Transactions on Information and Communications Technologies vol 18, 1998 WIT Press, ISSN

Transcription

1 The development of web-based geographic information processing software K.S. Kim, M.S. Kim, K.W. Lee & J.H. Lee GIS Lab.,Systems Engineering Research Institute, #1 Eoeun Dong, Yusung Gu, Taejon, , South Korea {enoch, minsoo, kilee, Abstract Recently, Web-based Geographic Information Systems (CIS) with the rapid expansion of Internet and World Wide Web (WWW) is regarded as one of important issues for web application, and several GIS products running on web browser have been announced. However, most of these products have excluded spatial analysis functions to be one of the most important core parts of GIS's utilization, and offered SQL-based spatial data searching and the followed mapping on Web browser. Web-based GIS to be developed in this research provides spatial analysis functions as well as mapping and data searching, and can handle geographical features as geometric objects with associated topological relations and classification attributes. The basic structure of this system is the 3-tier database model which is composed of client, middle tier, and server. While, we defined three kinds of feature, which are node type, chain type, and polygon types. In this developed system, working area is divided into 3 classes, project, zone, and layer. Current main GIS's functions in this system are vector layer editing/error handling function, identifying, coordinate conversion, spatial query in access of DBMS, in/out zooming of vector layer on raster image, labeling, interested area exaggeration function, spatial statistics, and some spatial analysis functions. All of them are performed at the client. Spatial analysis functions in current version of this system are near, adjacency, containment, connectivity, in/out buffering, and shortest path searching. We developed webbased GIS using pure Java computing language. In this paper, we present the results of feature-based GIS running on WWW, as the experimental study at Taejon, composed of vector data sets and remotely sensed image.

2 334 GIS Technologies and their Environmental Applications 1. Introduction Nowadays, WWW or Internet environment changes not only the environment of computing but also the way people use the computer in business and the everyday life. The WWW(World Wide Web) to be based the Internet can be connected very easily from any place of globe. The users who access only a web browser can use easily the numerous kinds of service which are offered by a web site constructing on the Internet. According to the ease of access, many web application program to be based the Internet are made, and some researches for GIS-typed applet and/or application development are proceeding [1,2,3,4,5]. Like most of the Internet applications, Internet-based GIS, are based on the simple client/server model. In a client/server system, one computer acts as a client that sends requests to the server computer. The server computer processes the requests, and then sends back the results to theclient[2]. Some Internet GIS web sites to be built based on the client/server model are presented. Most of them, however, have offered the simple query and searching for map data or vector data in database, and the display to present the searched results. These systems have a restriction on the use and the extension, and could not be reflecting the various request of user, especially advanced users. In this study, we developed a geographic information processing software, which is one of the most important components in GIS: Human, Software, Hardware, and Data. As it is based on the Internet, the web user can access that from the whole world by using any kind of web browser. The software to be developed in this paper offered spatial analysis functions as well as mapping and data searching functions, and added the editing function such as insertion, deletion, and update to satisfy the various request of user. In our spatial information manage system, we defined the geographic features by using object-oriented technology. We used Java language which can process a dynamic interaction between the client and the user on the Internet and is standard for object-oriented programming within the Internet and Intranet.

3 GIS Technologies and their Environmental Applications Client/Server Architecture of 3-tier Model at Figure 1. The proposed client-server architecture in this study is represented Client: Web Browser Java Applet (Client Application) HTTP Server : Web Server and DB Web Server JavaClass Database JDBC Figure 1. Client/Server Architecture Internet GIS is designed using 3-tier database system configuration. At Figure 1, Java applet programs are transferred from web server to web browser and data sets are transferred from database driver through broker through broker system. This extra data transmission methodology solves the reconnection overhead of HTTP whenever web browser accesses data set. Web browser of client works a user interface and performs all spatial application programs. While, database server system connects to externally commercial programs, and commercial-based external database through JDBC library and manages a feature data set and spatial indexing information. To the end, broker system makes a data connection between server and client, and manages a multi-user access. Figure 2 shows detail functions of each client, broker, and server in developed 3- tier database model. The developed software in this study divided the role of the client and the server. In this environment, we reduced the load of the server and speed up the response time of the server.

4 336 GIS Technologies and their Environmental Applications Client GUI Spatial Analysis Refinement Query Processing Request Etc Borker Access ^ TCP/IP Port# w ^ Broker Receive Client Requests Access Server Database Reply server Result to Client Exception and Rules Handling Multi-user Access Processing A JDBC Socket T Port# Server Spatial/Aspatial Data Manage Spatial Indexing Manage Figure 2. Core functions of each client, broker, and server 3. The Client The client system is implemented by expanding an existing web browser and is made up of user interface manager, spatial application manager, and communication manager. User interface manager stands by user requests and displays some processing results. Spatial application manager performs spatial query or spatial analysis functions. Communication manager creates a connection to the broker system and receives data set from broker system. There are three kinds of working area in this proposed system: project, zone, and layer. The project is the whole area, the zone is selected area by user, and the layer is a selected feature set by user within the whole features. 3.1 GIS Functions The functions being offered by in current version of this system divided largely into 6 components: editing functions, data conversion functions, coordinate conversion functions, object identifying functions,

