International Archives of Photogrammetry and Remote Sensing, Vol. 32, Part 7-4-3 W6, Valladolid, Spain, 3-4 June, 1999 
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Fig. 5. Integration result with undulating terrain. Direct comparison with Fig. 4 shows the improvement on all scale levels. 
4.2 Accuracy Considerations 
To get an idea about the quantitative behaviour regarding the 
accuracy, we calculate accuracy measures for two examples. In 
example 1, we use measurements of two scales, i.e. a fine scale 
DTM with aim grid, which approximates the grid width of 
laser scanning DTMs, and a second one on a coarser scale with 
4 m grid width. The lower resolution measurements are more 
precise; thus the situation is similar to the examples presented in 
Figures 2 to 5. 
Example 1: DTM area of 256 by 256 m 2 
Grid width 
Measurement noise 
Fine scale DTM 
1 m 
0.35 m 
Coarse scale DTM 
4 m 
0.10 m 
Std. dev. 
Max height difference 
Integration result for 
the fine scale DTM 
0.28 m 
0.82 m 
Table 2. Accuracy results of integration of two DTMs. 
From this table it is easy to see that the higher accuracy of the 
coarse scale DTM contributes in improving the accuracy of the 
fine scale DTM. The overall error reduction is about 25 %. The 
maximum value of the height differences in all grid points on 
the fine scale calculated from the DTMs before and after 
integration is about 3 times the standard deviation. This means 
that there is a quite homogeneous improvement over the 
complete area covered by the DTM. 
In the second example, three DTMs which differ in resolution 
and accuracy are introduced into the integration approach. The 
fine scale DTM is fairly imprecise compared to both other 
DTMs. 
Example 2: DTM area of 1280 by 1280 m 2 
Grid width 
Measurement noise 
Fine scale DTM 
40 m 
0.70 m 
Medium scale DTM 
160 m 
0.10 m 
Coarse scale DTM 
320 m 
0.10 m 
Std. dev. 
Max height difference 
Integration result for 
- fine scale DTM 
0.61 m 
2.22 m 
- medium scale DTM 
0.10 m 
1.78 m 
Table 3. Integration of three DTMs. 
As in the example before, we observe an improvement of the 
accuracy of the fine scale DTM in this case of about 15 %. It is 
interesting to see what happens on the medium scale after 
integration of all three DTMs. Obviously, the accuracy is 
dominated by the medium scale DTM supported by the coarse 
scale DTM. The contribution from the fine scale DTM on the 
medium scale is probably negligible. This can be seen from the 
maximum height differences. The 2.22 m difference between 
the integrated DTM and the fine scale DTM shows up at the 
medium level again with an amount of 1.78 m. The reduction in 
size basically reflects the low-pass filter effect of the wavelet 
scaling function.