Digital Cambodia Web GIS

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					                         GISWEB SERVER FOR DATA SHARING

                                         KYAW Sann Oo
                 GIS Application Center, Asian Institute of Technology, PO Box 4,
                           Klong Luang, Pathumthani, Thailand. 12120

                                       Lal SAMARAKOON
              Earth Observation Research Center, Japan Aerospace Exploration Agency,
        Triton Square Office Tower-X 23F, 1-8-10 Harumi, Chuo-ku, Tokyo,JAPAN 104-6023

KEY WORDS: WEBGIS, Greater Mekong Sub-region, Remote Sensing, Geographic
Information System


WEBGIS is the latest advances in GIS technologies that bring spatial information via Internet.
Access to spatial data over the Internet is growing rapidly and Information sharing through
GISWEB Server is important as it reduces cost of data, provide standard data, conformity of
data and data interoperability.
WEBGIS Server architecture development includes three main parts. They are hardware
architecture, software architecture and data warehouse. Hardware architecture is a design based
on enabling high availability, accelerating performance, reducing costs and improving data
management. Software architecture is an ArcIMS based multi-tier architecture for better
performance and data distribution transparencies. The last one, data warehouse, is a design for
data sharing, data integration, and data interoperability.

This study attempt was made to demonstrate the potential of WEGIS using Cambodia as a Test
Area. Here National GIS inventory and JERS-OPS data were incorporate in WEB Server to
show the potential of WEBGIS.

The benefits of this study are regional RS/GIS information networking and capacity building,
information sharing and reducing poverty through sustainable development in GMS.


Availability of spatial data in digital forms integrated to a database refers to as Geographic
Information System (GIS) that provides widespread of interdisciplinary applications. GIS can
be recognized as 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. With the advancement of computer
technologies and telecommunication it allows for the emerging of GIS to be considered as a
distributed resource warehouses against the single user or networked within a local area. The
originally centralized mainframe GIS systems has been evolved along with the technology
development to a personal desktop of GIS, and to currently Distributed GIS services, which
include the applications of wired Internet GIS and wireless mobile GIS. The latest advances in
GIS have come most notably in the forum of the Internet. Access to spatial data over the Internet
is growing rapidly. Web-based GIS could provide interactive mapping and spatial analysis
capabilities reducing the problem of data ownership as data providers could open their sources
for online mapping and analysis.
The overall goal of this work is to demonstrate the potential of Internet for overcoming spatial
data access problems and for facilitating information sharing by large number of users
distributed all over the world. In presenting capabilities of Internet GIS, this work was carried
out to develop spatial database for Cambodia, one of the most important countries in the
Mekong Sub Region where data sharing plays a very crucial part. There is tremendous work
being carried out in the region by various national and international agencies creating various
information pertaining to land and water where most of them need to be addressed on spatial
domain. Further investment on these data generation need to be minimized by sharing
information and avoiding duplications. In this aspect, sharing possibility via Internet and
analysis over Internet is going to be very productive and advantageous for the sub region as well
as others involved in development projects in the region.

In this demonstration, the web GIS capacity was built using ArcIMS 3.1 software packages and
the sharing potential was exhibited using archived JERS-1 data and GIS information of
Cambodia. Authors would like to acknowledge the data provided by Japan Aerospace
Exploration Agency for this work.


Developing a Web GIS is more than simply buying the appropriate hardware and software.
Several strategies have been proposed to provide successful implementation (Alesheikh &
Helali 2001). The implementation strategies have been scientifically assessed and modified so
that the requirement of this case study can be met with minimum cost and time. Figure 1 shows
the Web GIS development cycle, which is described 7 major activities starting with the
requirement analysis and ending with on-going uses and maintenance of the Web GIS system.
To implement a successful GIS Internet application, several questions need to be answered
before design and implementation starts. The questions listed below give a good basis for the
type of information that is helpful to compile in creating a GIS web site:

Who will use the system? What level of expertise will users have with technology? With the
data? Is it an Internet of Intranet application? What data is required? Where will you acquire the
data and in what format? What type of hardware/network? Who will support the system? What
tasks will the application need to perform?

