-4 balloon
SwarmBlon-5
balloon Swarm
Figure3.3.Composition Compositionstructure structure of the Near Figure Near Space Spacelayer layerinformation informationsystem. system. Figure 3. Composition structure of the Near Space layer information system.
Definition 5. (Ground Layer Terminals). In accordance with the original intention of the construction and (Ground Layer Terminals). Inspace accordance with the original intention of the construction Definition 5. of development SIN, it is mainly based on the platforms to achieve information acquisition and processingand Definition 5. (Ground Layer Terminals). In accordance with the original intention of the construction and as well as the task of assurance. the main tasks of information the ground terminals areand to maintain development of SIN, it information is mainly based on the Therefore, space platforms to achieve acquisition processing development of SIN, it is mainly based on the space platforms to achieve information acquisition and processing space We believe that the Ground the layermain of SIN is mainly composed of the following types as and wellmanage as the task of entities. information assurance. Therefore, tasks of the ground terminals are to maintain as well as the task of information assurance. Therefore, the main tasks of the ground terminals are to maintain of terminals: fixed-based stations, hand-held mobile-based stations, vehicle-based stations, and carrier-based andand manage space entities. layer of of SIN SINisismainly mainlycomposed composedofofthethe following types manage space entities.We Webelieve believethat that the the Ground Ground layer following types stations. Thefixed-based composition structure of the Ground layer terminals is shown in Figurestations, 4. of terminals: stations, hand-held mobile-based stations, vehicle-based and carrier-based of terminals: fixed-based stations, hand-held mobile-based stations, vehicle-based stations, and carrier-based stations. The composition shownininFigure Figure4.4. stations. The compositionstructure structureofofthe theGround Ground layer layer terminals terminals isis shown
Network Vehicle Station-2 Carrier Station-1
Carrier Station-1
Network
Network
Vehicle Station-2 Fixed Station-3
Network
Mobile Station-4
Ground Layer Ground Layer
Mobile Station-4
Fixed Station-3
Figure 4. Composition structure of Ground layer terminals. Figure4.4.Composition Composition structure of layer terminals. Figure of Ground Ground layer terminals.The basic design ideas Based on Definitions 1–5, we can design the top-level of SIN architecture. are building space-based backbone networks, including GEO and MEO/LEO layer satellite systems Based on Definitions 1–5, we can design the top-level of SIN architecture. The basic design ideas to solve global coverage issues, building a near-space backbone network including the Near Space areBased building space-based 1–5, backbone networks, including GEO andarchitecture. MEO/LEO layer systems on Definitions we can design the top-level of SIN The satellite basic design ideas layer information system to solve regional strengthening issues, and building Ground layer terminals to solve global coverage issues, building a near-space backbone network including the Near Space are building space-based backbone networks, including GEO and MEO/LEO layer satellite systems to to achieve command and control. Therefore, the SIN has a more obvious four-layer structure. layer information system to solve regional strengthening issues, and building Ground layer terminals solve global coverage issues, building a near-space backbone network including the Near Space layer to achieve command and control. Therefore, the SIN issues, has a more obvious four-layer structure. information system to solve regional strengthening and building Ground layer terminals to 2.2. Dynamic Visualization and Visual Analysis
achieve command and control. Therefore, the SIN has a more obvious four-layer structure.
NetworkVisualization visualizationand is aVisual branchAnalysis of information visualization that can be traced back to static graph 2.2. Dynamic visualization [7]. With gradual research, people found that topology evolution has become a major feature 2.2. Dynamic Visualization and Analysis Network visualization is Visual a branch of information visualization that can be traced back to static graph of networks. Therefore, static network visualization was unable to meet the real needs. Since then, scholars visualization [7]. With gradual found that topology evolution has a major Network visualization is aresearch, branchofpeople of information thatvisualization. canbecome be traced backfeature to static have gradually introduced the concept time and startedvisualization to study dynamic of networks. Therefore, static network visualization was unable to meet the real needs. Since then, scholars graph visualization [7]. With[8]gradual research, people foundItthat topology evolution become Dynamic visualization is a relatively young cross-field. is mainly used to research has the visual have gradually introduced the concept of time andnetwork started tovisualization study dynamicwas visualization. a major feature of networks. Therefore, static unable to meet the real view change laws due to the nodes and edge changes of the network over time. Dynamic Dynamic visualization [8] is a relatively young cross-field. It is mainly used to research the visual needs. Since then, scholars introduced the concept of time and started study visualization can make full have use ofgradually the human visual perception system to display dynamictodata view change laws due to the nodes and edge changes of the network over time. Dynamic dynamic visualization. graphically. On the one hand, it can help users to understand the internal structure of network, and visualization can make full use of the human visual perception system to display dynamic data a relatively young cross-field. is mainly used to researchupdated, the visual onDynamic the other visualization hand, it helps[8] to is uncover potential value, because It dynamic data is constantly graphically. On the one hand, it can help users to understand the internal structure of network, and andchange the impacts of the newly generated data on theoforiginal visualization areDynamic uncontrollable and view laws due to the nodes and edge changes the network over time. visualization on the other hand, it helps to uncover potential value, because dynamic data is constantly updated, poses a challenge to the to network dynamic visualization. Combined canunpredictable make full use[9]. ofTherefore, the humanthis visual perception system display dynamic data graphically. On the and the impacts of the newly generated data on the original visualization are uncontrollable and with the visual perception characteristics of the visual view, the design of dynamic visualization unpredictable [9]. Therefore, this poses a challenge to the network dynamic visualization. Combined should aim to ensure continuity and consistency between frames. with the visual perception characteristics of the visual view, the design of dynamic visualization People take visual analysis as the third paradigm after visualization in scientific computing should aim to ensure continuity and consistency between frames. (VISC) and information visualization, and it involves the inheritance and development of People take visual analysis as the third paradigm after visualization in scientific computing (VISC) and information visualization, and it involves the inheritance and development of
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one hand, it can help users to understand the internal structure of network, and on the other hand, it helps to uncover potential value, because dynamic data is constantly updated, and the impacts of the newly generated data on the original visualization are uncontrollable and unpredictable [9]. Therefore, this poses a challenge to the network dynamic visualization. Combined with the visual perception characteristics of the visual view, the design of dynamic visualization should aim to ensure continuity and consistency between frames. People take visual analysis as the third paradigm after visualization in scientific computing (VISC) and information visualization, and it involves the inheritance and development of visualization technology. VISC and information visualization are more inclined towards the previous view, and the visual analysis is more inclined towards post-analysis based on the visual view [10]. Visualization technologies have covered many aspects of people’s daily lives and work. With the widespread popularization of the Internet and mobile terminals, people can not only enjoy the technology dividends, but also realize that “one picture speaks one thousand words”, based on the visualization technologies. After decades of development, visualization has gradually developed into a valid area of data analysis. In addition, it has gradually developed from VISC, information visualization to big data visualization, dynamic visualization, and visual analysis as well as other directions and branches. Similar to other visualization technologies, there are some basic functional and performance requirements for dynamic visualization and visual analysis techniques. On the one hand, it is necessary to meet the basic aesthetic criteria throughout the visualization process [11]. On the other hand, the user’s mental map must always be maintained [12]. Meeting the above functional and performance requirements are the criteria for evaluating the effectiveness of the visualization. The literature presents three aspects to realize network dynamic visualization: network layout, network attribute visualization, and user interaction [4,8]. After the development over several years, scholars have also made many contributions concerning the three aspects presented above. A list of the common methods for the realization of dynamic visualization and visual analysis is shown in Table 1. Table 1. A list of the mainstream methods of dynamic visualization. Network Layout
Network Visualization
Network Interaction
Force-Directed Algorithm Improvement 1 Improvement 2 ...
Animation Timeline Fusion of above ...
Fisheye view Focus and context Multi-view association ...
As shown in Table 1, the network layout methods mainly include the Force-Directed Algorithm (FDA) layout and its improvements. The methods of network attribute visualization mainly include the animation method and the timeline method. The interactive methods mainly include the fisheye view method, the focus and context method, and the multi-view association coordination method. In this paper, we refer to and improve the methods described above to implement the SINDVis. Therefore, the specific contents of the above methods are not discussed in this section too much. In addition, development of dynamic visualization at home and abroad has been carried in prophase work [13], and this section does not elaborate on them further. 2.3. User Feature Analysis As mentioned in Section 1, the purpose of designing SINDVis is to assist multi-class users to achieve effective understanding, construction, development, maintenance, and management of SIN. Therefore, users are the core factor of the SINDVis design, and users’ requirements determine the SINDVis functions. That is to say, the various functions of SINDVis are designed to meet the multiple needs of multi-class users. Therefore, in order to put the idea of user-centered into practice and to provide guidance for the design and description of SINDVis functions in Section 3.2, this section carries out a user feature analysis of SINDVis.
