A Survey of Stereoscopic Visualization Support in - CiteSeerX

To appear as: Bektas K., Coltekin A., 2009. " A Survey of Stereoscopic Visualization Support in Mainstream Geographic Information Systems", Proceedings, True 3D in Cartography, 1st International Conference on 3D Maps, Aug. 24 - 28, 2009, Dresden, Germany (refereed extended abstract)

A Survey of Stereoscopic Visualization Support in Mainstream Geographic Information Systems Kenan Bektaş and Arzu Çöltekin {kenan.bektas, arzu.coltekin}@geo.uzh.ch Geographic Information Visualization & Analysis (GIVA), Department of Geography University of Zurich – Irchel, Switzerland

Abstract. Principles of stereoscopic vision have long been used in geographic data processing and visualization, e.g. Laussedat created what he called metrophotography in 1895 [2][3] and a stereoautograph for plotting from terrestrial photographs was produced in 1911 [2]. Today, a common and established use of stereoscopy in geographic domain is three-dimensional (3D) modeling of terrains and cities based on aerial, satellite and/or terrestrial imagery with photogrammetric techniques. In these systems, commonly, stereoscopic imagery is used as an input and a vector 3D representation of the terrain or city is obtained as an output. Stereoscopy has also been used for close-range photogrammetry, however within the scope of this paper the focus is on the cartographic use of stereoscopic visualizations. In recent years, a number of mainstream digital devices with stereoscopic capabilities are marketed (e.g. [4], [5], [6]), which indicates that we can expect to see more stereoscopic content in the near future [1]. In anticipation of such a development, it is also plausible to expect that stereoscopic geo-data will become more available for everyday use. It is, therefore, interesting to document which stereoscopic visualization features are supported by mainstream geographic information systems (GIS) software and whether these features can be improved. This work presents a survey on current stereoscopic visualization support in geographic information (GI) systems. The underlying objective is to outline future research needs by examining current stereoscopic 3D visualization techniques and tools in current GISs. This paper focuses on visualization modules of GIS software, and tries to answer the question “How commonly is stereoscopic visualization supported in GIS?" To achieve this, first whether such support exits or not in GIS software is documented, then supported types of stereoscopic operations and viewing methods are reported. Motivated by improving efficiency of stereoscopic visualizations in cartographic domain, within this survey, it is also examined whether these software offer level of detail (LOD) management support for stereoscopic datasets. Findings from the study are meant as a guide to researchers and practitioners to assess the current state of True 3D support in widely used GIS software. Keywords: Stereoscopic visualization, True 3D, GIS software, Survey, Cartography, Photogrammetry, Level of Detail (LOD)

1. Introduction and background The term visualization expresses forming a mental or computational picture of something which is not actually present to the sight and stereoscopy, in its traditional sense, is the art and practice of using stereoscope as a tool. Combining the two; stereoscopic visualization describes the concept or process of creating an image by the help of a stereoscope or using stereoscopic principles in a digital environment. The word stereoscope is coined by Sir Charles Wheatstone (1838) [2][7] and according to Oxford English Dictionary (OED) it is “an instrument for obtaining, from two pictures of an object, taken from slightly different points of view, a single image giving the impression of solidity or relief, as in ordinary vision of the object itself” [7]. Although early methodic investigation on geometric analysis of images can be traced to late 15th century by Leonardo di ser Piero da Vinci [2] in Italy, the definition of stereopsis (as the ability of perceiving depth with stereoscopic vision) and invention of stereoscope has been in Victorian era in 1838 [2][7] in the United Kingdom. Successively, in 1895 Aimé Laussedat constructed a metric camera that he called metrophotographic, for making photogrammetric measurements [2][3] in France. Later in 1911 Orel and Zeiss produced the stereoautograph for plotting from terrestrial photographs [2]. The growing interest in the domain has led to the foundation of International Society for Photogrammetry and Remote Sensing (ISPRS) in 1910 and American Society for Photogrammetry and Remote Sensing (ASPRS) in 1934 [2][8]. In the last two decades significant developments in sensor (optics, electronics) and computer (hardware and software) technologies have opened new ways to further improve methods and application areas of photogrammetry and remote sensing. Today photogrammetric techniques are used in many fields spanning from astronomy, archeology, medicine, entertainment, forestry, environmental engineering and cartography among others. As a brunch of Surveying (today frequently referred to as Geomatics) Photogrammetry has consistently provided various types of information for GIS databases since its beginning [2]. GIS software is defined as “software to create, manage, analyze and visualize geo-referenced information” [9]. Dr. Roger Tomlinson developed the first operational geographic information system in 1962 [13]. Over time GIS received wide acceptance in research, education, governing as well as industry [13][15]. A constant trend in producing cheaper and more powerful hardware [10][11] has led to implementations of even more robust GIS software. GIS experts predict that developments in GIS and online geographic information tools such as virtual globes will have a similar positive impact on GIScience as the personal computers have made in computer science thirty years ago [16] [41]. The combination of the Internet and spatial technologies allowed for the development of more recent concepts like Geoweb and virtual globes (e.g. Google Earth, NASA World Wind or Microsoft Bing Maps) [16]. While virtual globes are not a substitute to GIS, they offer useful and interesting geographic information and services to very large audiences, hence making the GI technology and products more mainstream [17].

