Spatial Information Retrieving Using Internet

SETIT 2005

3rd International Conference: Sciences of Electronic, Technologies of Information and Telecommunications March 27-31, 2005 – TUNISIA

Spatial Information Retrieving Using Internet Asli Garagon Dogru*, Gonul Toz**, Haluk Ozener* *

Bogazici University, Kandilli Observatory and Earthquake Research Institute, Geodesy Department, 34684 Cengelkoy Istanbul, Turkey [email protected] [email protected] **

Istanbul Technical University, Civil Engineering Faculty, 34469 Maslak Istanbul, Turkey [email protected]

Abstract: The primary view of geographic data has historically been through maps. Now, the rise of the Internet has allowed to provide geospatial data through online mapping interfaces. A Geographic Information System (GIS) is an organized collection of computer hardware, software, geographic data, and personnel designed to efficiently capture, store, update, manipulate, analyze, and display many forms of geographically referenced information (ESRI 1995). Together with the use of the Web, GIS allows public to access GIS functions and data. WebGIS is described as a network-centric tool that uses “the Internet” to access and transmit data and “analysis tools” to enhance the visualization and integration of spatial data. This study represents an access to earthquake information and interactive database applications with querying capabilities over the Internet. In this study, data acquired from different sources were compiled by using GIS softwares. WebGIS software packages provide the various kinds of GIS functions and analysis. This study has implemented with the MapObjects Internet Map Server. Key words: Earthquakes, GIS, Information retrieval, Internet/Web.

1 Introduction The spatial information is being shared over the Internet. Through distributed geographic information, users have easy access to large databases. Internet technology and GIS provides a group of advantages to simplify the management and to access to the information. This paper tries to explain how can spatial information be disseminated to end users with low technological requirements by using internet technology. Data used in the study is earthquakerelated spatial and also non-spatial data. A M=7.4 earthquake hit Izmit, northern Turkey, on August 17, 1999. 17.000 people were killed, 44.000 people were injured, 73.000 buildings were collapsed, 16 million people and 10 cities (64,000 km2 area) were effected, surface fault rupture was 110 km. After this catastrophic earthquake, public attention is more focused on earthquakes. This study provides public access to earthquake information and interactive database applications with querying capabilities over the Internet.

2 Spatial Data on the Internet 2.1 web-based GIS Web-based GIS applications are becoming an important tool to disseminate geographical information on the Internet because of their platform independence, interactivity, and wide accessibility (Hu 2002). Geographic Information can be distributed in any form over the Internet such as static map images, simple map services, or advanced GIS. Nevertheless, web applications are based on the same model called client/server (Plewe 1997). The client makes a request to a server. The server processes the request and returns the information to the client. In this model, the process is shared between the client and the server, with different ratios. This sharing process is generated in various forms which have advantages and disadvantages. A thick client interacting with a light server provides powerful analysis. But it is hard to maintain the service. A thin client interacting with heavy server is limited with simple applications. However, it can be used by many people. In this study server-side architecture was choosen to perform basic GIS operations (Figure 1).

SETIT2005

Figure 1: Server side model 2.2 components of an online system The implementation of Internet GIS requires not only network infrastructures to disseminate geospatial information, but also software architecture to provide interactive GIS functions and applications (URL 2004). Figure 2 shows the major components of any online database system.

Figure 2: Components of online databases (Polley 1998) ESRI’s MapObjects and MapObjects Internet Map Server (MOIMS) are used as development tools for building a Web-based GIS for geospatial information retrieval. The IMS provides the WWW data server requirements for users, accepting requests for data from users and subsequently making requests of a data server. It receives requests from web pages through the HTTP server. Subsequently, it interacts with a data server, then passes the retrieved data back to the users computer. The data server is provided by a MapObjects application. MapObjects is a developer environment with a number of ActiveX components that allows developers to build their own data server, based on the MapObjects components. This allows standard basic functionality but with custom implementation to suit the developer's needs (Polley 1998).

3. Case Study 3.1 method, tools, and data The Dynamic (Real-Time) Map Browser technology was chosen to implement the application (Figure 3).