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One of the main indicators for verifying visualization is satisfaction degree of the user’s visual experience. The primary indicator and original intention of the SINDVis system was to meet the needs of multi-class users. Therefore, we analyzed the characteristics of the existing users and potential users of the SIN to provide a reference for the development of the system function module. According to the needs of the similarities and differences of SINDVis, the main users were divided into three categories as follows:
•
•
•
USE-1: (Understanding Class Users). The first-class users are new to SIN, and they do not have much relevant background knowledge of SIN. Meanwhile, they need to have preliminary understanding of the composition and structure of SIN with the SINDVis. USE-2: (Construction and Development Class Users). The second-class users come from the demonstration and construction departments of SIN, and they have a certain understanding of SIN. However, they need to optimize and improve SIN. Therefore, they not only need to grasp the architecture of SIN in real-time, but also need to understand the evolvement laws and development situation of SIN with the SINDVis. USE-3: (Maintenance and Management Class Users). The third class users come from the maintenance and management departments of SIN, and they need to grasp the structure and change laws of SIN in real time. Meanwhile, they should grasp the position and relationship of key nodes and core links of SIN in the topology domain and effectively avoid the damage and interference of SIN. In addition, they can effectively maintain the normal operation of the SIN with the SINDVis.
In short, according to the different needs of users, we divided the SINDVis users into the three categories presented above. To show how different users focus on SINDVis views, we present a tabular representation of how much the user needs to use the SINDVis views. We use F to express the users’ demands for SINDVis, and a greater number of F indicates a greater need for views. The requirements of the users for the views are shown in Table 2. The contents of entity view, named GeoView, and topology view, named TopolView, are discussed in Section 3.2. Table 2. Degree of requirement of multi-class users. User Class
GeoView
TopolView
USE-1 USE-2 USE-3
FFF FF FF
F FFF FFF
3. Theory and Methods The purpose of this section is to introduce the related theory and methods of SINDVis. As we know that framework is a guidance for system design and implementation, we constructed the architecture of SINDVis first. Based on this, we illustrate the functions of GeoView in the entity domain and TopolView in the topology domain, respectively. The GeoView and TopolView play key roles in SINDVis, and the implementation principles of them are different, so we separately explain theory and methods of the GeoView and TopolView. In addition, we focus on the implementation methods of the TopolView in the topology domain, including an improved FDA (Force-Directed Algorithm) layout, FAT (Fusion of Animation and Timeline) visualization and P&Z (Panning and Zooming) interaction. 3.1. SINDVis Architecture The main purpose of visualization technologies is to satisfy users’ visual experience, and to realize the requirements of data analysis based on visual views. Network dynamic visualization is no exception. Therefore, we think that the SINDVis framework should include dynamic data input, visual view generation, visual view output, and users. Based on this, we designed the SINDVis framework as shown in Figure 5.
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Visual Method Set
View Set
Entity domain
Entity Data
Visualization
Interaction GeoView
Interaction Control
Mapping
Topology domain
Layout 1 Network data
Visualization Interaction 1 1
Interaction Control TopolView
Layout 2 Visualization 2
Interaction 2
Output
Input
Feedback
Figure architecture. Figure5.5.SINDVis SINDVis architecture.
As shown in Figure 5, the SINDVis wasconstructed constructed from a dataset (input module), As shown in Figure 5, the SINDVisframework framework was from a dataset (input module), a visual method set (core-processing module), a view set (output module), and a user a visual method set (core-processing module), a view set (output module), and a user body. Tobody. To demonstrate architecture more clearly, analyzed its composition moreasdetail, demonstratethe the SINDVis SINDVis architecture more clearly, we we analyzed its composition in moreindetail, shown below. as shown below.
•
•
•
Dataset: The dataset is an input module for SINDVis, consisting of an entity dataset and a
Dataset: The dataset is an input module for SINDVis, consisting of an entity dataset and a network network dataset, and the network data in topology domain is mapped from the entity data in dataset, and the network data in topology domain is mapped the entity in the entity the entity domain. The entity dataset consists of space data, suchfrom as satellite orbitaldata parameters, domain. Theoperating entity dataset of spacecoverage, data, such as transfer satellitebetween orbital parameters, satellite satelliteconsists cycles, satellite data satellites, etc. satellite By operating satellite data transfer between satellites, By mapping mapping space cycles, entities satellite to nodes coverage, and by mapping relationships between entities etc. as edges, we thetonetwork of therelationships above providebetween input to the SINDVis. spaceformed entities nodes dataset. and by Both mapping entities as edges, we formed the Visual method set: The visual method set is a core-processing module of SINDVis and it includes network dataset. Both of the above provide input to the SINDVis. the entity domain methods and topology domain methods. For the entity domain, we refer toincludes the Visual method set: The visual method set is a core-processing module of SINDVis and it visual views of STK and SaVi and realize the dynamic display of the structure and running state the entity domain methods and topology domain methods. For the entity domain, we refer to of the SIN in the entity domain. For the topology domain, we realize the dynamic display of the visual views of STK and SaVi and realize the dynamic display of the structure and running evolution laws of the SIN topology structure. The visual method set is a large collection of statemethods, of the SIN the entityofdomain. the topology domain, we realize the dynamic andinthe essence the visualFor method set is a black box. The implementation methodsdisplay of of evolution of the SIN include topology structure.and Theinteraction visual method setThe is aimplementation large collection of the entitylaws domain mainly visualization methods. methods, andofthe of domain the visual method set layout, is a black box. The and implementation methods of methods theessence topology mainly include visualization interaction methods. Because of the different and different objects the entity domain and The topology domain, the entity domain mainlyprinciples include visualization and of interaction methods. implementation the implementation methods of each are also different. methods of the topology domain mainly include layout, visualization and interaction methods. View view set is the output the SINDVis, the entity view, Because ofset: theThe different principles and module differentofobjects of the including entity domain and domain topology domain, named GeoView, and the topology domain view, named TopolView. As we know, the visual the implementation methods of each are also different. view is a direct embodiment of the implementation of visualization technologies, and it is also a View set: The view set is the output module of the SINDVis, including the entity domain view, medium for showing information and implementing user interactions. Meanwhile, we think of named andset theastopology domain named TopolView. Aswe we know, thethe visual the GeoView, visual method processing, and theview, view set as results. Therefore, constructed viewvisual is a direct embodiment of the implementation of visualization technologies, and it is method set and the view set separately. In SINDVis, the GeoView and TopolView appearalso a medium for showing andOf implementing user interactions. weand think of on different pages information at the same time. course, the specific display formsMeanwhile, of the GeoView the visual method set as and the view set as results. Therefore, we set constructed TopolView depend onprocessing, the specific visual methods selected. Meanwhile, the view can feed the themethod user’s new requirements intoseparately. the input In module and the core-processing module, thus visual set and the view set SINDVis, the GeoView and TopolView appear generating output modules that meet users’ new requirements. on different pages at the same time. Of course, the specific display forms of the GeoView and TopolView depend on the specific visual methods selected. Meanwhile, the view set can feed the user’s new requirements into the input module and the core-processing module, thus generating output modules that meet users’ new requirements.
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Users: Users are the center of the SINDVis, and users’ requirements are the basis reference for SINDVis function settings. Visual interaction is built between the view set and users. Meanwhile, the users enable real-time interaction with the view, and the users can control the views in real-time. Because the SINDVis is a dynamic visualization system, the main interaction is the time control of users. In addition, due to the limitations of page size, users can zoom in, zoom out, or pan the views according to their own interests. It is also one of the main visual interactive functions of the SINDVis.
In fact, the data is the input, the views are the output, and the visual methods are a black box. In this paper, we introduce visualization technologies into SIN and aim to design and realize the SINDVis. Therefore, to highlight the key methods and theory of SINDVis, we replace the black box with the visual method set in Figure 5. Meanwhile, we think that the visual method set in the SINDVis architecture is necessary. The datasets involved in the architecture are more focused on data collection and storage. Therefore, we rely on the SIN database for the storage of space data. The SIN database is a distributed file system (Hadoop distributed file system, HDFS) that is used for the development of a column-oriented distribution storage system. Project groups built it on the Hadoop platform. The specific contents [14] of the SIN database are not explained further in this article. The content of the visual method set and the interactive control technologies involved in the SINDVis framework architecture are explained in Section 4. 3.2. SINDVis Description of Functions The views reflect the functions of SINDVis. In Section 2.3, we presented an analysis of the different needs of different users for visual views, and in Table 2, we also mentioned GeoView and TopolView. GeoView is the short name for the entity domain view, and TopolView is the short name for the topology domain view. GeoView is a direct embodiment of the entity organization relationship of SIN, and TopolView is used to show dynamic evolution processes and grasp the topology evolution laws of SIN after the entity data has been mapped to the network data. In addition, they complement each other. Detailed information is shown below. 3.2.1. Descriptions of GeoView Functions Based on the inspiration of the STK [15], and in order to complement the TopolView, we developed a web-oriented visual view, GeoView. This view is not only able to implement the features that STK contains, but also partially expands. The specific functions are as follows.
•
•
• •
Function 1: GeoView can realistically simulate and demonstrate the composition and operational status of SIN, and it can achieve a stereoscopic display (3D) and planar display (2D). Meanwhile, the view also can display the relevant geospatial environment. Function 2: GeoView can show the specific network structure and connection relations of the GEO layer satellite system and the MEO/LEO layer satellite system. It can show the orbit and coverage of the satellite systems. In addition, GeoView can display the group style, running mode, and coverage range of unmanned aircrafts (UAs) and the hot air balloons (HABs) in the Near Space layer information system. Meanwhile, it can also show the specific locations of Ground layer terminals and their connections with other information systems. Function 3: GeoView can determine the parameters of visual elements by setting a hot zone, and demonstrating the dynamic transmission of data information among different links. Function 4: GeoView can enable freely switching of 3D, 2.5D, and 2D information, and it can also switch multiple map backgrounds and operating environments. Meanwhile, it can realize the real-time synchronization of data information. Users can zoom in and zoom out of the views freely based on individual needs. This means that the overall view information can be displayed as well as the detailed view information, and the whole process will not cause the distortion of the view.