GISs have come a long way since 1960s, but as technology continues to become cheaper and more available, the demand for spatial data and services in everyday life also gains momentum. Driven by this demand, a number of studies are conducted in a variety of domains to make GISs even more efficient and effective. There is significant progress in processing and visualization of geographic information [2][23][26] as well as in other information visualization applications [4][5][6][27]. Among several methods that have been developed for visualizing geographic information more efficiently, a useful concept springing from computer graphics is called level of detail (LOD) management. While managing the LOD the software and/or the content provider takes practical and perceptual constraints into account in rendered and visualized scenes [18]. In principle, a complex object is constructed and stored at different resolutions and the most appropriate representation is chosen in real time in order to address the tradeoff between image fidelity and frame rate [12]. LOD management techniques can also be found in Cartography and GI literature in recent years [31][32][34]. In vector environments, LOD management methods often involve simplifying complex polygonal meshes, in raster environments, LOD management typically occurs in controlling the resolution of the imagery to match the computational needs and human perception. The selection of higher or lower resolution representations of the appropriate portion of the same object can depend on several factors including: the distance of the object form the viewpoint, the size of the object on the screen space, the eccentricity of the object with respect to the user's gaze, the velocity of the object across the user's visual field, the priority of the object according to the user's interest [12], or for stereo rendering also the depth of field where the user's eyes are converging [29][30][36]. Basic principles behind LOD were first described by James Clark in 1976 [14]. Clark proposed a hierarchical scene graph structure as he recognized the redundancy of using many polygons to render an object covering only a few pixels. Beginning in early 1990s more researchers have become interested in describing algorithms for simplifying a highly detailed model while protecting the visual appearance [12]. LOD management is especially important for low bandwidth environments, such as web based real-time applications and other environments where visualization of realistic 3D geographic information is on demand, such as mobile devices and car navigation systems [19][20][24][26][28]. To obtain a set of different resolution levels of raster datasets, there are a number of approaches using different methods to build what is often referred to as image pyramids (see Figure 1). MIP mapping (from first letters of Latin phrase: multum in parvo, meaning much in a small space) [38], for example, is a simple texture filtering technique supported by many graphics hardware. MIP maps represent textures using an image pyramid in which each cell is typically an un-weighted average of the corresponding cells in the next finer level of the pyramid [12]. The Multiresolution Seamless Image Database (MrSID) is a wavelet based image encoding technique, where for every image a number of multi-resolution zoom levels are created, and corresponding file format developed by LizardTech for its GeoExpress product which is primarily designed to support GISs [21].

Figure 1: An example of an image pyramid. To the right, 6 levels of detail can be seen. Original aerial photograph by Wolfgang Pehlemann, 2008, showing Frauenkirche in Dresden, Germany (licensed under the Creative Commons Attribution ShareAlike 3.0).

LOD management offers several advantages, one of which is that it provides a strong compression. For displaying large geo-datasets in virtual environments (geovirtual environments), LOD management is often critically important [31]. To describe the visual

experience in virtual environments the term “True 3D” has also been used. The expression True 3D is slightly more encompassing than “stereoscopic display” as it is used to refer to all kinds of 3D visualizations that create an immersive experience for the viewers (including stereoscopic displays and holograms) [23][25][35]. In such systems (as in stereoscopic viewing), the displayed virtual scene or object is perceived in front or behind the physical screen which allows the 3D experience to be more true. LOD management in True3D has been studied less than in other graphics environments for its computational complexity and smaller market. However the market for True3D is growing (e.g., [4][5][6]) and this motivates further research into concepts and techniques to enhance the experience. This paper is motivated by a larger research project that is concerned with LOD management in handling stereoscopic 3D geoinformation. The next section will present a survey about the capabilities of mainstream GIS software in stereoscopic visualization and LOD management. Following this, a basic scoring scheme is presented for evaluating the results. Finally concluding remarks and future directions are offered.

