— 
  
NS 
= | IN 
E E 
    
= 
C=C CN 
rows of points to be disrupted. 
The aim of this method is to get as good results as by man- 
ual editing easily with the help of a computer. Therefore the 
quality of the results is mainly concerned, on the other hand 
each process of calculation has not been explained in detail. It 
will become important to get theoretical bases about this 
method for solving problems in above. 
4. APPLY TO DEM RASTER DATA GENERATION 
A Digital Elevation Model is a series of elevation data usu- 
ally measured on a grid system. In the process of Local D'TM 
   
local DTM 
Xi 
(Xi, Yi, Z) 
editing, the accurate elevation at the concerned point is calcu- 
lated. Instead of selecting the point from the contour polyline 
nodes, local DTM calculation is applied at the each intersection 
of the aimed grid, then elevation raster data of the grid area will 
be created(Fig 7). Many methods have been studied to create 
DEM raster data from contour polyline data, however, generally 
those methods interpolate elevation value from only a few con- 
tour line nodes. As a merit of Local DTM method, the elevation 
value is calculated concerning general terrain shape around the 
point, so it's unlikely the whole data includes abnormal or ir- 
regular height points. Actually, examinations got pretty fine 
DEM data by this method. 
     
  
Fig 7 DEM raster data generation by Local DTM 
method 
References from Journals: 
Thapa, K., 1988, Automatic line generalization using zero- 
crossings. Photogrammetric Engineering and Remote Sensing 
vol.54;, No.4, pp.511-517. 
Dettori, G. and Falcidieno, B., 1982, An Algorithm for Select- 
ing Main Points on a Line. Computers & Geosciences vol.8, 
No.1, pp.3-10. 
References from Books: 
Yaguchi, A., 1983. Gendai Sokuryo-gaku 5. Nihon 
Sokuryokyokai, Tokyo, pp. 99-163. 
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