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According to the users’ needs, we initially set the functions of GeoView in the entity domain presented above. Wherein, the functions may have repetition. In order to express different goals, and we carried out the elaboration separately. Of course, there are many more GeoView functions, and they can be developed and expanded according to the needs of users. 3.2.2. Descriptions of TopolView Functions GeoView is responsible for the visual presentation and analysis of the entity domain. However, the expansion of SIN, and the increase in functions require an analysis of its topology structure and topology evolution. Therefore, it is necessary to make use of the ideas of the complex network. The space entities of SIN were mapped into network nodes, and relations between entities were abstracted as network links to analyze the network performance of SIN. Based on this, we designed TopolView in the topology domain. The aim of building the TopolView is to determine the network performance and network characteristics of SIN based on visual means, such as the importance of nodes, the key links, and the dynamic topology evolution laws. Therefore, we think that the TopolView should have the following functions.
•
•
•
•
Function 1: TopolView should show the complete topology structure of the SIN and realize the network expansion display of the four-layer structure. It should show the tight coupling relationships within the layers and the loosely coupled connections between the layers. Function 2: TopolView should show the network features, such as the key nodes and important links of SIN, on the same page. The key nodes and important links are the core of the whole network, and they are the cornerstone of normal operation of SIN. Therefore, it is important for all people involved in the construction, development, maintenance, and management of SIN to master this information. Function 3: TopolView should show the dynamic evolution laws of SIN. Under the guidance of topology evolution rules, including node increment, node deletion, link increment, and link deletion, it is possible to display the vibrations and changes in the network topology. Which are caused by the changes in nodes and edges in SIN. Within a certain time by the sliding of the time slice, it will keep a new stable state. Function 4: TopolView should assist in the optimization of SIN through the cleanup of network topology-independent nodes and unrelated links, including the deletion of unimportant nodes and unrelated links. It should also optimize the SIN structure scale and reduce duplication in construction.
TopolView is the main research part of SINDVis. The simulation and display of the TopolView of SINDVis is an effective method and means to construct and manage the SIN for USE-2 and USE-3. Therefore, the dependency on TopolView is also strong. This section describes the four functions above in relation to the different requirements. Similar to the GeoView, the topology domain view has many more functions than those described above, and they can be developed and expanded according to the needs of users. As discussed in the introduction, with the construction and development of SIN, its scale will increase continuously, and its structure will become more and more complex. Meanwhile, real-time changes in SIN topology will bring more uncertainties. All of them bring many challenges to the maintenance and management of SIN. In previous work, we established a weighted, dynamic evolution model based on local-world SIN [16]. The model combines the local-world phenomenon and edge-right features of SIN. However, the model only validates some characteristics of SIN from the network theory perspective. As we know, 70% of information acquired by people is done with the eyes. Meanwhile, visualization technologies not only formalize display views, but also can excavate hidden information behind views. Therefore, we think that we can also explore the dynamic evolution laws of SIN based on the dynamic visual view. Therefore, we initiated the idea of designing TopolView in the topology domain. On the one hand, TopolView can display the dynamic evolution processing of SIN. On the
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other hand, it can be used to analyze the changing relationships between the key nodes and core summarized to provide some guidance for the construction, development, management, and links of SIN. Based on this, the dynamic evolution laws of SIN can be summarized to provide some maintenance of SIN. This also involves the specific implementation of visualization technologies to guidance for the construction, development, management, and maintenance of SIN. This also involves support the analysis of the network. the specific implementation of visualization technologies to support the analysis of the network. 3.2.3. Description of the Fusion Usage of Views 3.2.3. Description of the Fusion Usage of Views As mentioned above, for multi-class users, the GeoView and TopolView complement each other. As mentioned above, for multi-class users, the GeoView and TopolView complement each other. The principles of specific supplemental use are summarized as follows. The principles of specific supplemental use are summarized as follows. Firstly, The GeoView is the entity domain view, and when the scale of SIN is small, it is simple Firstly, The GeoView is the entity domain view, and when the scale of SIN is small, it is simple to to show its composition structure and operation laws. However, the scale of SIN is constantly show its composition structure and operation laws. However, the scale of SIN is constantly increasing, increasing, and the structure of SIN is becoming more complex. When the scale of SIN develops to a and the structure of SIN is becoming more complex. When the scale of SIN develops to a certain certain degree, the GeoView will only be able to display its constituent structure but will not analyze degree, the GeoView will only be able to display its constituent structure but will not analyze its its operation laws. operation laws. Secondly, The TopolView is the topology domain view, and it is an abstract form with the space Secondly, The TopolView is the topology domain view, and it is an abstract form with the space entities of SIN mapped into network nodes, and relations between entities are abstracted as the entities of SIN mapped into network nodes, and relations between entities are abstracted as the network network links of SIN. The TopolView demonstrates the dynamic evolution process of SIN from a links of SIN. The TopolView demonstrates the dynamic evolution process of SIN from a network network perspective. Meanwhile, the dynamic evolution process is demonstrated without perspective. Meanwhile, the dynamic evolution process is demonstrated without considering the considering the scale of SIN. In addition, TopolView also can support the visual analysis of the scale of SIN. In addition, TopolView also can support the visual analysis of the changing relationships changing relationships between the key nodes and core links of SIN. between the key nodes and core links of SIN. To sum up, TopolView can be used to complement an insufficient GeoView with limited To sum up, TopolView can be used to complement an insufficient GeoView with limited presentation. The GeoView can complement the abstract features of TopolView by providing an presentation. The GeoView can complement the abstract features of TopolView by providing an intuitive display. Therefore, only by using these two complementary views in combination can the intuitive display. Therefore, only by using these two complementary views in combination can the SINDVis can play its role to the fullest. SINDVis can play its role to the fullest. 3.3. GeoView GeoView Methods Methods 3.3. As aa scripting scripting language, language, Cesium Cesium was was created created for for aa cross-platform cross-platform virtual virtual globe globe display display by by AGI AGI As (Analytical Graphics, Inc., Exton, PA, USA) in 2011. Initially, people primarily used Cesium for (Analytical Graphics, Inc., Exton, PA, USA) in 2011. Initially, people primarily used Cesium for dynamic data visualization in space and defense industries. Later, Cesium gradually developed into dynamic data visualization in space and defense industries. Later, Cesium gradually developed a 3Da 3D mapmap andand is is used in inmulti-fields, agriculture, into used multi-fields,including includinggeographical geographical space, space, oil, oil, gas, gas, agriculture, entertainment, and sports [17]. According to data from Cesium’s homepage, over 140 cases have been been entertainment, and sports [17]. According to data from Cesium’s homepage, over 140 cases have successfully implemented based on Cesium.js. They cover space, defense, smart cities, geo-space, successfully implemented based on Cesium.js. They cover space, defense, smart cities, geo-space, sports, entertainment, entertainment, and and so so on. on. Combined GeoView and and the the successful successful sports, Combined with with the the functions functions of of GeoView application of Cesium in other fields, the implementation of GeoView based on Cesium.js is application of Cesium in other fields, the implementation of GeoView based on Cesium.js is feasible. feasible. Therefore, we implemented the GeoView based on Cesium.js in this study. The specific technologies Therefore, we implemented the GeoView based on Cesium.js in this study. The specific technologies are not not discussed discussed much much in in this this section. section. However, However, because because the the GeoView GeoView is is dynamic, dynamic, the the Cesium Cesium time time are panel was used to achieve time control, as shown in Figure 6. panel was used to achieve time control, as shown in Figure 6.
Figure 6. GeoView time control module. Figure 6. GeoView time control module.