2. Software survey 2.1. Method and criteria To establish the state of the art on any given subject, a literature review is the common practice. A (non-comprehensive) literature review is provided in the previous chapter. Additional approaches include expert interviews (an online questionnaire has also been launched and is in progress) and in case of technical subject, a documentation of features implemented in most common software in the domain can help guide the researchers and developers [37][40]. This paper reports the results of a survey that scans through a number of GIS software, selected based on literature [9] and their market share [33]. Included software are; ESRI’s ArcGIS, Intergraph’s GeoMedia, ERDAS, Autodesk’s AutoCAD, Bentley’s MicroStation, Pitney Bowes’ MapInfo, Quantum GIS (QGIS) and GRASS. Stand-alone photogrammetric software are not evaluated in this study, as one of the objectives is to document whether some traditionally photogrammetric methods are integrated in GIS software. A modern GIS is expected to cope with imagery and contain modules for all stages of handling 3D geo-objects, even though these are traditionally considered photogrammetric tasks [39]. In the selected software, a number of modules were surveyed for a number of features to document the current status in widely marketed and used GIS software. Following specific questions were formulated for a systematic evaluation: Does the software support 3D visualization? If yes, does it support it internal or external module (i.e. is it built-in the software, or do they use a third party software for it)? Does the software support stereoscopic visualization? If so, is it natively (internal) supported or does it use an external (third-party) module to do this? Documenting whether such support exists or not, it is possible to deduce how commonly 3D and stereoscopic visualizations are used across the surveyed GIS platforms. A further step at this stage is to establish what kind of stereoscopic viewing these software allow (active or passive). Some forms of stereoscopic viewing require intense computational interaction with complex hardware via a dual-head graphics card, therefore this could be interpreted as an indicator of the effort the GIS software developer invests. This can be viewed as a further indication of demand, hence acceptance of stereoscopic visualization methods in GIS community. Findings from the first steps lead to another question: if the GIS software supports stereoscopic visualizations, does it have some built-in algorithms to compress the data “on the fly” or rather, in other words, does it support some form of raster LOD management? To answer these questions; software manuals, GI and Photogrammetry journals and news resources were reviewed, and when this was not sufficient, companies were contacted via phone and email to get more insight into their solutions.

2.2. A detailed documentation of the software and relevant features on stereoscopic visualization 2.2.1.

Environmental Systems Research Institute (ESRI) ArcGIS

ESRI was founded in 1969 and provides a set of GI software across platforms which are very widely marketed and has a large userbase. ArcGIS 3D Support. In ERSI’s ArcGIS suite, 3D data handling and analysis module is 3D Analyst. 3D Analyst is able to handle large sets of (in terabytes) 3D vector or raster data (i.e., terrain and/or image data from a local or global perspective) via ArcGlobe™ application. ArcScene™ application allows user to view GIS data in 3D and is used as the viewer module for 3D Analyst. In stereo viewing mode in ArcScene, it is possible to use anaglyph (requires red/blue or red/green glasses) or shutter glasses (requires a set of additional hardware) as well as stereo free viewing (no additional wear is necessary) 3D Analyst supports all data formats used in ArcGIS, including several image formats, Shapefiles, geo-database and other CAD data. In addition to these, 3D Analyst supports MultiGen, OpenFlight and 3D Studio MAX formats which allows for a more realistic representation of 3D features. Beside calculations of area, volume, slope, aspect and hillshade, an interactive and seamless navigation through multiresolution image data is also

supported. Creating animations is also possible in 3D Analyst using flight paths, and key frames in MPEG, AVI or QuickTime format. Additional features like distance-dependent drawing and LOD support gives user further control over 3D visualizations. Raster Pyramids are reduced resolution representations of spatial data used to improve visualization performance. In ArcGIS family, Raster Pyramids concept corresponds to raster LOD management, as its use allows visualizing different levels of details depending on scale. 3D Analyst is highly integrated with ArcGIS geo-processing framework and can be used with ModelBuilder™ to build complex 3D models. A style library is also provided including more than 500 real-world symbols (e.g., houses, cars, plants etc.) in 3D format, enhancing scientific visualization and simulation of the real world [42][43]. ArcGIS Stereo Support. While ArcScene has native stereoscopic visualization support, additional stereoscopic operations within ArcGIS is possible by installing an external module called Stereo Analyst developed by Leica Geosystems. Stereo Analyst is capable of collecting and revising spatial features from imagery in a stereoscopic environment. Besides supporting ArcGIS Editor Toolbar, stereo advanced editing tools, grid tool, 3D measurement tool for slope, length and heights, 3D position tool for driving to a location are some of the other tools integrated to Stereo Analyst which increase the user control over data collection operations. Stereo Analyst is able to update existing datasets with 2D to 3D feature conversion tools. Adding Z values from digital elevation models (DEMs) or triangulated irregular networks (TINs), updating existing Z values, unit conversion for Z values, virtual 2D to 3D mapping and 3D to 2D conversion are some of the operations handled by Stereo Analyst. Stereo Analyst can access oriented images using advanced standard data server ArcSDE, and is able to work integrated with ArcView, ArcEditor and ArcInfo. It also uses ArcCatalog to handle photogrammetry projects and to preview the connected images. Stereo Analyst supports several image triangulation package formats. Raw data is imported from photogrammetry project files and some other supporting files containing information about the sensor. There is also a Component Object Model (COM) application programming interface (API) which enables other photogrammetric project formats. Some other features provided by Stereo Analyst are: Auto-loading adjacent stereo pairs into Stereo View, synchronizing Stereo View and ArcMap document displays, inverting Stereo Pair, orienting ArcMap document to Image Pair, selecting Stereo Pair from ground point selection in ArcMap document, brightness, contrast and dynamic range adjustments, and zooming to data extend or user defined scale. Stereo Analyst is automatically able to identify the graphics card in the system. If the graphics card does not support quadbuffered stereo, Stereo Analyst displays the image in anaglyph (red-blue), otherwise the image appears gray. If graphics card supports quad-buffered stereo, scene can be viewed with polarized or shutter glasses in 3D. Stereo Analyst supports standard system mouse and several 3D mice for substantial 3D work [44]. 2.2.2.

