GPS enabled mobile GIS services


Client-Server Communication
Many options were studied for two-way data transfer, out of which five probable solutions are described. Considering the nature of applications, CORDECT technology will be used as an access mechanism. Few salient points of different technologies are as follows

Using VHF Radio
Mobile system can be connected to GIS server by two-way VHF Radio within a range of 25 Kms. Simultaneous voice and data transmission rate up to 9.6 Kbps is possible. Such a system, working with VSAT backbone is commercially available from Motorola. Ref. NGO(MSSRF) at Pondicherry.

IS-95 CDMA
Code Division Multiple Access known as CDMA is emerging technology in India. BSNL has selected this technology to provide Internet access to rural areas. VSAT backbone range can be extended by further 20 Kms and data rate up to 14.4 Kbps can be achieved without modem. Mobility is limited within defined cell.

Wireless Application Protocol over GSM Network
The WAP is currently de-facto industry standard for Internet access for wireless devices. Existing GSM network of cellular provider along with WAP Gateway and WAP phone can be used for GIS database connectivity. Due to limited bandwidth, screen size and memory of mobile device, GIS data must be re-structured in WML card and deck format. User interaction is provided with set of cards and data is transferred in form of deck. Maximum size of compiled byte code per deck is limited (1400).

GSM Network
GSM network is widely utilized for voice communication because, the data port is not supported. PDA with GSM modem attachment can be connected to GIS server but without protocol support for vector data through put can not be optimum. GIS plug-in (ESRI ArcPad) at client side and ArcIMS at server side can solve the problem as client-server data transfer takes place as a XML string. The solution will work where cellular network is existing.

Wireless Digital Enhanced Cordless System (CORDECT)
CORDECT technology provides data access from remote mobile platform up to radial distance of 10-35 Kms. Works well with VAST and provides up to 70 kbps data rate through voice port as well as data port without modem. System can be configured for 12 channel/32 kbps or for 6 channel/70 kbps. Compatible mobile instrument is cheap (Rs. 13500).

Results
Comparision of accuracy of mobile system with post proccesing technique is shown in Table 1

Conclusions
Based on literature survey and planned applications, the probable H/W and S/W solutions can be
  • Proprietary H/W from GPS vendors like Sokkia (iMap), Leica (GS-50), Trimble with added limited GIS capability.
  • Proprietary S/W from GIS vendors like ESRI (ArcPad), Autodesk (Onsite), MapFrame (Field-Smart) with third party PCMCIA type II GPS receiver and industry standard Palm Top
For our requirements, we are proposing prototype design for two systems based on above second option. One system will be based on Compaq iPAQ Palm Top , Teletype PCMCIA GPS receiver and ESRI ArcPad GIS S/W. The second system will be based on SIMPUTER with Linux operating system, GIS components like Map Object /MAPX/Geo-concept kit and PCMCIA type GPS receiver

Technological developments have provided tools to design such a mobile GIS system but still there are certain limitations w.r.t. data transmission rate, processing power, resolution of display and no JDBC type of support for GIS applications. These limitations must be kept in mind while designing an application.

Acknowledgement
We are thankful to Shri A. R. Dasgupta, Deputy Director, SITAA for providing us an opportunity to explore utility of handheld GPS, Palm Top computing and lightweight GIS for the purpose of designing a mobile GIS system.

References
  • Udani, P. M., 2001, Issues regarding integration of GPS data with GIS database - Map India 2001
  • Dr. Venkatachary, 2000, Remote Sensing Applications for Natural Disaster Management, Workshop proceeding on Space Technology for Rural Development- NGOs perspective.
  • Roy, P.S. , et. al. 2000, Natural Disasters and Their Mitigation , RS and GIS perspective, IIRS Publication
  • David Maguire, 2001, Mobile Geographic Services –Map India 2001
  • Rao, Mukund, 2000, A Framework for Establishing a Disaster Management System- ISG News Letter
  • Narayanan, Sampath, 2001, GIS in Midas Installations – CorDECT WLL Technology , Map India 2001
  • Purohit, Shirish, 2001, Wireless in Local Loop, Voice & Data, January 2001
  • Dey, Lipika et. al. ,2001, Bringing Internet Services to Wireless Devices, IETE Technical Review, July-2001
  • GPS World, September 2001, Product Survey on Handheld Devices
  • GIM International , July 2000, Product Survey on In-field Mapping System
  • Wilson, J. D., 2001, Mobile GIS- The Next Frontier, GEO-World , June 2001
  • Massoud, Sharif, 2000, Integrated Application of Geo-Techniques for Database Updating Studies, ISPRS 2000
  • Udani, P.M., 2000, Measurement accuracy of GPS data- Technical Note
  • Dr. Srivastava P.K., Trivedi S. P., Rana Y.P. , Udani P. M. et. al. 2001, Base Map Generation Using IRS Stereo Data – Technical Note

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