Figure 3: System architecture The study provides access to very large spatial databases and allow users to browse GIS functions (such as display, query, retrieve, and update maps on line) without having to own special hardware or software (besides a browser and internet compatible computer) (Chang 1997). Users can turn on/off thematic layers on the web page to set up the environment for mapping. Users can also click buttons to start display commands such as zoom in, zoom out, identify, pan, etc. The requests from user will be sent to the server side. A gateway at the web server passes the request to a GIS server (MOIMS). Then it generates a graphic file that will be converted to a JPEG image. The JPEG image is later sent back to the client and viewed by the users with a standard web browser. Steps of retrieving information from the server can be summarized as follows: – Process preset parameters for mapping. – Make the map and translate it to a BMP file. – Translate the BMP file to a JPEG file. – Serve the image by HTML. The WebLink control method BMP2JPEG of MOIMS generates a JPEG file given a source BMP file. This format reduces the size of the image data and thus reduce the time required to send the data across the Internet. HTML is used to implement simple controls for manipulating the map. In order to listen requests from the users, WebLink ActiveX Control is used. WebLink has a method called WriteString that is used to create HTML. MapObjects provides the following functions (ESRI, 1996c): Map Drawing – Display a map with multiple map layers, such as roads, rivers and boundaries. – Pan and zoom throughout a map. – Draw graphic features such as points, lines, circles and polygons. – Draw descriptive text. Feature Selection – Identify features on a map by pointing at them. – Select features along lines and inside boxes, areas, polygons, and circles. – Select features within a specified distance of other features. – Select features with an SQL expression. Spatial Querying and Statistics – Calculate basic statistics on selected features. – Query and update attribute data associated with selected features. – Render features with thematic methods such as value maps, class breaks, and dot density.

SETIT2005 – Label features with text from field values. Image Integration – Draw images from aerial photography or satellite imagery. Event Tracking – Dynamically display real-time or time-series data. Geocoding – Type in an address and find a location on a map. The map control is the main object of the MapObjects. The map control is a container for the maps (Figure 4). Maps are displayed on this container. A programmer may either create a DataConnection object and use it to connect to a database to find GeoDataset objects, or may interactively select data through the map control's property sheet. Following is the codes for adding layers to the application: ‘ add shapefiles Dim dc As New DataConnection Dim Lyr As MapObjects2.MapLayer dc.Database = ImsDataPath If Not dc.Connect Then MsgBox “ims_data set not found” End End If Set Lyr = New MapLayer Set Lyr.GeoDataset = dc.FindGeoDataset("Roads") Lyr.Symbol.SymbolType = moPointSymbol Lyr.Symbol.Style = moSquareMarker Lyr.SymbolColor = moRed Lyr.Symbol.Size = 9 Lyr.Visible = False Map.Layers.Add Lyr

– Add fields and attributes data For the preparation of the spatial data ArcView, ArcInfo, Erdas Imagine, and Microsoft Photo Editor programs were used. Digital Elevation Model downloaded from the US Geological Survey’s web site were exported to cell based grid format. ArcView was used to classify grid data according to its height values. In order to use raster data in MOIMS application, data were converted from grid format to JPEG image format. And then it was converted to Tagged Image File Format (TIFF) using Microsoft Photo Editor software. Because MapObjects displays TIFF format more efficiently than JPEG format. For population density map, ArcView and it’s scripting language (Avenue) were used to calculate areas of the boundary polygons and colorize shape file according to the population density values. Population values of districts were added to districts dBASE table. Density image was exported to JPEG format. And then JPEG file was converted to TIFF format. Current Eartquakes and Historical Earthquakes layers were symbolized using their magnitude and depth values. Other vector layers were symbolized with single values. In the study, vector data format is ArcView shape file format (shp). Vector data (downloaded from http://www.gisdatadepot.com - Digital Chart of the World’s web site) were acquired in shape file format. For other ASCII text files which include coordinate information of stations and earthquake parameters information, ArcView scripting was used to convert text file to shape file format. All of these data were in geographic coordinates relative to the WGS-84 and ED-50 datums. Datum transformations and coordinate conversions were performed. Data were projected to Lambert Conformal Conic map projection. ArcView can not export maps to georeferenced images. So topographic map image and population density map image were georeferenced to the Lambert Conformal Conic projection by using image processing software ERDAS Imagine. Spatial data is shown in figure 5.

