Methodologies
We approached development of a web based Land Information System (LIS) through the construction of a 3-tier web service architecture, comprising a client, middleware and server. Freely available, open, interoperable specifications, standards and technologies have been implemented as widely as possible at each level of this architecture. This research mainly focused on the construction of middleware providing the bridge between client and server tiers to support raster and vector geospatial data request, retrieval, integration and presentation. The methodology of this research can be broken down into three stages corresponding to the 3-tier web service architecture previously described.
- Server – In order to serve raster and vector geospatial data from multiple sources via the web we have implemented the OGC WMS and WFS specifications. Basically WMS and WFS enable users to request the geospatial data and retrieve the results in various formats. WMS produces the requested geospatial data in a variety of raster formats (e.g. GIF, JPG, PNG), whilst WFS produces vector data, typically, in GML. Due to the resulting data type returned from the server, WMS is sometimes called an image server, and WFS is called a GML server. This research has im3plemented an example of both specifications to deliver geospatial data as requested. We utilised the Minnesota map server [4] for the image server. This map server provided the mechanism to create and render image maps from Shapefile data (ESRI data format). We also developed the GML server in order to provide the vector data in the form of GML.
- Middleware – The middleware enables the application to retrieve the geospatial data from different servers. It utilised Java servlet [7] supporting CGI. This servlet enables the server to communicate with the client via the URL. There are four main functions that the servlet middleware performs:
- getting the user request;
- connecting and retrieving data from map servers;
- combining the requested data;
- delivering the resultant data back to the client application.
- Client – A client map viewer has been developed to render the data requested by the servlet. This application typically provides several common GIS functions e.g. pan/zoom, querying and rendering. This application was developed using Java technology. The applet is an application that is able to run on a web browser.
Additionally a relational database (RDB) was used to create an ad hoc database in order to integrate data into a single source to ease data management. The RDB structure to store the geospatial data has been adopted and adapted from [1] (Figure 4). This type of RDB is often referred to as a Spatial Relational Database (SRDB).
Implementations
Data Preparation
For this research a test area was chosen covering commercial, industrial, forested and residential portions in the Mukim of Damansara, one of the province-like administrative regions of the state of FTKL. As mentioned previously, three types of JUPEM datasets relating to spatial data of land administration and geographic map features were selected wrapping the tested area i.e. land parcel data, topographic map data and aerial images.
Initially, five high resolution aerial photographs acquired from Aerial Photography Section were rectified using ground control point (GCP) from digital topographic features. After given a spatial reference, the five photographs were mosaicked producing a larger image of the test area. ERDAS IMAGINE software was utilised for these tasks. It was then gridded into small bounding rectangles covering the relevant area for the implementation of the application. During the process it has to be transformed from raster TIFF file to ERDAS IMAGINE (.img) format and finally to JPEG format file to achieve a lower resolution and compact file size image in order to distribute on the web.