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Web based Satellite Data Archival Information System (SDAIS) using Mapserver

B. Padmapriya
M.E. Geoinformatics , Institute of Remote Sensing,
Anna University, Chennai , India.

Dr. D. Thirumalaivasan
Assistant Professor, Institute of Remote Sensing,
Anna University, Chennai, India.



ABSTRACT
Data Warehouse of an institution or an organization has to store huge volume of satellite data, which are accumulated over a period of time. When someone wants to know whether data pertaining to a particular sensor is available for a given area of interest (i.e. study area, watershed boundary, administrative boundary etc.,),it requires enormous manual search. When the data accumulates over a period of time, manual search will be cumbersome and requires a database to maintain the data. In this context, a database, which is web-based and which can provide information based on the spatial query will prove to be an ideal choice.

Taking these features into account this study has been developed. The aim is to develop an information system (SDAIS) to facilitate managing satellite data in a Data Bank and implement this information system as internet/intranet application. The basic idea behind is to develop this information system using the open source software readily available in the Internet. In addition, an attempt is made in this study for providing additional functionalities than what is available with the open source GIS Map server i.e., development of spatial query for any polygon say an administrative boundary , watershed boundary,etc.

1 INTRODUCTION
Internet based geographic information system involves management of both spatial and non-spatial data (attribute data).GIS has come to be indispensable tool for analyzing and managing spatial data. The open source license guarantees the freedom to read, redistribute, modify and use the software freely (OSI). Conventionally, satellite data are produced from data recorded by satellite sensors and transmitted to Earth where computers process the data into images. These images are collected and stored in the Data Bank/Data WareHouse. The details such as Path-Row etc., are stored either in a ledger or in a database. However, when someone wants to know whether data pertaining to a particular sensor is available for the area of interest (i.e. study area, watershed boundary, administrative boundary etc.,), it requires enormous manual search. In order to overcome such shortcomings, a web based GIS solutions using map server has been used. The objective is to develop an information system (SDAIS) to facilitate managing satellite data in a Data Bank and implement this information system as internet/intranet application. The basic idea behind is to develop this information system using the open source software readily available in the internet. In addition, an attempt is made in this study for providing additional functionalities i.e., development of spatial query for any polygon say an administrative boundary, watershed boundary, etc. The application is designed using the spatial map server and the scripting language PHP. Database is created using MySQL.

2 END USER REQUIREMENTS
The application should satisfy the following user requirements.
  • User should be able to use the application from any browser
  • Large number of users should be able to use the application simultaneously.
  • The performance of the application should not degrade, with the increase in the number of satellite data available on the site.
  • User should be able to view a complete list of data available on the SDAIS site.
  • User should be able to search the satellite data list either by selecting their choice or by selecting their area of interest from the Path and Row (index) map.
Taking these requirements the following Open Source GIS and RDBMS Tools/Software are used in this study.

  • Client Side Scripting - HTML
  • GIS server - Map server.
  • Server-Side Scripting - PHP
  • Database server - MySQL

3 DESIGN METHODOLOGY
The design of the application has been split into different steps to enable easy development. This application would enable hosting of the website on a Microsoft Windows Platform or Linux Platform. The development of SDAIS involves steps such as Data collection, Database Design, Application design and Setting query.

3.1 Data Collection
This archival information system is developed for managing the spatial and non-spatial data from Data Bank, Institute of Remote Sensing, Anna University.

3.1.1 Spatial Data
  • The map contains all the district, taluk, and block boundaries of Tamil Nadu.
  • The index maps are collected from IRS Data Bank. It gives the Path and Row information of the satellite. The index maps of the following are collected.

              IRS 1A/1B - Sensor LISS I and LISS II scale 1: 6,000,000
              IRS 1C/1D - Senor LISS III ,PAN scale 1:6,000,000

  • Watershed boundary map is collected.

