ACCURACY ASSESSMENT OF CONTOUR INTERPOLATION FROM 1:50,000 TOPOGRAPHICAL MAPS AND SRTM DATA FOR 1:25,000 TOPOGRAPHICAL MAPPING

摘要

One major problem engendered by poverty in less-developed countries is that of inability of such countries to carry out fresh medium-scale topographical mapping at regular time intervals using expensive but accurate topographical mapping techniques. For such countries, an alternative which has proved to be cost-effective and efficient over the years is topographical map revision using existing topographical maps, satellite imageries and other free spatial data sources. However, extracting contours from existing topographical maps for inclusion in a new digital topographical map, often at a larger scale, is not usually a straight-forward process due to differences in map units and contour intervals between the existing base maps and the new map. Although free spatial data sources such as the Shuttle Radar Topographic Mission (SRTM) digital data provide excellent base data for extracting height data for topographic mapping, such data sets need to be adequately evaluated and subjected to further processing before extracting contours needed for topographical mapping. Extracting topographical data by contour interpolation from existing topographical maps and SRTM data therefore necessitates accuracy assessment of the interpolation result to ascertain its suitability for topographical mapping. This paper presents a framework for accuracy assessment of interpolating contours from 1:50,000 topographical maps and SRTM height data for topographical mapping at the scale of 1:25,000. Accuracy tests of contours interpolated from the two sources are performed for different terrain configurations and contexts to determine their suitability for topographical mapping in different scenarios. Using an on-going 1:25,000 topographical mapping project as a case study, the use of this contour interpolation accuracy assessment model for arriving at the best strategy for the mapping is also presented.