Designing the application for the Internet environment involves two main activities; authoring
Mapservices and designing the web site.

           Components                               Workflows
              Process                          Initiation
              Technology                       Implementation
            Organization                       Testing
                                               Project Management

                        Figure 1: Development framework and methodology
 This system consists of three district components: a server application, a client interface, and a
 data repository. It is conformed to a multi-tiered layered architecture typical of server-side
 Internet application (figure 2).

   Web Browsers                                                     WIN       RS


                                                            LINUX                         Other



             Client interface                        Server Application            Data warehouse

                                Figure 2: multi-tiered layered Architecture

 2.1 Hardware Architecture

 There are several hardware configurations that can support this system design. The
 configurations are: single computer configuration, two-computer configuration, and multiple
 computer configurations. In the single computer configuration, the Web server, application
 server, and database server are installed on a single computer. In a two computer configuration,
 the Web server is installed on one machine, and the application server and database server are
 installed on a separate machine. In the multiple computers configuration, each component is
 installed on a separate computer. The ideal configuration for a particular deployment depends on
 the anticipated number of users visiting the site each day, and the number of maps served. ESRI
 make the following recommendations based on the number of anticipated daily users.

                         Configuration        Anticipated Number of Users
                         Single computer      100 - 1000
                         Two computer         1,000 - 1,500
                         Multiple computer    1,500 +
                              Table 1: The number of anticipated daily users

 2.2 Software Architecture

 In this system it has multi-tiered architecture consisting of the presentation tier (Browsers and
 Clients), Business logic tier (Web server, Java connector, application server and spatial server),
 and data tier (supported data format).

 When the Web Server receives a request, it passes to Java Connector. The output from the
 connector is a request written in ArcXML. Once in ArcXML, the request is handed to the
 Application Server. The Application Server handles load distribution and keeps track of which
services are running on which Spatial Servers. When a request is received, the Application
Server hands the request to the Spatial Server running the services.

The workhorse of this architecture is the Spatial Server. The Spatial Server is made up of seven
server types: Image, Feature, Query, Geocode, Extract, Metadata, and ArcMap Servers. Four
service types access these servers: Image, ArcMap Image, Feature, and Metadata Services.
Spatial Servers are not accessed directly but rather through Virtual Servers. A Virtual Server is a
tool for managing multiple Spatial Servers. An incoming request is assigned to one of the
instances within the Virtual Server group running the service.

Architecture based on HTML viewer (figure 3). The HTML Viewer is written using HTML,
DHTML, and JavaScript. In this environment only one Image or ArcMap Image Service can be
displayed at a time.

All requests are generated using JavaScript, and all responses are parsed using JavaScript. To
handle the communications for requests and responses, the client browser must be Internet
Explorer or Netscape version 4.x or higher.

The architecture has been developed specifically for Internet applications. It is designed to
handle small Intranet sites as well as the industrial-scale needs of enterprise-wide systems or e-
business sites. It can scale to meet server capacity needs as Web site demand increases.
Additional Spatial Servers can be added quickly to existing Virtual Servers. It is also designed
to be flexible enough to work easily with other Internet tools and applications that need a
mapping component.

                            Figure 3: The HTML viewer architecture

2.3 Data Warehouse Design

The Japanese Earth Resources Satellite-1 (JERS-1)’s Optical System (OPS) is composed of
Very Near Infrared Radiometer (VNIR) and Short Wave Infrared Radiometer (SWIR). OPS
sensor has 8 observable spectral bands from visible to short wave infrared with 75 km x 75 km
extent (figure 4a).

In this case study, we used VNIR sensor’s bands with Geotiff format. The pixel size is
dimensioned to 18 x 18 meters. Sample image is subset into 525-tile grids. Tile grid size is 1390
x 1390 pixels approximately 25x25 kilometer (figure 4b). Study area covers entire country of
Cambodia. The main idea for resizing the image is to download faster than full image. Resizing
was done considering the band with availability in the region.