As shown in Figure 6, the left part of Cesium time panel is the control panel, including the As shown in Figure 6, the left part of Cesium time panel is the control panel, including the clockwise/counterclockwise, play/pause, and fast forward/slow operation buttons. The right side is clockwise/counterclockwise, play/pause, and fast forward/slow operation buttons. The right side is the specific timeline display, where the default time interval was set as 24 h in this study. the specific timeline display, where the default time interval was set as 24 h in this study. 3.4. TopolView Methods 3.4. TopolView Methods As mentioned in Sections 2.2 and 3.1, the realization of network dynamic visualization mainly As of mentioned in Sections 2.2layout, and 3.1, the realization of network dynamic mainly consists three aspects: network network attribute visualization, and uservisualization interaction. Layout consists of three aspects: network layout, network attribute visualization, and user interaction. Layout determines the network structure and is the most important element. Therefore, in accordance
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determines the network structure and is the most important element. Therefore, in accordance with the sequence above, we analyzed the theory and methods of realizing the TopolView. Therefore, we proposed an improved FDA layout method, discussed the FAT visualization method, and analyzed the P&Z interactive method. The specific implementation of the methods mentioned above is shown in Section 4.2. 3.4.1. FDA Layout As the first step of visualization, the layout determines the basic structure of the network and is the premise and basis for follow-up work. Typically, the visualization layout is divided into nine kinds, including the layer layout, circular layout, time layout, relative space layout, cluster layout, map layout, manual layout, random layout, and Force-Directed Algorithm (FDA) layout [18]. According to the statistics of the layout algorithms published in a paper on the IEEE Visualization and Computer Graphics (TVCG) of network visualization, 72.12% of the articles used the FDA layout based on the elastic model. The main idea of the FDA layout is that all nodes are randomly arranged in two-dimensional space at the beginning, and the node positions are iteratively optimized by simulating the gravitational and repulsive forces in the physical model to improve the layout effect gradually. The advantages of the FDA layout are mainly embodied in two aspects, one is easy to implement in operation, and the other is easy to understand and explain in cognition. The FDA mainly includes a basic algorithm and its improvement, such as the Kamada–Kawai (KK) algorithm, the Davidson–Harel (DH) algorithm, the Fruchterman–Reingold (FR) algorithm or the multi-scale algorithm [18]. For the time-varying network visualization layout, the article [19] improves the FR algorithm and considers the connection and disconnection of the edge in the concrete operation. For the SIN, different space entities play different roles in the entity domain, and the different nodes have different degrees of importance in the mapping of the topology domain. However, the importance of nodes affects the connections of edges. An algorithm that highlights the nodes’ levels of importance can accurately reflect the real performance of SIN. In the preliminary study, we established the topology evolution rules for the topology evolution of SIN, and they include not only the connection and disconnection of edges, but also the increment and deletion of nodes. Therefore, under the guidance of the topology evolution rules and the FR algorithm, we introduced clustering coefficients to calculate the importance of nodes and took node addition, node deletion, link addition, and link deletion into account to realize the effective layout of the dynamic visualization of SIN. The basic principle of the FR algorithm is the simulation of the motion of atoms and celestial bodies by analyzing the attraction and repulsion between the vertices and edges of the network. This method considers that there is attraction between the vertices and edges and that the vertices are mutually exclusive [19]. In the concrete implementation, spatial coordinate changes between the nodes are calculated by simulating the forces of the atom balls, and then the temperature variable and the cooling function are introduced, and the positions of all vertices are calculated by multiple iterations using the simulated annealing algorithm. The three steps taken to complete each iteration are as follows:
• • •
Step 1: Calculation of the repulsion forces between vertices and determination of the displacement vector (disp1) according to the repulsion forces. Step 2: Calculation of the attraction and final displacement vector (disp2) according to the gravitational and displacement vector (disp1). Step 3: Use of the cooling function to limit the range of motion of the vertex.
The FR algorithm optimizes the iterative calculation process by means of space grid partitioning. It reduces the computational complexity by considering the repulsion effect between the network nodes and the internal nodes of the adjacent network. For the problem of network dynamic visualization, we modified the FDA layout method based on the FR algorithm and achieved a dynamic layout by considering the phenomenon of node increment, node deletion, edge increment, and edge deletion.
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For the phenomenon of the increment and deletion of edges in dynamic problems, we designed fade-in and fade-out functions and made the network edges increase or disappear in an orderly manner to allow the layout to be smoothly and dynamically changed. This follows the same principle as the FR algorithm, and assumes that the edges only affect attraction and do not affect the repulsion. M represents the number of iterations, and l represents an iterative index. The expressions of the fade-in and fade-out functions are f in (d) =
d2 ( l − 1) ,1 ≤ l ≤ M k ( M − 1)
(1)
f out (d) =
d2 ( M − l ) ,1 ≤ l ≤ M k ( M − 1)
(2)
where, for the fade-in function f in (d), the value of attraction is 0 when there is no connection, and the value of attraction is f a (d) in the last iteration, and for the fade-out function f out (d), the value of attraction is f a (d) at the initial moment, and the value of attraction is 0 in the last iteration. For the phenomenon of the increment and deletion of nodes in dynamic problems, because attraction and repulsion exist in each pair of nodes, the importance of nodes was considered in the improved algorithm. The attraction and repulsion between nodes depend not only on their distance, but also on the importance of nodes. When the new node vi joins, there is a connection with its neighboring node v j , and the attraction and repellant between the two nodes is affected by the node’s importance. Therefore, we introduced the clustering coefficients of complex networks [20] to calculate the importance of nodes, and the clustering coefficient was calculated as follows: Ci =
2Ei k i ( k i − 1)
(3)
where, k i indicates that there are k i edges connected to node i, and Ei represents the number of edges between i and k i . Meanwhile, when k i = 0 or k i = 1, then Ci = 0, and in order to avoid this situation, we improved Ci by adding the number 1. The expression is NCi =
2Ei + 1. k i ( k i − 1)
I Mij denotes the importance of nodes vi and v j , and the calculation formula is q I Mij = NCi + NCj .
(4)
(5)
After the introduction of I Mij , the attraction and repulsion between the nodes will change with the clustering coefficients, which is well in line with the real network situation. The greater the I Mij is between nodes vi and v j , the greater the attraction between them is and the smaller the repulsion is, or vice versa. Therefore, the attraction between the nodes should be proportional to the I Mij , and the repellant should be inversely related to the I Mij . Therefore, to improve the Formula (1), there is ( f aim (d) = I Mij ·d2 /k (6) 1 f rim (d) = − I M ·k2 /d ij
where, f aim and f rim respectively represent attraction and repulsion, considering the nodes’ levels of importance. When node vi is deleted, the attraction and repulsion between the nodes connected to it disappear, which is relatively simple and has not been explored much. According to the dynamic evolution rule of SIN, we proposed an improved FDA layout method based on the FR algorithm. Similar to other improved methods of the FDA layout, we think that this improved FDA layout method also belongs to the FDA family. Therefore, we categorized this
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section as having an FDA layout. In the implementation algorithm of the improved FDA layout method, we separated the node and the edge, and this part did not have a specific display. This section, combined with the characteristics of the dynamic change of SIN, we have described the design of the improved FDA layout based on the FR algorithm and on the foundation for the SIN dynamic visualization. Next, we describe the visualization method. Electronics 2018, 7, x FOR PEER REVIEW
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3.4.2. FAT Visualization
3.4.2. FAT Visualization
Dynamic visualization plays a key role in network performance analysis, but due to the complexity Dynamic visualization plays a key role in network performance analysis, but due to the of complexity dynamic data, the evolution process visualization is difficult to determine. Overall, the realization of dynamic data, the evolution process visualization is difficult to determine. Overall, the methods of dynamic visualization are generally divided into two categories including animation and realization methods of dynamic visualization are generally divided into two categories including timeline [13], and they have also become the current mainstream form. Figure 7 shows a detailed animation and timeline [13], and they have also become the current mainstream form. Figure 7 showslist of amethods visualization. detailedfor listimplementing of methods for dynamic implementing dynamic visualization.
Dynamic Visualization Animation-based Technology
Timeline-based Technology
+ ? Node-line-based Technology
Online-based Technology
+ Matrix-based Technology
+ Offline-based Technology
List-based Technology
Figure7. 7. List List of visualization visualization methods. Figure methods.
shownininFigure Figure7,7,the theanimation animation method method maps domain and AsAs shown maps time timeinformation informationtotothe thetime time domain and user analyzesthe the dynamic dynamic network mode by observing and analyzing the animation. This user analyzes networkfluctuation fluctuation mode by observing and analyzing the animation. method requires the the useruser to remember the differences between the network structure and time step, This method requires to remember the differences between the network structure and time and then analyze the fluctuation mode of the dynamic network. Therefore, the key to the method is step, and then analyze the fluctuation mode of the dynamic network. Therefore, the key to the method determining how mutation. Animation is determining how to to keep keep the the user’s user’smind mindmap mapatatthe thesame sametime timeasasthe thenetwork network mutation. Animation methods mainly include two aspects: online and offline [8]. The timeline method maps time to to thethe methods mainly include two aspects: online and offline [8]. The timeline method maps time space domain, and users need to observe several snapshots at the same time to determine the space domain, and users need to observe several snapshots at the same time to determine the difference difference by comparing the differences between each other. As the scope of the screen is limited, by comparing the differences between each other. As the scope of the screen is limited, when there when there are many time steps, it is difficult to display all of network information at the same time, are many time steps, it is difficult to display all of network information at the same time, and this is and this is the main difficulty of this method. The timeline consists mainly of node-links, adjacency the main difficulty of this method. The timeline consists mainly of node-links, adjacency matrices, matrices, and lists three methods. and lists three methods. As mentioned above, the development of visualization gradually highlights the applicationAs mentioned above, the development of visualization gradually highlights the application-driven driven characteristics. Only by fully considering the characteristics of SIN can the visualization be characteristics. fully considering the characteristics of SIN can the visualization be more more effective.Only The by local-world phenomenon edge-weight evolution of SIN is the key factor in effective. The local-world phenomenon edge-weight evolution of SIN is the key factor in studying studying the topological evolution of SIN [16], and the main objective of dynamic visualization is to theanalyze topological evolution evolution of SIN [16], andbythe main objective of dynamic to analyze its topological laws a formal means. Therefore, wevisualization also need toisfocus on the its topological evolution laws by a formal means. Therefore, we also need to focus on the analysis of the analysis of the above-mentioned characteristics. above-mentioned characteristics. Data transmission is different depending on the SIN transmission direction, so, we needed to consider the transmission directionality; this part is introduced in Section 4. The dynamic changes in SIN mainly include the addition and deletion of nodes, the addition and deletion of edges, and so on. Through analyzing the advantages and disadvantages of the above methods, combined with the characteristics of the topological evolution of SIN, we tried to achieve the dynamic evolution visualization of SIN by fusing the animation and the time line method named FAT. Figure 8 shows a schematic diagram of the evolution of the local-world and edge-weight of SIN.