Intergraph GeoMedia

As a product of Intergraph Corporation (founded in 1969), GeoMedia is a set of integrated applications specialized for geographic information processing including data analysis, data sharing and map production [45]. GeoMedia 3D Support. 3D visualization modules in GeoMedia are TerraExplorer Pro, TerraBuilder and TerraGate. TerraExplorer Pro, a part of GeoMedia Product Suite, is developed by Skyline Software Systems as a standalone application allowing users editing analyzing, and annotating (e.g. text, labels, graphics, 2D and 3D entities) on spatial data and developing interactive 3D terrain visualizations. Latest release of TerraExplorer 5.1.2 (as of August 2009) has visualization and analysis features including: interactive drawing, importing and adding geometric shapes, user defined objects, text and labels on 3D terrain models, measurements for terrain analysis, creating snapshots, creating 3D Fly-through and movies in AVI format for flight paths and the Imagery Layer feature that enables to view multiple resolution levels of terrain imagery. Image Layer mechanism is also used to rectify source image files (e.g. Windows Bitmap (bmp), Tagged Image File Format (tiff), Graphics Interchange Format (gif), Joint Photographic Experts Group (jpeg), jpeg2000 formats) to the coordinate system used in TerraExplorer. Additionally an application programming interface is provided for developers to create extensions accessing external data sources [45][46][47][48]. TerraBuilder creates photo-realistic 3D terrain databases using aerial photos, satellite images, geographic terrain information, digital elevation models and vector data. It can support and import a wide range of image formats including: .gif, jpeg, jpeg2000, tiff, bmp, .img, user defined binary raw, MrSID compressed (.sid), Enhanced Compression Wavelet (.ecw). TerraBuilder is able to merge data of different resolutions and sizes and re-project them into a common reference projection where color adjustment, area selection and clipping operations are additionally available. Resulting 3D databases can be enhanced with 2D and 3D dynamic or static objects and streamed over internet or accessed offline [47]. TerraGate is the specialized application for streaming 3D terrain data over network to remote TerraExplorer users. It offers an optimized data transfer for low-bandwidth connections and works compatible with TCP/IP protocols, Secure Socket Layer protocol, firewalls and proxy servers, and takes the advantage of multi-processor server hardware [48]. On June 17, 2009 in international user conference of GeoMedia it has been announced that a new product "GeoMedia3D" is planned for 2010. GeoMedia3D will have 3D visualization capabilities integrated natively on GeoMedia [49]. GeoMedia Stereo Support. ImageStation Stereo, the registered product of Z/I Imaging Corporation (acquired by Intergraph in 2002 [63]), is the GIS based feature collection environment for GeoMedia. ImageStation Stereo is able to capture, display and manipulate 3D photogrammetric and remote sensing data. ImageStation Stereo uses GeoMedia data servers to access common databases (e.g. Oracle Spatial, SQL Server or ArcSDE). Data collection can be also interactively handled in stereo modus. Generated data can be stored in an open database so that third-party GIS systems can access it for any geospatial application. ImageStation Stereo supports compressed and uncompressed 8-bit gray scale and 24 bit Red Green Blue (.rgb), jpeg and tiff formats. ImageStation Stereo offers dynamic zoom and automatic raster enhancement, interactive feature extraction and geometry validation capabilities as well as infrared shutter or passive stereoscopic viewing [40]. Dynamic zoom capability simulates the continuous optical zoom behavior of a stereo plotter

[64][65]. ImageStation Stereo supports infrared shutter and passive stereoscopic viewing. Their ImagePipe software enables stereo roaming. Company presents this concept as a means to eliminate stop-and-go image roam performance and it is suggested that it helps against the consequential operator fatigue [64]. 2.2.3.

