P. M. Udani
R. K. Goel
Informatics Applications Division
Space Applications Center, SAC, P. O. Jodhpur Tekra, Ahemdabad
Many emerging applications of GIS involves integration of lightweight hardware like Palm Top PC, positioning system like GPS and wireless communication tools based on GSM or future WLL and GPRS for real time data capture and field verification. As of today, there is no such integrated system available in INDIAN market. At Space Applications Center, we have proposed to explore utility of such mobile GIS platform for various prospective applications. H/W and S/W requirements, existing communications backbone in urban areas and future planned network for rural areas is critically studied. These requirements are to be converted in form of a prototype design for GPS enabled mobile GIS services using Palm Top with GPS card and wireless modem/GSM PC card phone for information exchange and remote updating of database at server side for real time decision making.
System design goals are to provide customise forms and front end interface for field data collection and verification, data viewing, what lies/where lies type of location query and handy decision making tool during disaster relief, rehabilitation and rescue operations. Due to limitations of communication backbone transition between server and client must be bare minimum. Therefore applications must be planned considering capability of lightweight GIS tools and possible customisation at client side. GUI based applications S/W will meet requirements of users in the following areas
- Real time data collection for dynamic applications related to disaster.
- Mapping of infrastructure facilities like school, post office, health center, bank, veterinary dispensary, bus stop, police station , electric power pole etc
- Visualisation of villages and population affected based on flood condition
- Visualisation of relief and rehabilitation centers and routes for approach
- Position of drinking water sources and its service zone
- Handy tool for health worker who has to move door to door for data collection
- Mapping of forest boundary, area affected by forest fire, area under energy plantation
- Military field work
- Provide information in tabular form regarding agencies and individual with their resources and responsibilities for the purpose of the disaster management
- Road network mapping within village and connectivity to relief center
- User friendly forms for socio-economic data collection for GIS databases
To meet above requirements, it is proposed to design two systems. One system will be based on Compaq iPAQ pocket PC with 12-channel GPS receiver and GSM modem for wireless connectivity. The micro browser provided with iPAQ has no functionality to handle GIS data. This limitation can be rectified by lightweight GIS plug-in like ArcPad from ESRI. ArcPad is selected because of its specific features like ArcIMS compatibility, hyperlink facility for different attachments and support for MrSID format, which is essential for wireless device. ArcPad plug-in and IMS combination is one time investment to avoid repeated and prolong wireless connectivity with server. Second system will be designed using Simputer with Linux Operating System with compatible embedded GIS components. Server connectivity will be provided by exploring WLL/GSM and VSAT combination.
Most of the listed applications are related to taking advantage of mobile GIS platform during field operations. To show case this capability database related to taluk boundaries, village boundaries, settlement positions, transport network, Socio-Economic data, amenities data, relief center with resources, control center with assigned responsibility and associated work force details drawn from different department are required as part of digital database. Spatial data related to jurisdiction of police, home guards, fire brigade, electricity board and NGO etc. with appropriate attribute will be linked to core database.
Depending upon requirement, GPS field observations for point features, registration/rectification of satellite images as well as cadastral maps are also required. Experiments are conducted using survey quality GPS receiver and navigation type handheld receiver. The experience acquired in improving coordinates accuracy will be used for enhancing database accuracy. After removal of Selective Availability (S/A), single point positioning accuracy of the order of 10 meters is obtained. (Ref. GPS WORLD APRIL 2001). Accuracy figures are given under results caption. For targeted applications, correct attribute information is more important then location accuracy. Broad structure/procedure to be followed during database collection using GPS-GIS integrated platform and data transfer between client-server is given below
- Survey planning: GPS satellites are available for all 24 hours and observation can be taken at any place at any time. For better accuracy planning is required for best GDOP value and appropriate observation window.
- Logistic support: Proposed prototype system will support simultaneous display of raster and vector data. Therefore, IRS Satellite merged/ortho product with highlighted feature will be kept in background as a guiding tool.
- System set up: Wireless connectivity of GPS receiver with serial port or infrared port will be available. Through customised form of lightweight GIS tool (ArcPad), the communication port can be configured to receive NMEA formatted GPS data in terms of latitude, longitude and Geoid height (GGA format) or Easting, Northing and Ellipsoidal height (LLK format) with datum/projection specification. GPS-GIS interface will be configured for direct coordinate correction of point feature or insertion of new feature in to GIS database. After appropriate attribute entry, data will be prepared for up-loading at server site.
|Site No.|| Mss
|Sr 9400 Gps Coordinates|| Processed
|1 starting||Lat 22 42 29.61
Lon 72 49 29.54
|Lat 22 42 29.72
Lon 72 49 29.65
|Lat 22 42 29.74
Lon 72 49 29.57
|1 ending||Lat 22 42 29.69
Lon 72 49 29.49
|Lat 22 42 29.77
Lon 72 49 29.70
|2 starting||Lat 22 34 45.06
Lon 72 58 12.73
|Lat 22 34 45.01
Lon 72 58 12.67
|Lat 22 34 44.99
Lon 72 58 12.73
|2 ending||Lat 22 34 44.83
Lon 72 58 12.61
|Lat 22 34 45.07
Lon 72 58 12.53
|3 starting||Lat 21 42 53.08
Lon 73 02 48.08
|Lat 21 42 51.89
Lon 73 02 48.34
|Lat 21 42 51.65
Lon 73 02 48.55
|3 ending||Lat 21 42 52.23
Lon 73 02 48.34
|Lat 21 42 51.86
Lon 73 02 48.32
|4 starting||Lat 21 16 10.43
Lon 72 57 27.88
|Lat 21 16 10.35
Lon 72 57 27.87
|Lat 21 16 10.55
Lon 72 57 27.79
|4 ending||Lat 21 16 10.41
Lon 72 57 29.97
|Lat 21 16 10.35
Lon 72 57 29.91
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.
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 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).
Comparision of accuracy of mobile system with post proccesing technique is shown in Table 1
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.
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.
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