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Data transmission is different depending on the SIN transmission direction, so, we needed to consider the transmission directionality; this part is introduced in Section 4. The dynamic changes in SIN mainly include the addition and deletion of nodes, the addition and deletion of edges, and so on. Through analyzing the advantages and disadvantages of the above methods, combined with the characteristics of the topological evolution of SIN, we tried to achieve the dynamic evolution visualization of SIN by fusing the animation and the time line method named FAT. Figure 8 shows a schematic of PEER the evolution Electronics diagram 2018, 7, x FOR REVIEW of the local-world and edge-weight of SIN. 14 of 25 Electronics 2018, 7, x FOR PEER REVIEW 6
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Figure The local-worldand andedge-weight edge-weight evolution evolution mechanism network Figure 8. 8. The local-world mechanismofofthe thespace spaceinformation information network Figure(a) The local-world and edge-weight evolution mechanism of information network (SIN): node increase mechanism; mechanism; (b) deletion mechanism; (c)the edge increase mechanism; (d) (SIN): (a) 8.node increase (b)node node deletion mechanism; (c)space edge increase mechanism; (SIN):deletion (a) node increase mechanism; (b) node deletion mechanism; (c) edgefrom increase mechanism; (d) (e)(e) edge-weight evolution mechanism (adopted Yu etYu al.et [16]). (d)edge edge deletionmechanism; mechanism; edge-weight evolution mechanism (adopted from al. [16]). edge deletion mechanism; (e) edge-weight evolution mechanism (adopted from Yu et al. [16]).
AsAs shown above, Figure 8a–d8a–d are the mechanisms for node node deletion, shown above, Figure are evolutionary the evolutionary mechanisms for increment, node increment, node As shown above, Figure 8a–d are8e the evolutionary mechanisms node edge increase, and edge deletion. Figure represents the mechanism offor thenode edge-weight evolution. deletion, edge increase, and edge deletion. Figure 8e represents the mechanism of increment, the edge-weight deletion, edge increase, and edge deletion. Figure 8e represents the mechanism of the edge-weight The future sequence of SIN is unknown, us toforcing rely onus online methods to methods determine animation evolution. The future sequence of SIN isforcing unknown, to rely on online toits determine evolution. Theform. future sequence of SIN is transition unknown,and forcing ustransitional to rely on online methodstotoprotect determine its animation The use of gradual other technologies form. The use of gradual transition and other transitional technologies to protect the user’s mindthe map its animation form. The of gradual transition and other technologies to protect the user’s does notuse allow violent shocks so achieves antransitional effective animation display. does notmind allowmap violent shocks so achieves an effective animation display. user’s mind map does not allow violent achieves an effective animation display. For the local-world phenomenon ofshocks SIN, it it so is necessary between thethe For the local-world phenomenon of SIN, is necessaryto tohighlight highlightthe thedifferences differences between For the local-world phenomenon of SIN, it is necessary to highlight the differences between the outside local-world and inside local-world, and there is a typical preferential connection mechanism outside local-world and inside local-world, and there is a typical preferential connection mechanism in outside local-world and inside local-world, and there is a typical preferential connection mechanism the local-world. Therefore, we need the constraint of double coding to highlight similarities theinlocal-world. Therefore, we need the constraint of double coding to highlight thethe similarities and in the local-world. Therefore, we needoutside the constraint of double coding to highlight thethe similarities and differences between the factors and inside the local-world. Based on relevant differences between the factors outsideoutside and inside the local-world. Based on the relevant principle and differences between the factors andnetwork inside the Based on the relevant of centroid constraint in the community [21],local-world. we produced a visual view of the of principle centroid constraint in the community network [21], we produced a visual view of the local-world principle of phenomenon centroid constraint theThe community network [21], a visual view of the local-world in the in SIN. typical characteristic of we the produced local-world is the preferential phenomenon in the SIN. The typical of the local-world is the preferential connection local-worldmechanism, phenomenon in the the SIN.characteristic Theconstraint typical characteristic of the local-world is themove preferential connection and centroid is used to make the network nodes closer mechanism, and the centroid constraint is used to make the network move closer to the centroid connection mechanism, the centroid used to make nodes the network move closer to the centroid of their and community and constraint to realize is the aggregation effect in thenodes geometric space. of their community and tocommunity realize the aggregation effect in the geometric space. Therefore, the above to the centroid of their and to realize the aggregation effect in the geometric space. Therefore, the above two aspects have the same effect on the display. The multi-centroid constraint two aspects have the same effect on the display. The multi-centroid constraint diagram is shown Therefore, the above two aspects have the same effect on the display. The multi-centroid constraint in diagram is shown in Figure 9. Figure 9. is shown in Figure 9. diagram
Figure9.9. Multi-centroid Multi-centroid constraint Figure constraintdiagram. diagram. Figure 9. Multi-centroid constraint diagram.
The centroid constraint is implemented based on FDA and the effect of clustering and clustering The centroid based on FDA and effect of clustering and constraint clustering is formed under constraint the action isofimplemented nodal centroid attraction [22].the Therefore, the centroid is formed under the action of nodal centroid attraction [22]. Therefore, the centroid constraint concretely implements the content same strain with FDA, which also provides the possibility for concretely implements the content same strain with FDA, which also provides the possibility practice in this paper. Considering the local-world has = { , … , } , and the location of for its practice in this paper. Considering the local-world has = { , … , } , and the location of its
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The centroid constraint is implemented based on FDA and the effect of clustering and clustering is formed under the action of nodal centroid attraction [22]. Therefore, the centroid constraint concretely implements the content same strain with FDA, which also provides the possibility for practice in this paper. Considering the local-world has Cr = {vi , . . . , vk }, and the location of its arbitrary node vt is Electronics 2018, 7, x FOR PEER REVIEW 15 of 25 ( xt , yt ), the position of the centroid vr inside the local-world Cr is vr = ( xr , yr ), and there is (
11 k xr = ∑ i=1 =k ∑ =1 x t . 1 k yr = k1 ∑i=1 yt. = ∑ =1
(7) (7)
Assuming that the constrained attraction of the node vt is f (vr ), and the direction of the current Assuming that the constrained attraction of the node is ( ), and the direction of the node points to the centroid, there is current node points to the centroid, there is f (vr ) = d × strengthℎ( (Cr ))
(8) (8)
where, is the distance from the node to the centroid of the local-world, and ℎ( ) where, d is the distance from the node vt to the centroid vt of the local-world, and strength(Cr ) is the is the attraction strength. Therefore, there is attraction strength. Therefore, there is (9) = | − |= q − = q( − ) − ( − ) . d = ||vt − vr || = dx2 − dy2 = ( xt − xr )2 − (yt − yr )2 . (9) Combining Equation (8), the constrained attraction of in the x-direction and y-direction, respectively, gives Combining Equation (8), the constrained attraction of vt in the x-direction and y-direction, respectively, gives × ℎ( ) ( ( ) = × ( )= (10) f (vr ) X = dx × f v = dx × strength ( ) (Cr ). r d (10) ( ) = dy × ( )= × ℎ( ) . f (vr )Y = d × f (vr ) = dy × strength(Cr ) Along wewe cancan obtain the constrained attraction of other of v of and Along the thesame samevein, vein, obtain the constrained attraction of nodes other nodes Crother and j local-world regions. Therefore, the resultant force of the after considering the constrained other local-world regions. Therefore, the resultant force of the vt after considering the constrained attraction is attraction is
f = = f ((vr )) + + fa + + f r ..
(11) (11)
For the phenomenon of the edge-weight evolution of SIN, we intended to construct the visual view by double curve. Because this part is double coding codingincluding includingthe thethickness thicknessand andcolor colorofofthe theconnection connection curve. Because this part easier, wewe dodo notnot discuss it in detail. is easier, discuss it in detail. In the visual view of GeoView, the time of the current scene is displayed and controlled by the “widget wewe also added a timeline in “widget Cesium Cesiumtimeline”. timeline”.In Inorder ordertotocorrespond correspondtotothe theview viewofofGeoView, GeoView, also added a timeline thethe visual view of TopolView for the user manipulate and track thetrack details the network in visual view of TopolView for thetouser to manipulate and theofdetails of theevolution network of interest of to interest the user to in the different moments periods. or Therefore, designedwe and added the evolution user in differentormoments periods.we Therefore, designed andtimeline added module in TopolView, shown in Figure 10. in Figure 10. the timeline module inas TopolView, as shown
A B 0
1
2
3
4
5
6
7
Figure Figure 10. 10. The The timeline timeline schematic schematic of of TopolView. TopolView.