Earth Resources Data Analysis System (ERDAS)

The Earth Resources Data Analysis System (ERDAS) Inc. was founded in 1978 and rebranded by Leica Geosystems Geospatial Imaging in 2008 [50]. Erdas 3D support. ERDAS Imagine is the raster graphics editor and remote sensing solution from ERDAS Inc. Some of the other solutions of ERDAS Inc. in photogrammetry and geographic information visualization fields are: Leica Photogrammetry Suite (LPS), Imagine Vector, ERDAS Image Compressor, ERDAS Virtual Explorer, ERDAS Imagine Stereo Analyst and ERDAS Imagine VirtualGIS. ERDAS Imagine VirtualGIS is an extension to ERDAS Imagine, and it is able to create, analyze, and visualize 3D geographic representations. Users can project aerial or satellite images and airborne scan data on to terrain models and add vector layers, symbols and 3D objects to enrich the visualization. Creating 3D movies, animating objects and navigating through scenes is possible using VirtualGIS. An additional feature for providing seamless visualization during zooming operations is also included and it called multi resolution morphing. VirtualGIS supports DEMs from US Geological Survey (USGS), Digital Terrain Elevation Data (DTED) from National Geospatial Intelligence Agency (NIMA) and Defense Mapping Agency (DMA), OpenFlight databases, raster surfaces interpolated from ASCII or vector sources, and native DEMs of Imagine's OrthoBASE. It is also possible to drape 3D raster and vector formats in VirtualGIS Aerial photography, satellite imagery, scanned maps and thematic images are typical raster data resources for draping operations, and among the example vector formats, it is possible to list ArcInfo coverages, Shapefiles, ARCSDE, Open 3D Shapefiles [51]. ERDAS Stereo Support. Stereo Analyst, also a Leica product, is the solution ERDAS Imagine utilizes for data collection, interactive analysis (with 3D measurement and 3D position tools) and visualization operations. Stereo Analyst superimposes existing 2D vector layers onto a Digital Stereo Model (DSM). DSM can be created in four different ways; 1) Creating a relative stereo pair by overlapping, leveling, and projecting corresponding images 2) By using Create Stereo Model tool, which makes use of internal camera parameters and image information 3) By using external aerial triangulation results from photogrammetric systems 4) Using LPS which transforms raw data obtained from images to geo spatial information for photogrammetric operations such as producing orthophotos, terrain models and extracting 3D features. Spatial and non-spatial information can be modified by Stereo Analyst to achieve an accurate collection of 3D data. Stereo Analyst supports ESRI 3D Shapefiles and can transform 2D Shapefiles to 3D Shapefiles using DEMs as a vertical reference source. 3D perspective (supported by OpenGL) and stereoscopic 3D views can be displayed at the same time. In addition to anaglyphs, stereo emitters and stereo graphics cards, are some of the hardware supported by Stereo Analyst. Image enhancement capabilities of Stereo Analyst include: brightness and contrast adjustments, image histograms, stretching and scaling operations. For image handling and visualization performance hierarchical pyramids layers are used. In addition to Stereo Analyst LPS Stereo is an add-on that can be combined with LPS or PRO600 (introduced in more detail in section 2.2.5) for extracting geospatial content using stereoscopic images [52].

2.2.4.

Autodesk AutoCAD

Autodesk was founded in 1982 and offers CAD and GIS solutions, best known for their product AutoCAD in GI community. AutoCAD 3D Support. AutoCAD Map 3D 2010 is the solution of Autodesk Inc. built on AutoCAD platform for creating, analyzing and managing 3D spatial information. Map 3D is able to project aerial photographs on to topographic data and works with more than 4000 real-world coordinate systems by offering transformations between them. Survey functionality, map creation and stylization, data integration and management, creation of 3D surfaces via Surface Creation extension, surface analysis including elevation, aspect and slope analysis as well as 3D visualization and shading studies are some of the operations offered by Map 3D. Developers can further extend the functionality by custom tools and applications using PHP, Java and .NET APIs provided by Autodesk. Map 3D is able to work with vector, raster and tabular data in several formats. Supporting open source Feature Data Object (FDO) technology Map 3D also extends data access for developers. Using FDO technology Map 3D supports ESRI Shapefile, Oracle, Microsoft SQL Server, MySQL and ESRI ArcSDE managed databases. In addition to bmp, jpeg, tiff, DEM, and Portable Network Graphics (.png) raster formats, sid, ecw and jpeg000 are additional supported types for streaming and visualization of multiresolution images [53]. AutoCAD Stereo Support. In terms of stereoscopic visualization, one native and two external software are supported by Autodesk products. LandXplorer is the 3D city modeling software of Autodesk Inc. It can create, analyze and visualize digital city models. In addition to 3D visualization capabilities, LandXplorer offers stereo viewing of digital models with well-suited 3D hardware and shutter, polarized or anaglyph glasses. Two other photogrammetric software are also compatible with AutoCAD. ELCOVISION 10 is one of the third-party photogrammetric software supported by Autodesk, developed by PMS Photo-Mess-Systeme AG. This close range photogrammetry package has several modes that enable 2D digital rectification, stereoscopic measurements and stereoscopic visualization via anaglyph or LCD shutter methods [54]. Super/Imposition (hardware and) the other third-party software system from

