To make the DEM I used the IDRISI routine RECLASS to convert the negative values to zero and then converted the elevation range in the ASTER DEM to the elevation range given by Ong Wee Seck in his Map Report cited above. The image of the island was then clear enough to use WINDOW to remove unwanted areas. I used RECLASS again to derive the classes shown in the map. The black areas were added using a graphic program, but I did not do any cosmetic work on the image.
The analyst should validate the DEM before using it and, if necessary revise the method used to derive it. For example, GDS does an absolute DEM as well as the relative DEM used here. The accuracy of the absolute DEM depends upon how well the analyst prepares the additional elevation and georeferencing data required by GDS.
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