Figure 4: Visual Basic project with components Raster and vector, the two types of geographic data were prepared using GIS softwares. Raster data is a cell based data structure composed of rows and columns. Vector data represents each feature as a row in a table, and feature shapes are defined by x,y locations in space. For combining multiple files on the same display, data must be in the same spatial reference system. The process to prepare data for the Web-based GIS application is as followed: – Data conversion – Coordinate transform

Figure 5: Spatial data in the same spatial reference system Current earthquakes layer is the dynamic layer in the study. Microsoft Internet Transfer Control and a Timer Object were used as components to update the current earthquake information. The timer control that runs at intervals is used to update the current earthquake information. In every ten minutes, the

SETIT2005 application connects the URL address http://www.koeri.boun.edu.tr/sismo/trk.txt using the Microsoft Internet Transfer Control. After the connection, the text file that contains current earthquake information is downloaded from the web page. The downloaded text file is stored in a string variable. This file includes date, time, latitude, longitude, depth, magnitude and location information of the earthquakes. Using this information a new point type geographic dataset is created and the old layer is removed. Point coordinates of the earthquakes are in the geographic coordinate system. They are converted to the Lambert Conformal Conic Projection by using a dll program which was created with C++ programming language before. The projected coordinates are stored in the shape file and attributes are stored in the database table (Garagon 2002) (Figure 6).

Figure 7: Session management (Marshall URL) The web page contains an interactive map container which displays the map layers, and a legend column. The toolbar column is used for setting parameters and controling layers, and the legend column is an explanatory table of the symbols appearing on the map (Figure 8).

Figure 6: Update process 3.2 retrieving spatial and attribute information The URL address for the Web-GIS application: http://ServerName/scripts/esrimap.dll?Name=MapServ iceName&Cmd=Map The syntax that is used in URL includes three parts: .dll, name, and cmd. The first query parameter in the URL is used to determine which application the client wants to communicate. The application name follows the “?” sign. Each argument and value pair is seperated with “&” sign. Arguments and values are used to call the functions that perform specific mapping operations. In this URL address, “Name” is the argument and “MapServiceName” is the value. Arguments transmit the information to the application that which function will be executed by the GIS application. Values are the parameters for these functions. Session management is a critical part of any multiuser application. It is the key to performing the correct task for the right user. A MapObjects application is designed to run as a single-user application (it uses a single threaded ActiveX control) so when accessed by multiple users in a Web environment, the requests are queued in a single thread. This means that a user's request will have to wait for previous requests to complete before beginning execution (Marshall URL). As a solution we designed the system to return each request to the correct application (Figure 7).

Figure 8: Client side of the application Zoom In, Zoom Out, and Pan are the basic visualization functions for most GIS. Zoom In provides a simple way for users to see more detailed spatial information. To make the Zoom In function work, select the Zoom In radio button and click on the map. Pan is a function for moving the display area of spatial data by clicking a point. The centroid of the map will move to the new point. Identifying a feature map by clicking on a location of interest will bring the end users the attribute data. Combo boxes, check boxes, and radio buttons are used for the user interaction. Full Extent button handles a full display of a map. Thumbnail map helps orientation. Figure 9 shows the GIS operations.

SETIT2005 information will take some time for communication between the client side and the server side. There will be subsequent improvements in the techniques to make it more efficient. The study is made up of overlapping and inter-disciplinary categories. So new datasets and functions can be added to the service. In summary, the technologies related to the Webbased GIS applications include Object-Oriented Language, GIS package and language, HTML, and CGI. The softwares used to develop this application include: MapObjects, MapObjects Internet Map Server, Visual Basic, Microsoft Internet Information Server, and ArcView. Figure 9: GIS operations

Conclusions The study includes many types of data and algorithms from the field of geosciences, computers, GIS, networking and databases. In the study, several software tools are used for processing input data, storing them in a database and presenting on the web. A GIS application and a web site were developed to serve the system on the Internet. This study represents the interactivity of the Internet users and the spatial data. Online GIS applications have interactive interfaces that include graphic and text-based retrieval of data. By means of this study, the various type of collected information can be disseminated to end users with low technological requirements. Web clients can be any standard Web browsers that support HTML such as Microsoft Internet Explorer. The Web server and the mapping application may reside on different machines, allowing mixed configurations. In this study, single computer configuration was choosen (Figure 10).

Figure 10: Single computer configuration The system to create the application includes: Platform: PC Processor: Intel Pentium 4 CPU 2.40 GHz Operating System: Windows XP V.2002 Disk Storage: 120 GB Memory: 1 GB Server: Microsoft Internet Information Server Network: 3com Gigabit LOM (3C940) Information will be available for several different types of user. The solution performance can be changed according to the needs of the user by simply reconfiguring the server. The approach to access

Acknowledgment The authors would like to thank Professor Dr. Onur Gurkan for his consultation and Taner Selcuk for his support on this study.

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