As shown in Figure 10, the timeline module of TopolView consists mainly of two parts: A is the and B B is is the the time time bar which is used to control module module including including play/pause play/pause and fast forward/rewind, and display moment and time fragments. this section discussed the theory of FATof visualization includingincluding the specificthe theoretical To sum sumup, up, this section discussed the theory FAT visualization specific components and implementation methods. Since the implementation of FAT is based onisimproved theoretical components and implementation methods. Since the implementation of FAT based on FDA, the FAT visualization algorithm is no longerisspecific. improved FDA, the FAT visualization algorithm no longer specific. 3.4.3. P&Z Interaction Interaction technology is inseparable from the visual analysis, and all interaction technologies are only meaningful when combined with a visual interface. There are some representative technologies of interactive visual analysis of detailed information, and most of them are based on
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3.4.3. P&Z Interaction Interaction technology is inseparable from the visual analysis, and all interaction technologies are only meaningful when combined with a visual interface. There are some representative technologies of interactive visual analysis of detailed information, and most of them are based on Electronics 2018, 7, x FOR PEER REVIEW 16 of 25 deformation technology. As Table 1, the interactive techniques commonly used in theused field in of visualization As shown showninin Table 1, current the current interactive techniques commonly the field of 1categories: 2 focus 3 overview can be summed the following categories: fisheye views,
and② context, visualization canup beby summed up by the following ① fisheye views, focus and context, 4 5 and details,
panning and zooming,
multiple coordinated views, and so on [23]. We carried out ③ overview and details, ④ panning and zooming, ⑤ multiple coordinated views, and so on [23]. aWe detailed review of the above-mentioned methods in previous research work [4,13], and we do not carried out a detailed review of the above-mentioned methods in previous research work [4,13], elaborate much on it in this section. the canvas area used to drawarea the network dynamic and we do not elaborate much on itAdmittedly, in this section. Admittedly, the canvas used to draw the topology is limited, and the nodes and edges of the SIN topology have a certain scale. To clearly network dynamic topology is limited, and the nodes and edges of the SIN topology have a certain display the information the TopolView,inwe used the panning and zooming (P&Z) interactive scale. Toallclearly display allin the information the TopolView, we used the panning and zooming technology to realize the dynamic interactive function of the user. (P&Z) interactive technology to realize the dynamic interactive function of the user. P&Z onto a P&Z is is an an interactive interactive technology, technology,and andititsolves solvesthe theproblem problemofoffitting fittinglarge largeamounts amountsofofdata data onto smaller screen [24]. In In this study, we we borrowed the the P&ZP&Z interaction model proposed by Wijk and Nuij a smaller screen [24]. this study, borrowed interaction model proposed by Wijk and to implement the TopolView; the basic principles are shown in Figure 11. Nuij to implement the TopolView; the basic principles are shown in Figure 11.
w wm
s=sA
pan
s=sB
zoom out w0 w
zoom in
s=0
1
s=S u0
u1
u
Figure 11. Diagram Diagramofofthethe space panning zooming (P&Z) reduction, translation, 2D2D space of of panning andand zooming (P&Z) reduction, translation, and and amplification (adopted from Wijk et al. [25]). amplification (adopted from Wijk et al. [25]).
As shown in in Figure Figure11, 11,path path s represents represents the thereduction reductionfrom from O0 to that is, is, from from ((u0,, w0)) to As shown to s A ,, that to s is translated from s to S, that is, from u , w to u , w . Wijk and Nuij completed ((u0 ,, wm )).. Path ( ) ( ) m B 1 1 1 Path is translated from to , that is, from ( , ) to ( , ) . Wijk and Nuij path optimization work basedwork on the above-mentioned basic principles, as shown in following completed path optimization based on the above-mentioned basic principles, asthe shown in the equations [25]: following equations [25]: u0 , s ∈ [0, s A ) , ∈ [0, ) (12) u(s) = ⎧ wm (sρ−s A ) + u0 , s ∈ [s A , s B ) ( − ) ( )= + , (12) u1 , s ∈ [s∈B [, S], ) ⎨ , ∈ s[ ∈ ,[0,] s ) ⎩ w0 exp(ρs), A w(s) = (13) wm , ( ) , s ∈ [∈ s A[0, , sB ) ) w exp(, ∈ [ , ) ( )= (13) ρ(s B − s)), s ∈ [s B , S] m ( − ) , ∈ [ , ] ln wwm 0 s = A ρ ⎧ = ρ(u −u ) (14) ⎪s B = s A + w1 0 , ( m ) = + wm , (14) ⎨ S = s B + ln w1 ρ ⎪ = + where, u(s) means to pan along a straight⎩line, and wm = max w0 , w1 , ρ2 (u1 − u0 )/2 . ρ depends on the user’s(subjective feelings, and when the value of ρ is different, different when ) means to where, pan along a straight line, and = ( the, moving , ( path − is )/2). depends moving from point A to feelings, point B, and gapthe is more on the user’s subjective andthe when valueobvious. of is different, the moving path is different summary, based smooth and the efficient proposed by predecessors [25,26], whenInmoving from pointon Athe to point B, and gap isP&Z moremethod obvious. we analyzed the visualization problem of TopolView in proposed SIN. To implement the TopolView In summary, based on theinteraction smooth and efficient P&Z method by predecessors [25,26], we analyzed the visualization interaction problem of TopolView in SIN. To implement the TopolView based on the P&Z method, we used the improved FDA and the FAT method described above. Next, we describe the specific implementation of GeoView and the TopolView. 4. Results
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based on the P&Z method, we used the improved FDA and the FAT method described above. Next, we describe the specific implementation of GeoView and the TopolView. 4. Results The purpose of this section is to describe the analysis of the validity and feasibility of the previously proposed model from both theory and simulation perspectives. Because the implementation mechanisms of the entity domain view and topology domain view are different, we introduce them separately. 4.1. GeoView Implementation For the entity domain of SINDVis, firstly, we introduce the experimental platform and the operating environment, and then carry out the implementation of the methods based on Cesium; the specific content is as follows. 4.1.1. Experimental Platform and Operating Environment The specific experimental platform and operating environment are as follows:
• • • • • • •
Operating system: Windows 8.1 Professional edition_x64; Processor: Intel (R) Core (TM) i7-4790
[email protected] GHz; Memory (RAM): 8 GB; Graphics: NVIDIA GeForce GTX 745; Local server: wampserver3.0.6_x64; Browser: Internet Explorer, Avast Secure Browser, Google Chrome; Development tools: Brackets, Atom, Adobe Dreamweaver CS6, Eclipse, Cesium.js.
4.1.2. GeoView Function Implementation As described in Section 3.2.1, we used the LEO satellite system as an example to determine the whole function of the system. It was assumed that the LEO satellite system consists of five LEO satellites and one ground station. The GeoView not only supports a 3D view display, but also supports 2.5D and 2D view modes, and users can switch between pages. Figure 12a shows the specific network form of the LEO satellite system from the ground station point, and the purple curve in the diagram shows the orbit of the satellite in the information system. When the satellite is operating in an effective range with the ground station, the satellite is connected with the station and the data is transmitted, as shown in the cyan line in Figure 12b. Figure 12c shows the 2.5D view, and Figure 12d shows the 2D view, in which the purple curve is the orbit of the satellite. Based on LEO satellite information system, an MEO/LEO satellite system based on MEO/LEO constellation can be realized by increasing the MEO constellation. In this section, six MEO satellites were added to construct the MEO/LEO satellite information system based on the LEO satellite information system, as shown in Figure 13. As shown in Figure 13, the green curve is the orbit of the MEO satellite in Figure 13a, and it shows the satellite layout and the specific distribution of the MEO constellation. When the MEO satellites and LEO satellites run into a valid range, they are connected to each other for data transmission. The green line in Figure 13b shows that the MEO satellite and LEO satellite are transmitting data. Based on the above-mentioned system, we built the integral satellite information system by adding the GEO satellite information system. By considering the characteristics of GEO satellites, we used three GEO satellites, evenly distributed in the GEO orbit, to establish full coverage of the GEO satellite information system, as shown in Figure 14.
information system, as shown in Figure 13. As shown in Figure 13, the green curve is the orbit of the MEO satellite in Figure 13a, and it shows the satellite layout and the specific distribution of the MEO constellation. When the MEO satellites and LEO satellites run into a valid range, they are connected to each other for data transmission. are Electronics 2018, 7,The 316 green line in Figure 13b shows that the MEO satellite and LEO satellite 18 of 25 transmitting data.
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(d) (d)
Figure 12. The The view view display display of of the the LEO LEO satellite satellite information information system: (a) (a) The The specific specific network network form of of Figure Figure 12. The view display of the LEO satellite information system: (a) The specific network form of the LEO satellite system from the ground station point; (b) the satellite is connected with the station the LEO satellite system from the ground station point; the satellite system from(c)the ground point; (b) theinformation satellite is connected the station andLEO is transmitting; transmitting; 2.5D of the the LEO LEO satellite information system; (d) (d)with 2D view view the and the data is 2.5D view station of satellite system; 2D of the and the data is transmitting; (c) 2.5D view of the LEO satellite information system; (d) 2D view of the LEO satellite information system. LEO LEO satellite information system.
