King Faisal University

Water Studies Center


    Adel M. Elprince and Yousef Y. Al-Dakheel
    Water Studies Center, King Faisal University, Al-Hassa, Saudi Arabia

    • The locations of irrigation and drainage canals are, often, determined by visual estimations obtained from a base map for the project area. Occasionally, the water manager may need to use a map that contains little or no coordinate information. This is a problem if he intends to project this map with another in a multi-layer database. In this study we used the coordinates of selected ground control points (GCPs) obtained with a Trimble GPS unit to transform (register) the network base map (dated 1970; 1:10000-scale; unknown coordinate system) digitized in units of the base map into metric UTM system. Registration was done using affine transformation in ARC/INFO GIS. The accuracy of this procedure was analyzed by comparing the GPS positions of 40.72 km one-way-roads with their corresponding GIS transformed positions. A 45-m buffer was required for at least 95% of the GIS roads to occupy the same GPS road positions. The registered network map was successfully updated by overlaying a residential area map developed from recent SPOT image (1998) and a soil salinity map developed using variogram and kriging analysis with a scale of 1:45000 as an upper limit. Errors in the GPS measurements, digitizing, marking GCPs on the base map, and the transformation numerical method represented 4, 7, 22, and 67%, respectively, of the RMS error (22.5 m) introduced in the estimation of network positions.