5 GIS Technologies and their Environmental Applications 337 spatial analysis functions, and miscellaneous functions [5]. (1) Editing functions : creating, deleting, moving, copying, and updating spatial object. (2) Data conversion functions : importing DXF, and exporting DXF (3) Coordinate conversion functions : converting coordinate among TM, UTM, and Geo Coordinate and the basic coordinate is TM. (4) Object identifying functions : selecting node object, chain object, and polygon object and information by using mouse. identifying each attribute (5) Spatial analysis functions : near, adjacency, containment, connectivity, in/out buffering, and shortest path searching. (6) Other functions : spatial query, zooming, labeling, spatial statistics, interested area exaggeration function, and so on. jfflgfflhsgpj! I Road»1 -Center J^J g ^j^^^^^ S<»^PoW(Mm^) EruiP(^(Mousa> m^tsf'iu^j^fks, gj (229229,317996) p;>^ ( ) """"""] Figure 3. Network Analysis : Finding Shortest Path

6 338 GIS Technologies and their Environmental Applications Figure 4. Spatial Analysis : In/Out Buffering 4. The Broker Avoiding over loading of HTTP (Hyper Text Transfer Protocol) and helping consistent large data loading jobs, this system designed and implemented broker system that make a connection to server database through TCP/IP. This broker system is previously operated, and stands by client request. When some client requests happen, the broker system works client connection, server database connection, and multiprocessing work. In order to create a connection to client system, broker has client access methods; Furthermore, client has broker access methods and all these access methods are made using TCP/IP socket program. In case of

7 GIS Technologies and their Environmental Applications 339 server database connection, JDBC (Java Database Connectivity) class methods are used to connect to external database. Broker system directly requests a query of SQL type and gets rapid responses through JDBC. Also, broker system creates a new thread to process a client system that newly requests a connection. 5. The Server Server database system manages all kinds of tables is server system such as spatial data table, non-spatial data table, feature definition table, and spatial indexing information table. Also, server system creates, updates, and destroys a spatial indexing for spatial data. In this system, we used R*-tree indexing methodology as indexing scheme and stored a indexing information at external database. In the result, server system is largely composed of DB Manager that manages all kinds of table, and Indexing Manager that manages R*-tree Manager performs insertion, deletion, update and indexing scheme [6]. DB retrieval functions through JDBC and database driver for spatial/non-spatial data and indexing information. Database driver is a program for establishing a connection between JDBC and database SQL. On the other hand, Indexing Manager creates and manages R*-tree indexing information. Indexing Manager, also, has import/export functions for database and write/read functions for file system because this indexing information is capable of being stored atfilesystem or database. 5.1 Geographic Features There are three kinds of geographic feature oriented towards object-oriented technology: node type, chain type, and polygon type. For instance, the node type's features are hospital, public building, gas station and other building. The chain type's features are highway center line and two kinds of road center lines. The polygon features are school, apartment complex, EXPO science complex park, inside building, and

8 340 GIS Technologies and their Environmental Applications institute. The element of geographic feature is represented at Figure 5 [5,7,8,9]. Figure 5. Composition of Geographic Feature 6. Conclusion In this study, we developed web-based GIS, being capable of easily carrying out advanced geographic processing by only using web browser. Since this system is fully developed with pure Java language, it fulfills Java's main advantage of platform independence. And 3-Tier database configuration easily makes the replacement of each component such as client, broker, and server. In other words, we are easily capable of satisfying with user by modifying only client system for user's request or functions; moreover, other applications based on GIS are possible at cost-effective level. Also when spatial analysis is executed, because filtering phase is executed in server and refinement phase is executed in client, this system reduces much load of server. This system can also handle satellite imagery in real application level, though just two functions such as vector layer overlay and new pixel manipulation are implemented in current version of this system. Some additional functions such as analysis result saving function, user accessible local function, and performance speed-up by improving database table structures will be developed soon. As further works or new research planning, we are in the middle of exploring actual Internet GIS application by using newly developed

9 GIS Technologies and their Environmental Applications 341 system with preprocessing modules and image processing modules of remotely sensed imageries. References [1] Qin Tang, Component Software and Internet GIS, GIS/LIS, [2] Burk torn as E. and Lime Stephen D., Internet Tools Complementing Local GIS Processing, Proc. GIS'97, pp , [3] Dai Qi, Evans Larry and Shank Mike, Internet Interactive GIS and Public Empowerment, Proc. GIS'97, pp , [4] Hawthorn R. Stuart and Engen P. David, Using the WWW for Spatial Systems Deplyment, Proc. GIS'97, pp , [5] Yue-Hong Chou, Exploring Spatial Analysis in Geographic Information Systems, On Word Press,1997. [6] N.B.Kriegel and B.Seeger, The R*-tree : An Efficient and Robust Access Method for Points and Rectangles, Proc. ACM SIGMOD Conf. Management of Data, pp , [7] MIL-STD 2407, Vector Product Format, Feature Class Relations, Appendix C, pp [8] Hanan Samet, The Design and Analysis of Spatial Data Structures, Addison-Wesley, [9] Agatha Y. Tang, Teresa M. Adams, and E. Lynn Usery, A spatial data model design for feature-based geographical information systems, International Journal of GIS, Vol.10, No.5, pp , 1996.