                                         75 km
                                                                        25 km
                                         Bands            75 km    km

                                    (a)                                       (b)
                              Figure 4: (a) full image; and (b) downloadable image size


GISWEB Server enables users to easily select, download, and deliver uploaded data and analyze
geospatial data. Operating under Windows, the interface for the translation operates through the
HTML viewer, giving GISWEB Server users a familiar, easy-to-use front end for translation and
download of published data. When creating a Web site using the HTML Viewer through
ArcIMS Designer, a hierarchy of directories and files is created. The Web site directory contains
a set of HTML files and a parameters file, along with two subdirectories; javascript and images.

The javascript subdirectory contains files that make up the HTML Viewer JavaScript Library.
These JavaScript files contain the functions that perform many of the common operations for the
HTML Viewer. The images subdirectory contains the graphic images used in the viewer pages
such as the buttons, icons, and logos. The HTML Viewer uses a library of JavaScript functions
found in several files located in the javascript subdirectory. These files are grouped into
categories based on viewer functionality—Basic Map, Custom, Extended Map, Interactive Map,
Legend, Print, Geocode, Identify/HyperLink, Graphic Selection, Query/Find/Search, and Buffer.
The categories, files, and hierarchy of dependency are illustrated below (figure 5(a)).

                         Basic Map

    Custom             Extended Map              Legend

                       Interactive Map            Print

         Identify/Hyperlink          Geocode

         Graphic Selection

        Query Find / Search


      Figure 5: (a ) Organization of the HTML viewer and (b) HTML viewer frame layout

The diagram above (figure 5(b)) shows layout for the Internet Explorer HTML Viewer. Each
area shows the name of the frame, the name of the HTML file that fills it, and its size in pixels.
The diagram is not to scale but provides a guideline for planning the layout for a new custom

The success of the technology is often determined by the usefulness of the applications it
provides. The following applications have proven that mapping and GIS technology are integral
part of information distribution over the Internet.
    1) Public information distribution
    2) Data sharing and
    3) Data integration

In order to satisfy above criteria, there were a series of main geospatial accessing tools that are
included in this system. They are zoom in, zoom out, full extent, active layer extent, zoom the
last extent, pan, pan to north, pan to south, pan to east, pan to west, download / hotlink, identify,
query attribute, find, measure, set units, buffer, select by rectangle, select by line/polygon, clear
selection and print function. Some powerful functions are show as below:
Zoom to Full Extent: Zooms to the full extent of the map.
Zoom to Active Layer: Zooms to the full extent of the active layer.
Zoom In: Zooms in on the position clicked on or the box dragged on the map.
Zoom Out: Zooms out on the position clicked on or the box dragged on the map.
Previous Extent: Zooms to the last previous extent. Inactive until user changes extents.
Next Extent: Zooms forward from the previous extent.
Pan: Pans the map as the user drags the pointer across the map.
Pan One Direction: Pans the map in one direction.
Identify: Displays a list of attributes for a selected feature.
Measure: Measures distances on the map.
Set Units: Sets the units for the Measure tool.
Query Builder: Constructs queries on MapService data.
Buffer: Inserts a buffer zone around a feature.
Attributes: Displays attribute information for selected features.
Clear All Selection: Unselects the current selection.

Future direction for this study will apply Open Source software. Which will reduce all licensing
costs of commercial software and it allowed modifying to source code of software.


[JAXA] Japan Aerospace Exploration Agency
[Restec] Remote Sensing Technology Center of Japan
[ArcIMS] ESRI Internet Map Server
[Tomcat] The Apache Jakarta Project
[OGC] Open GIS Consortium
[W3C] The World Wide Web Consortium
[J2SE] Java 2 SDK, Standard Edition, v 1.3.1_02
Alesheikh AA, Niaraki AS, Varshosaz M, Helali H Satellite Location & Navigation of Vehicles
on the International Transport Corridor of Iran, Russia and India. ISPRS papers, Dept. of
Goedesy & Geomatics Eng. K.N. Toosi University of Technology, Vali_Asr St., Tehran, Iran