4,2 Correlation results 
test site points avg. oorr. low corr. failures 
0.6 «r «0.7 
Landshut 31200 0.84 7% 2% 
Deggendorf 900 0.87 2% 0% 
Vilsbiburg1 625 0.86 6% 0% 
Vilsbiburg2 625 0.89 51 0% 
Table 2 : Correlation results 
The results of the correlation runs are listed in tab. 2, whereas 
fig. 6-12 show the perspective presentation of the heights.Fig. 5 gives 
a copy of the image content for test site Landshut. 
Examinating the results in tab.2 it is obvious, that the image content 
provided enough information for the correlation. The high level of the 
average correlation coefficient as the small number of failures proves 
the success of the calculations. The existence of failures for test site 
Landshut might be caused by the errors in the orientation parameters, 
which led to y-parallaxes in some parts of the covered area. 
However, the value of the correlation coefficient doesn't say anything 
about the quality of the resulting heights. Likewise the perspective 
presentation in fig.6 shows some mostly isolated peaks, which doesn't 
match the adjacent height level. These wrong calculated heights belong 
to the problem of gross errors, which sometimes occur in the correlation 
process. Due to the manifold reasons responsible for this effect the 
phenomen can't be easily suppressed. On the other hand the quality of 
the calculated heights is reduced at all. 
To improve the results and to eliminate obviously wrong heights the 
calculated data will be filtered. Using a non-linear, noise reducing 
filter like a median working in a 3*3 window, the updated heights look 
as fig. 7 shows. The improvement is impressing and the plot now clearly 
repoduces the topography of the surface without disturbing influences. 
To establish the amount of correction the calculated as the filtered 
heights were compared with the heights of the reference DTM. Table 3 
gives the results. 
compared heights 
test site correlated - refer. DTM filtered - ref. DIM 
Deggendorf 40 31 
Vilsbiburg1 34 19 
Vilsbiburg2 25 15 
Table 3 : Mean square height residuals in m 
The improvement ranges from 21% to 46% and proves the validity of the 
filter process. One important reason for the effectiveness of the median 
filter in this context is, that the gross errors mostly occur isolated 
what gives them the characteristics of noise. 
As visual examples the correlated, reference and filtered heights are 
given for test site Deggendorf in fig. 8 - 10. It is satisfying to 
realise the correspondanoe in the relief structure for the filtered and 
reference heights. 
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