Home Articles Implementing Web GIS Applications using Open Source Software

Implementing Web GIS Applications using Open Source Software

V. Raghavan
Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka, Japan
Email : [email protected]

P. Santitamont
Survey Engineering Department, Chulalongkorn University, Bangkok, Thailand

S. Masumoto
Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka, Japan

K. Honda
ACRoRS, Asian Institute of Technology, Pathumthani, Thailand

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Introduction
Internet based geographical data services involve management spatial and non-spatial (attribute) data. Geographic Information System (GIS) has come to be an indispensable tool for analyzing and managing spatial data. Data pertaining to spatial attributes can be efficiently managed using Relational Database Management System (RDBMS). The development of a Web-based system by integrating GIS and RDBMS would serve two crucial purposes. Firstly it would allow the user to operate the system without having to grapple with the underlying intricacies of GIS and RDBMS technology. Secondly, it would allow sharing of information and technical expertise among a wide range of users. In the present paper we describe the salient features of spatial database that was developed by integrating the Open Source Software (OSS) GRASS GIS and PostgreSQL Object-Relational database into a Web based client/server environment. The system described in this paper aims at providing a web-based platform for collaboration and data sharing between specialists, planning agencies, citizens, and private entities. In order to access the spatial database, the user need only have a Web browser and access to the Internet. The system can be used to readily build and manage spatial databases pertaining to landslides (RAGHAVAN et al. 2001) and is presently being adapted to suit other applications such as a Water Infrastructure Inventory System (RAGHAVAN, HERATH & DUTTA 2001). Since the system is developed using OSS, it can be easily implemented in a distributed spatial database environment at a low overall cost. In this presentation we discuss salient features of an online system that offers public access to landslide information related to Japan (Japan Society of Landslides, 1996). The basic framework of the system is shown in Figure 1. Further, we also present an overview of our ongoing efforts to improve the interoperability and compliance with the OpenGIS Consortium (OGIS) Web Mapping Testbed (Web Mapping Testbed).

Figure 1 Components and Information Flow within the Prototype System
GIS Component
GRASS (Geographical Resource Analysis Support System) was used to provide the basic GIS framework. GRASS GIS was originally developed at the United States Army, Construction Engineering Research Laboratory. Presently, the development and distribution is coordinated by the GRASS Development Team index2.html) and is made available under the GNU General Public License (https://www.gnu.org). GRASS is a hybrid vector-raster GIS designed to provide digitizing, image processing, map production, and GIS system capabilities to its user. GRASS contains several routines for importing spatial data of a wide variety of commonly used formats. GRASS files can also be directly imported into many commercially available GIS packages or exported to suitable data formats. The spatial data included in prototype system consists of GRASS raster, vector and site data layers that provide the geographical reference.


 

 

RDBMS Component
RDBMS enables the fast storage and retrieval of large amounts of information. The interface that is used to insert, manipulate, and extract data is called the Structured Query Language (SQL). In case of the prototype system, the PostgreSQL database server has been used to manage the attribute data and multi-media content (e.g. image files). PostgreSQL is an Object-Relational DBMS, supporting almost all SQL constructs, including sub-selects, transactions, and user-defined types and functions. The database consists of tables that hold all the available attribute data. The attribute table includes fields that can be used to store binary data (images, multi-media contents etc.). Remote update of the database by permitted users is also made possible. An authentication mechanism to check which users can be allowed to enter new data or update the existing attribute data in the relational database is also provided.

Web Component
The system includes of two kinds of web interfaces that enable online access to the GIS layers and attribute information. Access to spatial data (GRASS database) is provided using the GRASSLinks interface (HUSE 1995) and PHP (PHP Hypertext Preprocessor) is used as an interface to access the attribute data (PostgreSQL). Since a majority of GRASS commands can be executed in the command mode, it is quite easy to enhance the GRASSLinks interface to provide added functionality to the system. In prototype system, several additional features were incorporated into the GIS web-interface to tailor the system for its present requirements. PHP is a server-side scripting language. PHP scripts are included within an HTML document to confer it the capacity of generating web contents on demand. Both GRASSLinks and PHP are distributed under the GNU General Public License and can be deployed on variety hardware platforms. PHP can be used to connect to several database engines such as PostgreSQL, MySQL etc.

System Features
An online demonstration of the basic features is available at -cu.ac.jp/slink/. “Spatial Query” option allows the user to retrieve attribute data from the RDBMS table by selecting a location on the raster image displayed on the web browser. The user selects the GRASS data layers from an interactive menu based on which the GRASS raster layer is displayed on the web-browser. The user can also select vector maps and site data as overlays for raster map layer (Figure 2). Interactive zoom/pan capability allows the user to view the displayed maps in greater details or to choose different areas for display. Once the desired area is displayed on the web-browser, the user is allowed to view the attribute table by “clicking” on respective site. The relation database is queried based on the geographical location (Figure 3a) of the “clicked” site. Attribute data is displayed in two stages. Firstly, a brief summary (Figure 3b) of the attribute information is presented. The summary table also includes a hypertext link, which can be followed to view more detailed information including figures and field photographs is also provided (Figure 4a and 4b).

Figure 2 Query basemap

Figure 3 (a) Location (b) Query results.

Figure 4 Detailed attribute information on individual landslide. (a-left, b-right)

“Database Search” option allows the user to retrieve attribute information by keyword searching (Figure 5). Search fields include name, location and date. In addition full-text searching is also provided. The results of the text based searching are the same as those shown in Figure 3b and Figure 4.


 

 

Project Case Study I – OYOGIS

Brief
To develop a desktop GIS application for managing geological/geotechnical information and integration with non-GIS based engineering applications.

Business Case
The requirement was to design and develop a GIS application to perform geological data analysis and extraction, enable visualization of geographic information, search and navigate through spatial data, and print customized reports including maps, graphics and tabular data. Specialized engineering modules such as the Bore-Hole viewer were developed and linked to the GIS application.

Scope of work

  • System Requirement Study.
  • System architecture and design.
  • Development and testing of the component.
  • Quality assurance and documentation.
  • User acceptance test.
  • Training for the system.

Technologies

  • ArcView-GIS Application Software
  • Trimble GPS Geo Explorer 3 and PathFinder
  • ViewLog/PRO

Salient Points

    • Dynamic loading & unloading of multiraster data.
    • On the fly projection settings.
    • Compatible with ArcView 3.2 and lower versions.
    • Feature rich and intuitive for all levels of GIS users. Basic GIS functionalities such as pan, zoom, identify, fast navigate and advanced functionalities such as combined spatial and data queries, template based to the scale printing, document management system have been incorporated.
    • Digitizing the features in ArcView and plotting the images.
    • Dynamic Linking/Viewing of the Borehole Log Images.
    • Training the users in GIS, GPS, ArcView
    • Engineering and GIS – Borehole Manager