| Summary: | 碩士 === 國立臺灣大學 === 地理學研究所 === 85 === Grid DTM is the most popular structure in representing DTMs. Traditional topographic maps are informative and widely available thus make them an ideal source for creating grid DTMs. The data quality of resulted grid DTMs from contours is affected by factors including: interpolation method being used, quality of original contour map, and characteristics of terrain area. This paper investigates the effect of these factors by a series of tests using real terrain data. Two contour data sets are created from each of four 1/5000 topographic maps. These contours are interpolated using the four methods provided by ARC/INFO GRID modules: IDW, Kriging, Trend and Spline. The difference between these methods is significant. Result of tests shows that trend and spline are not suitable for interpolation terrain contours. The result of IDW and Kriging are close and better than that created from trend and spline methods. Accuracy of resulted DTMs decreases as resolution reduces, and the result is smothered. The maximum slope of the coverage with resolution of 40 meter is smaller than that of the coverage with a 10 meter resolution, and its standard deviation and mean are also smaller. The interval of contour is another factor influencing the accuracy of results. If more accurate results are needed, users should use contours with smaller interval. The characteristics of terrain is another critical factor. The accuracy of results will be higher for simple terrain area. Topogrid is another interpolation provided by ARC/INFO. In general, it performs better in area of complicated terrain.
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