DAT/EM Systems International supported by Autodesk, which is a graphics tool that allows stereo-plotter operators to perform map revisions using digitized objects superimposed on stereoscopic models [55]. 2.2.5.

Bentley MicroStation

Bentley Systems Inc. was founded in 1984 and provides CAD and GIS solutions among other software. MicroStation is their main product for geo-spatial operations. MicroStation 3D Support. In geospatial imaging division Bentley Inc. offers two products relevant to this survey. Bentley I/RAS B is the module that handles raster-vector conversions. Bentley Descartes on the other hand, is highly integrated with Bentley's 2D and 3D design tool MicroStation. Bentley Descartes can create seamless mosaics of multiple images, scanned aerial photos or adjacent raster scanned images. It can also convert between raster and vector formats and between different coordinate systems. Using WYSIWYG (What You See is What You Get) tool image registration verification the transformation of vector data on uncorrected images is possible. Bentley Descartes supports binary, grayscale and 1 to 64 bits color image formats where conversion between those formats is also possible. ecw (optimized for aerial and satellite imagery), sid (for multiresolution images), img, jpeg2000, 1 to 32 bit tiff, rgb, and bmp are some of the data formats supported. In addition to tools which are able to crop, copy, move, merge, scale, mirror, square and rotate images, there are options to make images translucent or transparent. Bentley Descartes can then project those images on a Digital Terrain Model (DTM) or on 3D objects by using real life textures and applying lighting effects. Creation of fly-through animations and 3D 3D Portable Document Format (PDF) are additional visualization features. Developers may use the Bentley Descartes API to develop batch applications that can automate repeatable operations [56]. MicroStation Stereo Support. Stereoscopic feature collection and visualization support for Bentley's MicroStation is provided by Leica PRO600 package (also known as ERDAS PRO600) which is developed by authorized Bentley partner ERDAS. Leica PRO600 provides a stereo viewing engine, data collection and editing tools, in addition to a feature definition library. It is closely integrated with LPS and user defined functionalities may also be added via Visual Basic macros or advanced C/C++ applications. PRO600 package supports Leica TopoMouse and other 3D input devices and consist of several add-on modules including: PROCART, PROLPS, PRODTM, TerraModeller and LPS. These add-ons provide cartographic functionalities, linking between modules, creation of workflows for terrain modeling applications, displaying terrain models and photogrammetric operations respectively. Integrated with LPS, PRO600 supports active and passive stereoscopic viewing [57]. 2.2.6

Pitney Bowes MapInfo

MapInfo Professional is the mapping and geographic analysis application marketed by Pitney Bowes Inc. MapInfo 3D Support. Vertical Mapper module, integrated within MapInfo Professional, has map creation, analysis and 3D rendering features and it mainly works on grid-based continuous spatial information. Vertical Mapper can create continuous surfaces from point data; and contour, slope and aspect maps with relief shaded surfaces. By means of Grid Translator Pro (GTP) add-on from Geomatics Systems, Vertical Mapper can import around 60 raster formats (e.g. bmp, img, gif, jpeg, and Silicon Graphics Image (sgi)) to Vertical Mapper's grid format and export Vertical Mapper grids to standard raster formats. Vertical Mapper has a Software Development Kit (SDK) which allows developers to implement additional functionalities [58]. Encom, acquired by the Pitney Bowes in December 2007, develops custom-build extensions for MapInfo Professional. Encom Engage 3D pro is one of these tools which handles 3D vector and raster data analysis and visualization. Encom Engage 3D pro performs a number of tasks including surface creation, analysis and interactive presentation (via fly-throughs) of spatial data. In addition to these tasks, additional features such as smoothing and clipping, creation of color look-up tables, adding transparency and lighting effects, image format conversion are provided. As an optional module of Encom Discover, the Encom Discover 3D is fully integrated with MapInfo, handling both 2D and 3D modeling and visualization tasks. Draping raster images on to 3D surfaces, real-time navigating in 3D and full-color 3D stereo projection with dual graphics card support are some of the features of Discover 3D [59][60]. MapInfo Stereo Support. Stereoscopic 3D support module for MapInfo is Encom Discover 3D. This module supports dual-head graphics cards and therefore full color 3D stereo projections are possible. Discover 3D can handle 3D Connexion’s SpaceNavigator™ 3D mouse [60].

