Introduction of data packing methods for computerized digital terrain map production

Abstract

The computerized production of digital terrain maps (DTM) was innovated through economizing in the data storage area. The innovation resulted in saving computation time as well. The bit plane method which is indispensable for saving working area, especially in the production of wide-range DTMs, and the method of compactly packing plural data into one word (PDOM) are introduced here. To assess the advantage of the PDOM over the conventional sequential data storage method (SDSM), a comparison of them was made in terms of computation time. In either case, the altitude interpolation was made in two different ways, that is, by proportional allotment and by second-order polynomial equation. DTMs were produced for two different model areas, one with a scale of 1/1, 000 and the other with 1/5, 000. It turned out that the DTM production efficiency depends largely on the data storage methods (PDOM and SDSM), but not on the altitude interpolation methods. The computation time with PDOM was only 1/4 for the 1/1, 000 and 2/3 for the 1/5, 000 of that required with SDSM. Thus the larger the average number of co-ordinate data per contour line, the shorter is the production time of a DTM with the PDOM which is shorten also than with the SDSM.