3.1.2 Non-Spatial Data
The satellite data availability in the Data Bank is collected. All the hardcopy and softcopy(CD-ROM) are collected. Data of IRS 1A,1B,1C LIII, 1C PAN, 1C MERGED,1D, LANDSAT_TM, LANDSAT_MSS and SPOT are available.

3.1.3 Data Organization
Spatial data was prepared for Administrative boundaries which includes districts, taluk and blocks, Watershed boundaries and index maps. Union between the administrative boundary and index map was done. The final data is in the form of shape files with extensions .dbf, .shx and .shp.

3.2 Software used

3.2.1 Mapserver
The University of Minnesota's Map server is an open - software for building web-enabled mapping applications. The core of the system is a Common Gateway Interface(CGI) application that allows developers to rapidly build and deploy web applications based on GIS databases. The software builds upon other popular open source or freeware systems or libraries like Shaplib, FreeType, Proj.4,GDAL/OGR for input and output data support. Mapserver will run where most commercial systems won't or can't on Linux/Apache platform. Mapserver is known to compile on most versions of Unix/Linux, Microsoft Windows and even MacOS.

The Mapserver system includes mapscript which allows popular scripting languages such as PHP, Perl, Python and soon even Java to access the mapserver C API. Mapscript provides a rich environment for developing applications that integrate disparate data.

Some of the features of Mapserver CGI are,
  • vector formats supported: ESRI shapefiles, PostGIS, ESRI ArcSDE and many others via OGR
  • raster formats supported: TIFF/GeoTIFF, EPPL7 and many others via GDAL
  • quadtree spatial indexing for shapefiles
  • fully customizable, template driven output
  • feature selection by item/value, point, area or another feature
  • TrueType font support
  • support for tiled raster and vector data
  • map element automation (scalebar, reference map, and legend)
  • scale dependent feature drawing and application execution
  • thematic map building using logical or regular expression based classes
  • feature labeling including label collision mediation
  • on-the-fly configuration via URLs
  • on-the-fly projection

3.2.2. Hyper Text Preprocessor(PHP)
PHP is a server- side embedded scripting language. This means that it works within a HTML document and confer to it the capacity of generating content on demand. PHP is simple, an almost natural way of using databases and platform independent and there are versions for various flavors of Windows, Unix and Linux and for a number of web servers including Apache and Internet Information Services. PHP works in a similar way to JSP and ASP: script sections are enclosed in tags and embedded with an HTML page. These scripts are executed on the server before the page is sent to the browser, so there is no issue of browser-support for PHP pages.

The advantages of PHP are as follows:
  • Simplicity.
  • Robustness of the language and scripting engine.
  • Connecting to ever increasing number of database servers
  • Shorter development cycles.
  • Ease of creating modular and reusable components.

3.2.3 MySQL
MySQL is a relational database management system. It is a small, compact, easy to use database server, ideal for small and medium sized applications. It is a client/server implementation that consists of a server daemon mysald and many different client programs. It is available on a variety of UNIX platforms, Windows NT, and windows 95/98. On UNIX platform it uses threading, which makes it a high performance and highly scalable database server.

Some of the features of MySQL includes
  • Speed, Robustness and Ease of Use
  • Programming language API's for clients to access the databases
  • Large Tables
  • Language Support
  • Cost Advantage

3.3 Database Design
Tables are created using MySQL. MySQL is a relational database management system, which means it stores data in separate tables rather than putting all the data in one big area. Separate tables are created for each satellite. All the tables are stored in a single database. The mysql utility sends the SQL commands to the MySQL server, and prints the result of the SQL command in the command line. The attributes of the table includes data type, Path and Row, Date of Pass, Sub scene, Scale. Connection between PHP and MySQL is established. Connection with the database is established such that the user would be able to select the spatial feature and query the associated non-spatial data maintained in the database.

3.4 Application Design

3.4.1 Simple Map Browsing
The application has been designed using spatial Map server and scripting language PHP(Hyper Text Preprocessor). The maps are presented in so that the user can perform the zooming operations (zoom in, zoom out, recenter) on the map. These operations allow the user to see the map at his/her own magnification scale. The Maps in this website are generated dynamically based on the geographic selection made by the user.