(a) (a)
(b) (b)
Figure 13. The 3D view display of the MEO/LEO satellite information system: (a) The satellite layout Figure The 3D 3D view display of the MEO/LEO MEO/LEOsatellite satellite information information system: (a) (a) The The satellite satellite layout layout Figure The and the13. specific distribution of the MEO constellation; (b) the MEO system: satellite and LEO satellite are and the the specific distribution distribution of of the the MEO MEO constellation; constellation; (b) (b) the the MEO MEO satellite satellite and and LEO LEO satellite satellite are and transmitting data. transmitting data. transmitting
Based on the above-mentioned system, we built the integral satellite information system by In Figure 14, above-mentioned the yellow curve system, is the orbit of thethe GEO satellite, and information Figure 14a,bsystem show the Based on the weconsidering built integral satellite by adding the GEO satellite information system. By the characteristics of GEO satellites, we connections between theinformation GEO satellites and the data transmission status of GEO-2 andsatellites, the ground adding the GEO satellite system. By considering the characteristics of GEO we used three GEO satellites, evenly distributed in the GEO orbit, to establish full coverage of the GEO station named The purple line in the diagram is the transmission link. Thus, now, we have used three GEOBS. satellites, evenly distributed in the satellite information system, as shown in Figure 14. GEO orbit, to establish full coverage of the GEO established the satellite information system of the SIN. Compared to the four-story structure of the satellite information system, as shown in Figure 14. Near Space layer, due to its particular structure and location and the page range limitation of the SINDVis system, the specific network situation is not clear in the overall view of Near Space.
transmitting data.
Based on the above-mentioned system, we built the integral satellite information system by adding the GEO satellite information system. By considering the characteristics of GEO satellites, we used three GEO satellites, evenly distributed in the GEO orbit, to establish full coverage of the19GEO Electronics 2018, 7, 316 of 25 satellite information system, as shown in Figure 14.
(a)
(b)
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Figure 14. 14. The The 3D 3D view view display display of of the the GEO GEO satellite satellite information information system: system: (a) (a) The The connections connections between between Figure the GEO andand the ground station. the (b) to theits data transmission statusand of GEO-2 Near Spacesatellites; layer, due particular structure location the page range limitation of the
SINDVis system, the specific network situation is not clear in the overall view of Near Space. Next, wewe use an theGEO concrete network theNear Near Space layer In Figure 14, the yellow curve is the to orbit of the satellite, andofof Figure 14a,b show the Next, usethe theHABs HABsasas anexample example to display display the concrete network the Space layer information system. For terrain complex areas, people can only rely on the Hab group to complete information system.the ForGEO terrain complexand areas, can only relystatus on theofHab group to the complete connections between satellites the people data transmission GEO-2 and ground thethe task. Therefore, we terrain complex mountainous areaasasthe thebackground background environment, task. Therefore, wechose chosethe the terrain complex mountainous area station named BS. The purple line in the diagram is the transmission link. Thus, environment, now, we have with 12 HABs forming a group, as shown in Figure 15. with 12 HABs forming a group, as shown in Figure 15. established the satellite information system of the SIN. Compared to the four-story structure of the
Figure15. 15.The The3D 3Dview viewdisplay display of the Near Figure Near Space Spaceinformation informationsystem. system.
AsAs shown theballoon balloonmodel model Cesium library, a balloon swarm shownininFigure Figure15, 15, by by loading loading the inin thethe Cesium library, a balloon swarm is constructed with in in thethe green box as as a data is constructed with 12 12 balloons. balloons.We Weselected selectedthe theballoon balloonsurrounded surrounded green box a data transmission centerthat thatcan canconnect connectwith withthe the ground ground station station and transmission center and 11 11other otherballoons. balloons. sumup, up,combining combining the of of SIN andand the function of view GeoView in the entity ToTo sum thearchitecture architecture SIN the function of in view in GeoView in the domain, we constructed the GeoView. The GeoView and TopolView complement each other, and entity domain, we constructed the GeoView. The GeoView and TopolView complement each other, mainly demonstrate thethe specific composition andand structure of of thethe SIN from thethe physical entity and mainly demonstrate specific composition structure SIN from physical entity perspective to let users have an intuitive visual experience of SIN. Meanwhile, the web-oriented perspective to let users have an intuitive visual experience of SIN. Meanwhile, the web-oriented model model developed in thisispaper more popular and more convenient for Internet-based users.Based Basedon developed in this paper moreispopular and more convenient for Internet-based users. on Cesium.js for the display of entity domain view of SIN, there many ancillary functions can be Cesium.js for the display of entity domain view of SIN, there many ancillary functions can be developed. developed. The purpose of this section was only to carry out mapping with the SIN architecture and The purpose of this section was only to carry out mapping with the SIN architecture and the basic the basic functions of GeoView. Its subsidiary functions will be further developed in future studies, functions of GeoView. Its subsidiary functions will be further developed in future studies, and we and we have not elaborated on them too much in this section. have not elaborated on them too much in this section. 4.2. TopolView Implementation
4.2. TopolView Implementation
For the topology domain of SINDVis, firstly, we introduce the experimental platform and the For the topology domain of SINDVis, firstly, we introduce the experimental platform and the operating environment. Then, we carry out the implementation of the methods from the layout, operating environment. Then,perspectives. we carry out implementation of the methods from the layout, visualization and interaction Thethe specific content is as follows.
visualization and interaction perspectives. The specific content is as follows. 4.2.1. Experimental Platform and Operating Environment
The specific experimental platform and operating environment are as follows:
Operating system: Windows 8.1 Professional edition_x64; Processor: Intel (R) Core (TM) i7-4790
[email protected] GHz;
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4.2.1. Experimental Platform and Operating Environment The specific experimental platform and operating environment are as follows:
• • • • • • •
Operating system: Windows 8.1 Professional edition_x64; Processor: Intel (R) Core (TM) i7-4790
[email protected] GHz; Memory (RAM): 8 GB; Graphics: NVIDIA GeForce GTX 745; Local server: wampserver3.0.6_x64; Browser: Internet Explorer, Avast Secure Browser, Google Chrome; Development tools: Brackets, Atom, Adobe Dreamweaver CS6, Eclipse, D3.js, Vis.js, Echarts.js, Cytoscape.js.
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4.2.2. TopolView Function Implementation
4.2.2. TopolView Function Implementation
As described in Section 3.2.2, we show the overall structure of the SIN in the topology domain; As described in Section 3.2.2, we show the overall structure of the SIN in the topology domain; that is, the entity and connection relationships are mapped to the nodes and the edges respectively to that is, the entity and connection relationships are mapped to the nodes and the edges respectively show their relational structure. to show their relational structure. Corresponding to Section 4.1.2, it is assumed that the SIN consists of the following components: Corresponding to Section 4.1.2, it is assumed that the SIN consists of the following components: three GEO satellites (ref.: GEO_1~GEO_3), six MEO satellites (ref.: MEO_1~MEO_6), five LEO satellites three GEO satellites (ref.: GEO_1~GEO_3), six MEO satellites (ref.: MEO_1~MEO_6), five LEO (ref. LEO_1~LEO_5), 10 hot air balloons Hab_1~Hab_10) and twoand ground stationsstations (ref.: F_1~f_2). satellites (ref. LEO_1~LEO_5), 10 hot air(ref.: balloons (ref.: Hab_1~Hab_10) two ground (ref.: This is in accordance with others in terms of the connection rules. A formation schematic diagram of F_1~f_2). This is in accordance with others in terms of the connection rules. A formation schematic thediagram initial topology is shown in Figure 16.in Figure 16. of the initial topology is shown
(a)
(b)
(c)
(d)
Figure Theprocess processdisplays displays of of dynamic dynamic networking elements of of SIN at the Figure 16.16.The networkingofofSIN: SIN:(a) (a)The Thebasic basic elements SIN at the initial moment;(b) (b)the theformation formationprocess process of of the the MEO/LEO-layer MEO/LEO-layer satellite (c)(c) thethe formation initial moment; satellitesystem; system; formation process satellitesystems; systems;(d) (d)the theprocess process of of prototype prototype formation process ofof satellite formationofofSIN. SIN.
Figure 16 shows the dynamic networking of SIN in the SINDVis system from a topology domain perspective. Based on the architecture of the SIN that was discussed earlier, the basic elements of the SIN, including the GEO, MEO and LEO satellite systems and ground stations, are presented at the initial moment in diagram (a), and we assume that the internal connection relationship is established. Figure 16b demonstrates the process of connecting the MEO satellite system and the LEO satellite system to form a MEO/LEO-layer satellite system. Figure 16c shows a three-layer, interconnected SIN
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Figure 16 shows the dynamic networking of SIN in the SINDVis system from a topology domain perspective. Based on the architecture of the SIN that was discussed earlier, the basic elements of the SIN, including the GEO, MEO and LEO satellite systems and ground stations, are presented at the initial moment in diagram (a), and we assume that the internal connection relationship is established. Figure 16b demonstrates the process of connecting the MEO satellite system and the LEO satellite system to form a MEO/LEO-layer satellite system. Figure 16c shows a three-layer, interconnected SIN consisting of the GEO-layer satellite system, the MEO/LEO-layer satellite system, and the ground station, and to solve the problem of the Near Space layer, the Hab group is added to represent the Near Space layer information system. As shown in Figure 16d, the Near Space layer information system is connected to the entire network, and then the prototype of SIN is formed. Next, we show the specific evolution of the SIN TopolView and demonstrate the dynamic interaction capabilities of the SINDVis system. In Figure 17, Figure 17a shows the interactions between the user and the node. When the user Electronics 2018, 7, x FOR PEER REVIEW 21 of 25 puts the mouse over a node, the details of the node appear at the top right of the page, including the node name, name, node node degree, degree, output output stream, stream, and and input input stream. stream. The The detailed detailed information information is is hidden hidden when when node the mouse mouseisismoved. moved.Figure Figure 17b shows interactions between the edge. When the the 17b shows thethe interactions between the the useruser andand the edge. When the user user puts the mouse over a connecting edge, information about the edge of the details, including the puts the mouse over a connecting edge, information about the edge of the details, including the target target node and the source node’s name and the connection level appear in the upper right of the node and the source node’s name and the connection level appear in the upper right of the page. The page. The detailed information hidden theismouse is Figure moved.17c Figure 17cashows a translation detailed information is hidden is when the when mouse moved. shows translation of the of the interactive function. To display only the details of the GEO layer on the page, the other interactive function. To display only the details of the GEO layer on the page, the other parts ofparts the of the network be translated outvisual of the page. visualFigure page. 17d Figure 17d ashows zoom function based on network can be can translated out of the shows zoomafunction based on Figure Figure 16d, that is, it displays details on the same size page by scrolling the mouse to zoom in the page. 16d, that is, it displays details on the same size page by scrolling the mouse to zoom in the page.