2.2.7

Quantum GIS and Grass

These two open-source GIS software are commonly used and share some modules, therefore are reported in the same section. Quantum GIS (QGIS). QGIS is an official project of Open Source Geospatial Foundation (OSGeo) designed as a GIS with GNU General Public License. QGIS can be installed on Microsoft Windows, Mac OS X, and Linux platforms. QGIS is able to maintain common GIS task including editing, analysis composing and visualization of spatial data. It is also possible to develop customized GIS applications using QGIS library, C++ and Python languages. Geospatial Data Abstraction Library (GDAL) is a translator library

(licensed by Open source Geospatial Foundation) for raster and vector geospatial data formats [61]. GDAL support means that QGIS can handle raster and vector data formats. The GRASS plug-in in QGIS provides access to GRASS GIS database and functionalities including visualization of GRASS raster and vector layers, digitizing vector layers, editing vector attributes, creating new vector layers and analyzing GRASS 2D and 3D data with GRASS modules (more information about GRASS modules and GDAL supported image formats can be found in the next paragraph). In QGIS for visualization performance, level of detail management is handled by creating and storing lower resolution copies of data, creating a pyramid. Depending on the level of zoom (i.e. scale) most suitable layer of resolution can be selected from this data pyramid. Scale dependent rendering (i.e. visibility of a layer) allows user to specify a threshold for minimum and maximum scales on which a layer will be visible. By controlling map rendering option the visibility of a layer can also be suspended. There are sample applications for Quantum GIS where 3D spatial data is created in LPS and can be visualized via GRASS plug-ins [22]. Geographic Resources Analysis Support System (GRASS). GRASS is an open source GI-System used for management, analysis and visualization of geospatial data, as well as image processing, map production, and modeling purposes. GRASS binaries can be installed on Mac OS X, Microsoft Windows and Linux [62] platforms. Although there is a graphical user interface (GUI) provided for a number of operations, GRASS user has to use various types of commands (basically the commands are names of modules developed for certain tasks) with some additional parameters. There are over 300 core modules in addition to 100 add-on modules developed by users with C, C++, Python, UNIX shell, Tcl or other scripting languages. GRASS has 2D and 3D raster map processing, vector processing image processing, visualization and animation modules. For example r.in.gdal module is used to import a GDAL supported raster file (around 80 formats are supported including tiff, bmp, jpeg, jpeg2000, gif, png, and sid) into a binary raster map layer. v.in.org module is used to convert GDAL/OGR vector layers to GRASS vector map. nviz animation and visualization module is used to visualize raster and vector data for rendering 3D surfaces and has color, lighting and transparency adjustment capabilities. Users also have control over resolution to refine rendering speed and level of detail. The tcl/tk interface is planned to be rewritten to allow developers add more functionality to nviz. By using ppmtorgb3 and rgb3toppm commands, it is possible to create a stereo anaglyph image in nviz. Furthermore Paraview ( an open-source multiplatform data analysis and visualization application) can also be used to render anaglyphs by exporting GRASS data with r.out.vtk, r3.out.vtk and v.out.vtk commands [62].

3. Results The results of GIS software survey are presented on Table 1. Mainstream GIS software vendors provide support for both 3D and stereoscopic visualization. The investigation of the company strategies shows that these either provide individual solutions like ESRI or ERDAS, cooperate with external software companies like Intergraph uses Skyline solutions or acquire an external software company giving geo-visualization solutions like Encom has joined to Pitney Bowes Inc. or Z/I Imaging Corporation to Intergraph.

