Full text: Proceedings of the Symposium "From Analytical to Digital" (Part 1)

  
superior to those obtained with the affine transformation. 
RESULTS OF THE DEVLR DIGITALLY PROCESSED IMAGERY 
The accuracy figures obtained after testing this imagery are shown in 
Table (5). Close inspection of the figures on this table shows that 
for both the control and the check points there is a gradual but 
insignificant deterioration in accuracy as the higher order terms are 
truncated. The linear conformal transformation gave nearly the same 
results as the affine or h-term solutions. It is noted that the results 
of the control and check points on this image are more consistent than on 
the RAE image. 
A noticeable feature of the residual errors on all images is their very 
highly systematic nature, though to a lesser extent on the optically 
processed images. As will be noted from the vector plots of'Figs. 5 to 
12, the majority of these plots point in the cross-track direction of 
the image either inwards or outwards. This strongly suggests the effect 
of variations in topographic relief on the geometric accuracy of the 
images. It is indeed possible to eliminate or reduce the effects of 
these relief errors by digital monoplotting techniques using a digital 
terrain model (DTM) which could be generated from digitizing topographic 
maps of the area (see Ali, 1982). This, however, has not been implemented 
in this particular experiment; but has been reported on in another investigation 
by the present author (see Ali, 1985). 
SUMMARY OF THE GEOMETRIC TESTS AND CONCLUSIONS 
(i) Metric imformation with an accuracy standard compatible with 
very small scale planimetric mapping can be derived from satellite 
SAR imagery using both optical and digital processing techniques. 
(ii) Interpretation of features for the purpose of selecting suitable 
ground control points was very difficult on all images but in 
particular on the optically processed ones. On the two digitally 
processed images, the background clutter was such a feature that 
positive identification of objects was in many cases impossible 
without the consultation of the map. 
{1443 The optically processed images supplied by ERIM contain substantial 
scale errors. The effects of those errors are largely reduced 
when a higher order polynomial is ultilized. In contrast, the 
digitally processed images suffer less from those scale errors, 
Hence inclusion of higher order terms in the polynomial did not 
improve the accuracy significantly. 
(iv) Although the two digitally processed images of the test area have 
been processed using similar processing techniques, it seems that 
the geometric fidelity of the DFVLR image is much superior, as can 
be noted from the accuracy figures obtained with this image. 
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