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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
average flight line 1 
->o 
average flight line 2 
intercept of both flight lines 
Figure 5: The displacement of object points above the reference 
plane referring to its position in terms of distance to the related 
flight line 
The dislocation of a point depends on the height of the flight, 
the point height (distance from reference plane) and the 
distance of the point from the related flight line. The object 
height, the only unknown, is estimated roughly and is used to 
estimate the maximum displacements in order to optimize the 
range to be searched in. Thus, the ambiguities and the 
processing time get significantly smaller. 
Figure 6: Fusion of the two input images 
Figure 7: Median-filtered result of the correlation with template 
sizes from 3x3 to 9x9 pixels 
In Figure 6 one can clearly recognize the displacement of 
building edges in vertical direction. In Figure 7 it can be seen 
how the double displayed building edges are corrected to one 
line. To close single missing pixels the result image has been 
filtered with a median filter of size 3x3. The ambiguities, which 
can't be excluded totally and the simplifications made in the 
beginning are the reasons for some loss of accuracy resp. 
sharpness. 
6. CONCLUSIONS 
The new approach for the generation of true orthoimages has 
been tested with real data. The simple image and recording 
geometry, which was earlier assumed in simulated studies, gets 
lost if real image data from an airborne pushbroom scanner are 
concerned. Several factors lead to variations from the ideal 
flight conditions. For this reason some pre-processing of the 
raw data is necessary. This prepares the basis for the 
determination of corresponding points and the extraction of true 
ground information. 
A characteristic property of the data is the permanent change of 
orientation parameters for any scanned line. Related 
assumptions have been defined and corrections have been 
introduced. From the study it turned out that the image data was 
suitable, because only minor deviations from the ideal 
configuration occurred. Thus, the investigations of the 
geometry and the implementation of automatic correlation 
confirmed generally the practicability of the new approach. 
However, more detailed studies and the development of 
effective matching procedures are necessary for future deve 
lopment. Then it can be expected, that the method offers a 
reliable and very productive alternative option to generate true 
orthoimages. Particularly, the independence from elevation 
models and the possible improvement of the visibility of occlu 
ded areas in certain urban regions are significant advantages.