(a)
(b)
(c)
(d)
Figure 17. Interactive function (a)(a) thethe interactions between the user and Figure function displays displaysofofthe theSIN SINTopolView: TopolView: interactions between the user the node; (b) the between the user theand edge; the translation interaction function; and the node; (b)interactions the interactions between theand user the(c)edge; (c) the translation interaction (d) the zoom interaction function. function. function; (d) the zoom interaction
By combining the content shown in Figures 16 and 17, the partial functionality of the TopolView for the SINDVis system can be described as a whole, as follows:
Description 1: Both of Figures 16d and 17a are views with the same network structure, and due to the limitations of the network structure itself, it is difficult for a user to understand the four-
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By combining the content shown in Figures 16 and 17, the partial functionality of the TopolView for the SINDVis system can be described as a whole, as follows:
•
•
•
Description 1: Both of Figures 16 and 17 are views with the same network structure, and due to the limitations of the network structure itself, it is difficult for a user to understand the four-layer architecture of the SIN through Figure 16d. Therefore, we constrained the network nodes at different levels by introducing clustering coefficients. For the four-layer structure in SINDVis, the effect of Figure 17a is achieved by setting four different constraint values. After the constraint with the clustering coefficient, the network composed of four circular faces was included in the network nodes of the respective level, a clearer level display was realized without affecting the network’s overall topology structure. Description 2: In combination with Figure 10 in Section 3.4.3 above, we used a timeline-based approach to accomplish animation control of the SINDVis system, as shown in Figures 16 and 17 on the bottom, right corner of the page. We set the animation time zone to [0, 12], and carried out an animation demo in two ways. One way was through the mouse drag slider, according to the needs of users in real-time animation conversion. The other was by clicking the “Play/Pause” button to achieve an automatic display of animation. Meanwhile, in order to achieve a friendlier function design and meet the needs of more users, we added acceleration/deceleration control buttons to the timeline module. Description 3: In order to highlight the differences in the importance levels of different nodes in the whole network, we used area coding to display the different degree values of the network nodes in TopolView. A big degree value corresponds a large area, or vice versa. Of course, given the limited scope of the view page, the node degree values mentioned above are relative values. Meanwhile, given the directionality of data transmission in the network, we used color-coding to show the differences between inputs and outputs, as shown in the gradient red and gradient green in the Figure.
To sum up, by combining the architecture of SIN and the function of the TopolView in the topology domain, we constructed the TopolView. TopolView and GeoView complement each other, and mainly demonstrate the dynamic topological evolution laws of SIN from the topology perspective. Meanwhile, the web-oriented model developed in this paper is more popular and more convenient with Internet-based users. The TopolView shows the dynamic networking process of the SIN from scratch, and we integrated the users’ needs into the view page and achieved real-time interactions with users. Figure 17 can also be used to understand the increases and deletions of the nodes and edges mentioned above, but this paper does not show the specific details. The main purpose of this section was to demonstrate the basic functionality of TopolView, and more versatility will be developed based on this view. 5. Discussion This article focused on designing and implementing a user-centered interactive visualization system, SINDVis. The system abandons the traditional C/S architecture and satisfies many kinds of user needs in web-oriented form. The users of the SIN can be broadly divided into three categories based on their sources and characteristics. Firstly, there are people who are interested in SIN but know little about it. The second includes users involved in the design and construction of SIN. The third is that of users involved in the management and maintenance of SIN. Due to the difference of background knowledge and expertise of different users, we proposed designing the main view of the system as the entity domain view GeoView and the topology domain view TopolView together to meet the different needs of many users. In the theory and method analysis, combined with the characteristics of SIN, we designed the SINDVis architecture and elaborated on the various functions of GeoView and TopolView. For the view realization, we emphatically discussed the TopolView realization method,
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including improving the FDA layout and proposing a FDA layout method, as well as proposing and analyzing the FAT and P&Z methods. For the entity domain, GeoView, we showed the process of dynamic networking of SIN from the perspective of the entity domain. This included the operation and networking of different levels of the information system. By combining this with the architecture of SIN, finally, users can realize the initial understanding of the SIN. To determine the advantages and disadvantages of the STK, SaVi, and SINDVis, we performed a comparative analysis of four aspects: architecture, service type, interactivity, and scope. The details is shown in Table 3. Table 3. Simulation platform contrast analysis in the entity domain. Name
Architecture
Service Type
Interactivity
Scope
STK SaVi SINDVis
C/S C/S B/S
Heavy-weight Light-weight Light-weight
Weak Weak Strong
Commercial software Research software Comprehensive software
For the topology domain, TopolView, we showed the process of dynamic networking of SIN from the perspective of the topology domain. The included the increase of nodes and edges, the establishment of the connection, and the real-time operation of the network. Meanwhile, we focused on the realization of a real-time interactive view function for users. The development process of the visualization system was a continuous iterative process. The user-oriented visualization system was based on the analysis of the user’s initial requirements, and through the design of its basic functions, the design and realization of the initial SINDVis was completed. Based on the initial version, through users’ continuous use, combined with their feedback, suggestions, and comments, we will improve the system. Through continuous modifications, trials, feedback, new requirements and recommendations, we will develop useful SINDVis and products. Therefore, the most important factor is the development of the user-centered SINDVis, and only the users can know what their purpose is based on the SINDVis. In addition, timely and effective communication between developers and users is the precondition and foundation to ensure the continuous optimization of the SINDVis. 6. Conclusions 6.1. Summary As a national infrastructure, SIN has important significance for the military and for people’s livelihoods, and it also has become a hot research field in recent years. In order to allow the effective construction and efficient management of SIN, we applied the relevant technology and methods of visualization to the SIN. Meanwhile, a user-centered interactive visualization system for SIN was designed and implemented based on the topology domain view and entity domain view to meet the multiple needs of multi-class users. By designing the SINDVis architecture and then directing the system to design, and by describing the different functions of the views, we presented the validation indicators for the SINDVis. In the concrete realization of the method, we can draw on its successful application in other fields, but also combine the characteristics of the SIN to improve and optimize it. Finally, the results not only satisfied the described functions of GeoView and TopolView, but also verified the validity and feasibility of the proposed and related theories and methods. 6.2. Limitations As we know, although we designed the SINDVis, and displayed and analyzed the results through a typical SIN, we think that there were the following insufficiencies in our study.
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2.
3.
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In order to illustrate the problem and simplify the operation, we controlled a certain small range of SIN (26 nodes, 58 edges) in the case description. However, the real network is much larger and more complex, and how to achieve a clearer display based on this system is not mentioned in this article. This study was implemented only to determine the underlying functionality and achieve a preliminary view display. Therefore, the integrity of the system was weakened during validation and the SINDVis system is not a complete system that can be used by users at its current stage. System development is a continuous iterative process, and we only constructed the SINDVis system based on the users’ initial requirements. At present, there is no mature product can consider the users’ real-time operation and use requirements. Whether the SINDVis can better achieve the different functions of users’ needs to be researched and demonstrated at a later stage. Meanwhile, we also improve and optimize the system in the future.
6.3. Prospect Combined with the research contents and shortcomings of this paper, future studies will be carried out based on existing research, as follows. 1.
2.
3.
Reasonable layout and integration of GeoView and TopolView. That is, we aim to achieve a reasonable layout of the two views in one interface. One view is primary, the other is supplemented, and a smooth conversion between the main and secondary views is possible. Increasing the interactive operation modules of GeoView and TopolView. For example, the operation modules in the GeoView of the user should include the addition or deletion of entities according to a user’s own needs, changes in the entity running track, and so on. The operation modules in the TopolView of the user should include the addition or deletion of nodes and edges, changes in the scope of the local-world, and so on. This will allow users to achieve better understanding, control, and management of SIN. Constructing the primary version of the SINDVis system for users and collecting feedback and suggestions from different users to upgrade and optimize the system. Through a number of trials, feedback and optimization, the final version SINDVis system should be able to meet the needs of multi-class users.
Author Contributions: S.Y., X.Z. and X.M. completed the overview; S.Y. and L.W. structured the theory and method; S.Y. accomplished the verification of results; L.W. and P.C. helped with the verification; S.Y. wrote the paper. X.Z. and X.M. helped with writing. Funding: This work was supported by the Equipment Pre-Research Foundation under Grant No. 6142010010301. Conflicts of Interest: The authors declare no conflicts of interest.
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