Customizations that are possible include the following:
  • Reference Map The reference map is useful to indicate at any point of time where the user is in the map.
  • Map size The size of the map can be changed dynamically. This helps the user to view the map under different resolutions.
  • Zooming Options

The zooming options include zoom in, zoom out and centering the map. These options allow the user to view the map under different magnification scales. 3.5 Setting Query
Web - based GIS users can use a web browser to navigate maps and do some basic spatial query. The client sends a request to the server. The request from the client will be sent to the server by the way of HTML form. The server passes the request to the GIS server. After some processing the request is returned back as response to the client. The application is split into the following parts:

3.5.1 Non - Spatial Query
The non-spatial query generally consists of query form where the user can select their parameters of interest such as Data_type, Scale, Date of Pass, District, Taluk etc. Finally when the form is submitted (query presented by the user), the result contains only those features that matches the criteria are displayed dynamically. The search is based on District and Taluk.

3.5.2 Spatial Query
Two separate query, one based on the Administrative Boundary and other based on the Watershed are done.

· Administrative Boundaries
The user can select the level of query i.e. District level, Taluk level or Block level as shown in Figure 1.



Figure 1 Main Page Containing the Map file


Once the user queries on the map, the details about the selected area (district, taluk, block and path_row) are obtained depending on the level of query as shown in Figure 2. This is done by establishing a connection with the attribute tables of the themes.



Figure 2 Results of query


Further a query for database has been developed. It is similar to the non-spatial query. The difference here is, search is based on Path & Row. The Figure 3 shows the database query.



Figure 3 Querying the Database


Once the user submits the form, results are displayed in a tabular form shown in Figure 4 A link to home page is also created. Help is also available for the user to easy navigation. A printout of the results can be obtained.



Figure 4 Results of Querying the database


· Watershed Boundaries
Similar to the Administrative boundaries, the watershed map can be queried. The results will have the name of watershed , watershed code and Path&Row. Further the database can be queried.

4 DISCUSSIONS
Satellite Data Archival Information System(SDAIS) reflects the server side architecture, which has its own merits and demerits. The objectives proposed in this study are realized through the development of SDAIS. The results of the implementation shows the advantages and disadvantages of using SDAIS. These are summarized below.

Advantages
  • Easy development, deployment and maintenance.
  • Adherence to internet standards
  • Platform independent
  • No downloading of data required.
  • Overall performance is high.
  • User requires only a standard browser.
  • View modifying commands (zoom , pan) can be done by the client and the views are dynamically generated.
  • Search and Querying can also be done by the user.
  • Requires no additional software.

5 CONCLUSION
Satellite Data Archival Information System has been developed using the open source software. This work will be very useful for any organization working with satellite data. The fact that client can get the information at his/her own work place and all that is required is only a browser is the major advantage of this Archival Information System. This tries to leverage the power of GIS open source tools client. It can be extended to any geographical extent and made more flexible to talk to any heterogeneous platform.

6 REFERENCES
  1. Jesus Castagnetto, Chris Scollo, Sascha Schumann, Harish Rawat, Deepak Veliath (1999), 'Professional PHP Programming', Wrox Press Ltd, U.K, ISBN: 1-861002-96-3, Chapter 12, pp 288-303.
  2. Rasmus Lerdorf & Kevin Tatroe (2002), 'Programming PHP', O'Reilly & Associates,Inc, U.S.A, ISBN: 81-7366-311-4.
  3. Jay Greenspan and Brad Bulger (2001), 'MySQL /PHP Database Applications', M&T Books, U.S.A, ISBN: 0-7645-3537-4.

URL
  • Mapserver source code - University of Minnesota
           www.mapserver.gis.umn.edu
    • PHP script
          www.php.net MySQL
          www.mysql.com
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