coordinate transformation tool for android platform ...

COORDINATE TRANSFORMATION TOOL FOR ANDROID PLATFORM CAPABLE OF REPLACING HANDHELD GPS RECEIVERS Chanaka Alahakoon, S. R. Kodituwakku, Jagath Gunathilake Postgraduate Institute of Science, University of Peradeniya, Sri Lanka Global Positioning System (GPS) is a United State owned system for providing position, navigation and timing services. Global Navigation Satellite System (GLONASS) is a Russian equivalent to GPS targeting same set of services. The basic idea behind these two systems is to build a constellation of satellites having the capability of transmitting one way signal to ground base receivers and help them derive the location and timing. Ground base GPS or GLONASS receivers can be varying from simple hand held mobile devices like smart phones, vehicle navigation systems, simple dedicated handheld receivers etc to more complicated high accuracy devices like deferential GPS receivers. The dedicated handheld GPS receivers are configurable to perform complex coordinate transformations and provide grid coordinates to suits specific regional needs where as smartphones works with limited coordinate systems available for them by default tools like Google maps. Thus smart phones are not suitable for accurate surveying work that needs specific coordinate systems for specific regions. With this backdrop, a software tool called CTDroid has been developed for Sri Lanka targeting android devices with inbuilt GPS receivers in order to come up with an inexpensive alternative to professional handheld GPS receivers. The development was carried out using Java. The tool is capable of accessing GPS and GLONASS sensor data from the device using Android Application Programming Interfaces (API’s) to perform datum transformation and projection using manually configurable parameters to come up with grid coordinates that suits Sri Lanka based on Kandawala datum. For the datum transformation, it uses the standard Molodensky datum transform algorithm while for the projection it utilizes Transverse Mercator Projection available with open source Proj4J projection library. Proj4J is a port of Proj4 C library originally developed by Gerald Evenden and then by USGS. Both these libraries are a part of the MetaCRS group of projects hosted by OSGeo. The proposed algorithm was tested against two popular tools: ArcGIS and Geotrans for same set of parameters and found out to be accurate up to 1 cm but the actual positional accuracy may depend on the device sensor itself. The software product having many other capabilities including coordinate transformation with forward and back projection, saving with the help of SQLite database, exporting using KML or GPX, navigating and sharing collected data together with capabilities for visualizing them on maps, was made available to Android community as a free tool via Google Play. The tool can be installed on any android device having OS version 2.3.3 and above. It can replace or supplement standard handheld GPS receivers and can reduce costs of spatial information gathering activities. Further improvements of the tool will include seven parameter Helmert transformations and hence will support more accurate SLD99 datum. Keywords: Android, GPS, Coordinate Transformation, Proj4J, SQLite FOSS Tools used : Proj4J, SQLite, Android, Java, Netbeans