The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
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Figure 7. Grid (left) and mesh-divided features (right) 
O Intersection point ( Feature line 
• Sampling point □ Feature polygon 
Figure 8. Grid DEM integrated features 
As figure 8 shows, there are 3 different features, points, lines 
and polygon, which are integrated to the grid mesh. They are all 
divided up by the grid cells, and the intersection points are 
marked up in the figure and recorded. 
3.2.2 File structure: 
The new structure of DEM include two parts: one is grid file, 
which is the existing grid DEM file, but the elevation of any 
grid cell that contains terrain features is replaced by a pointer. 
The other one is the terrain feature file which records the 
feature points, lines or polygons of the relevant DEM. The two 
parts was associated with the pointer which is recorded in grid 
file. • 
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Figure 9. New file structure 
• Feature file: All the feature information and the 
intersection points of features and grid mesh in a grid cell 
are stored as an item (in one row) in the feature file. The 
features are stored by a series ordered points in the file, 
feature codes are used to distinguish different feature 
types. So the feature information is stored as figure 10. 
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pi 
FN1 II FC1 
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P2 11 FN2 
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1 PN2 II XI 1 
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Figure 10. Feature file structure (here PI, P2... represent the 
pointer; FN1, FN2...represent the number of feature types in a 
grid mesh; FC1, FC2...represent the feature code; and PN1, 
PN2...are the number of points in a grid mesh; while at last, XI, 
Yl, Z1 ...are the coordinates of the points.) 
Comparing the two methods, the new grid structure is a little 
difference from the existing one, it retains the original structure 
integrally and only replaces some cell values by a pointer. And 
the feature structure gives a detailed description of the DEM 
features. The pointers associate the two parts, so this new 
structure is not only compatible with existing grid DEM, but 
also integrates the terrain features. 
4. VISUAL TEST AND EXPERIMENT 
4.1 Experiment of the correction method 
• Grid file: The structure is almost the same as the above 
structure in 4.1, the only difference is that the elevation 
data of the grid cell that contains terrain features is 
replaced by a pointer. And the pointer locates to the place 
where terrain features are stored and collected relatively 
precisely in the feature file. Then the two parts was 
associated. (Figure 9) 
Using the above new data structure of DEM, experiments are 
made to test the effect of integrating terrain features in grid cell,