 

3D Visualization  Support 

Stereo Visualization  Support 

Active/Passive Viewing 

LOD 

ESRI 

ArcGIS 3D Analyst 

ArcGIS Stereo Analyst 

Anaglyph, polarized  stereo emitter, shutter glasses 

Raster Pyramids,  MrSID 

Intergraph 

TerraBuilder, Terra  Explorer, TerraGate 

Imagestation Stereo for  GeoMedia 

Passive system, Infrared  emitter, shutter 

Imagery Layer Feature,  MrSID 

ERDAS 

ERDAS IMAGINE  VirtualGIS 

ERDAS IMAGINE Stereo  Analyst 

Anaglyph, polarized  stereo emitter, shutter glasses 

Multi Resolution  Morphing, Hierarchical  Pyramid Layers, MrSID 

AutoDesk 

AutoCAD Map 3D  2010 

LandXplorer  ELCOVISION  10  Super/Imposition 

Anaglyph polarized, shutter 

MrSID 

P600,       Super/Imposition 

Anaglyph, polarized  stereo emitter, shutter glasses 

MrSID 

Encom Discover 3D  supports stereo  projection 

Full‐color 3D stereo projection 

Preview Resolution,  MrSID 

Bentley 

Pitney Bowes 

Bentley Descartes  integrated with  MicroStation  MapInfo Vertical  Mapper, Encom  Engage 3D and  Discover 3D 

Quantum GIS 

GRASS modules 

GRASS modules 

GRASS modules 

Scale Dependent  Rendering, MrSID 

Grass 

nviz module 

ppmtorgb3 and  rgb3toppm commands 

Anaglyph 

LOD, MrSID 

Table 1. Results of the GIS software survey.

3D/Stereo/raster LOD support 

In the first column selected GIS software is listed, other columns present 3D visualization, stereoscopic visualization and LOD management supports of these software respectively. The second column shows that all software provide either a native 3D visualization solution (e.g. ESRI, ERDAS, AutoDesk, Bentley, and Grass) or use an external implementation (e.g. Intergraph, Pitney Bowes, and Quantum GIS). Raster and vector formats are supported by all products and some of them allow conversion between these data formats (e.g. ESRI, ERDAS, Bentley and Pitney Bowes). As it is presented in the third column, all GIS software provide stereoscopic visualization support to some extent. In this category one third of the GIS software is supported by Leica products including Stereo Analyst for ESRI and ERDAS and P600 for Bentley. Column four shows that passive stereoscopic viewing methods like anaglyphs or polarized glasses are supported by all of the software where active shutter systems are only supported by GIS solutions from ESRI, Intergraph, ERDAS, Autodesk and Bentley. Column five records the LOD support of GIS software listed in the first column accordingly. The interesting point here is that almost all software uses a different terminology explaining same concept, the LOD management. On the other hand, all software support the common multi resolution raster format MrSID. Putting the surveyed information together and scoring each supported feature, an overview can be obtained to better evaluate the results (Figure 2).

Evaluated GIS software 

Figure 2. Left: scoring the results: if a feature is present, it is graded as 1. Right: A chart showing the comparative results. The scoring scheme that is introduced in Figure 2 (left), works such that every supported feature gets 1 point. Following features are graded: 3D visualization support (1), stereoscopic visualization support (1), stereo viewing (anaglyph (1), polarized (1), shutter (1)), LOD support (LOD implementation (1) MrSID (1)). A total grade is calculated for each evaluated software based on these scores. These results show that the leading commercial GIS software include operations that can handle 3D data, stereoscopic visualization, several formats of stereoscopic viewing and some raster LOD management. 4.

CONCLUSIONS AND FUTURE WORK

In 2002, Heipke noted that modern GIS software should contain modules that support all stages of handling 3D geo-objects, and noted that “systems available on the market are rather far away from this” [39]. Looking at the results of the presented survey, it possible to say that today largely marketed GIS software is better equipped for dealing with 3D geo-objects. The presented software survey provided a documentation which shows that mainstream GIS software extensively support 3D and stereoscopic visualizations either natively or by integrating a third party software. This can be interpreted as a concrete demand from GIS users for True3D visualizations. If the commercial companies invest in implementing or buying these systems, they must have clients who need these services. Along with the software survey we conducted a literature review which also shows that there is a growing interest in stereoscopic/True3D techniques in the domain. Additionally, an online questionnaire to measure expert attitudes and opinions working in geographic information research and practice has been launched and is in progress. Early results indicate that many of the participants find stereoscopy to be useful for geographic tasks. A detailed analysis from this questionnaire will be included in a followup publication. Considering these results, and the innovations in visualization hardware, we contend that further research to improve the effectiveness and efficiency of representations of complex geographic data taking human factors into account is a timely endeavor. The LOD implementations used in GIS software listed in this study mainly represent the spatial data for the sake of zooming operations, accounting for distance or size LOD. The surveyed software does not include other types of LOD management, e.g. priority type or depth of field. Introducing human visual system inspired LOD management methods into existing GIS systems, LOD management models and methods can be improved.

Acknowledgements. This research is funded by SNF project “GeoF: Development and implementation of Geofoveation” 200021_120434/1. We would like to express our gratitude to the company representatives who have made the time to speak to us about their products.

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