In: Wagner W., Székely, B. (eds.); ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
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The frequency distribution of DZ values between evaluated 
models and reference models is shown in Figure 5.23. The 
components of this graphic are achieved from the list file of 
program DEMANAL after the analysis and generated by 
Microsoft Excel. The height differences and the corresponding 
number of points can be seen in this graphic presentation. The 
main point which should be analyzed in this graphic is the 
symmetric distribution. If the frequency distribution is 
symmetric, no influence of the buildings and vegetation exist. In 
this project, these graphic visualizations have been prepared 
between all evaluated models and reference models to form an 
opinion about the frequency distribution of DZ values. Figure 
10 shows the frequency distribution of DZ values between 
IKONOS and TSX SL DSMs and REFDEM. 
As mentioned before, at the accuracy analysis of heights, for the 
elimination of blunders, the maximal accepted DZ value is 
selected to 50m in program DEMANAL and the points which 
exceed this threshold value are automatically excluded by the 
program. If the image of this exception process is generated, the 
parts which are constituted by eliminated points can be seen 
clearly. By this way, these parts which have problems can be 
excluded when the models will be used for the precise 
applications. Using program DEMANAL, images have been 
created containing the excluded points. Figure 11 illustrates the 
image which contains the excluded points for IKONOS and 
TSX SL DSMs against REFDEM. The excluded points are 
represented by the dark spots. 
the accuracy analysis between IKONOS and TSX SL models 
and REFDEM. 
As expected, the IKONOS DSM shows no dependency upon 
the aspects but TSX SL DSM has a clear dependency up on the 
red arrow’s direction and differences from mean value are 
obvious. 
MEAN VALUE FACTOR FOR MULUFUCATION BY TAN(SLOFE) 
FOR INCLINATION 0 FOR AVERAGE INCLINATION 
Figure 12. Excluded points of IKONOS and TSX SL 
Besides the absolute accuracy assessments the relative 
accuracies (relative standard deviations) of evaluated DEMs 
have been identified in the study. As distinct from absolute 
accuracies, relative accuracies indicate the interior accuracy of a 
model that means a point in relation to the neighbored points. 
RSX =V E(Dxi - Dxj) 2 / (2»nx) 
RSX = relative standard deviation, d = distance between points 
dl < d < du dl = lower distance limit du = upper distance 
limit of the distance 
Figure 10. Height differences distribution of DZ between 
IKONOS and TSX SL DSMs and REFDEM 
IKONOS TSX SL 
Figure 11. Excluded points of IKONOS and TSX SL 
Besides these information’s, RMSE of evaluated models against 
reference models as a function of the terrain inclination 
direction (aspects) can be visualized using program HPSHOW. 
Especially, in SAR imagery the accuracy shows dependency 
upon the aspects. As mentioned above aspects are the functions 
of the terrain inclination direction and present information 
about the mean value, the situation for zero inclination, factor 
for multiplication ‘tan(slope)’ and for average inclination. 
Considering aspects, the most effective contents on the accuracy 
results can be appeared easily. Figure 12 shows the aspects of 
The relative accuracy is important especially for the 
morphologic details. The morphologic details for example, are 
not influenced by an error of phase unwrapping, leading to a 
local absolute error of the DSM, but not to a relative error of 
closely neighbored points. In this study, for the evaluation of 
relative accuracy, the accuracy from each point to the 
neighbored points was calculated for each evaluated DSM. For 
example, for a DSM has 3m grid spacing the relative accuracies 
were calculated between 3m and 30m at the 3m distance 
interval. The relative accuracies of the evaluated DSMs can be 
seen on the Table 6. Depending upon the reference model’s grid 
spacing, the relative accuracies have been calculated from lmto 
10m. 
Distance fm] 
IKONOS 
TSX SL 
1 
.98 
.69 
2 
1.63 
.98 
3 
2.14 
1.31 
4 
2.57 
1.57 
5 
2.92 
1.82 
6 
3.23 
2.04 
7 
3.48 
2.21 
8 
3.70 
2.37 
9 
3.89 
2.52 
10 
4.05 
2.65 
Table 6. Relative accuracies of IKONOS and TSX SL DSMs