Improved geodetic control by GPS for establishing a Geographic Information System for Sri Lanka
Sri Lanka is in the process of establishing a Geographic Information system (GIS). Map layers such as land use, elevation, soil type, transportation and cadastral layer showing property boundaries have to be included in the GIS. Of these many layers, the cadastral map layer requires the highest level of spatial accuracy because it is expected to resolve problems in land transaction, land registration and boundary disputes in the country;This dissertation identifies the procedure of establishing a GIS for Sri Lanka and recommends solutions for the ensuing problems. Specifically, it investigates the accuracy of the existing geodetic control network, which is the accurate linkage mechanism of the GIS, develops a procedure for establishing a new Global Positioning System (GPS) geodetic network to satisfy the needs of the GIS, develops a suitable procedure for the transformation between old and new coordinates in the country and recommends a cost-effective and fast methodology to get cadastral level spatial information to the GIS;Present geodetic control was analyzed and found that it provides only one part in 30,000 spatial accuracy, but one part in one million is desired for 25 km apart primary control points. Working with simulated GPS data obtained by introducing random and systematic errors to adjusted distances of the geodetic network, a GPS observation procedure was developed to establish a new geodetic control network;When a new geodetic adjustment is performed, transformation parameters are necessary to transform coordinates between old and new systems. Working with a set of newly adjusted coordinates and old coordinates, obtainable accuracy of the coordinate transformation of the country was analyzed on a provincial and district basis. A software "Con-cord" was developed to do many types of coordinate transformations in the country;To get cadastral data into the GIS, the accuracy of scanning and vectorization procedure was found to be comparable with manual digitizing, for cadastral maps. For the elimination of digitization and mapping errors, a least squares sequential adjustment procedure was developed using additional linear, angular and area measurements, upgrading digitized property corners.