Figure 4: Avenue 
rantee a distinctly different background color. The transpa- 
rent pixels can then be separated by image processing tools. 
The use of the billboard method for hedges is suggested and 
will be tested. For objects with big spatial extension like 
woods or corn fields combining texture information from 
aerial photographs for the upside and texture information 
from terrestrial photographs for the vertical sides is the first 
attempt for visualisation. Further methods with even more 
effort in geometric modeling will be examined to find out 
which results are preferrable. 
Besides the modeling of the objects, special methods of 
computer graphics have to be considered to achieve a highly 
realistic representation. For example, natural phaenomena 
like depth cueing and fog, or the change of lighting due to 
clouds can be introduced. Global rendering methods like 
ray-tracing should be used to make visible effects like 
shadows or reflexions. 
The intensive use of phototextures together with global 
rendering methods can result in some absurdity, as the 
direction of the light is implicitly contained within the 
phototextures through shading.What is more, shadows of 
trees modeled as billboard planes can be reduced to a line 
when the angle between the viewing direction and the sun 
direction is about 90 degree. Thus additionally effort in 
geometric and radiometric modeling has to be made to reach 
photorealistic visualizations. 
  
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6. CONCLUSIONS AND OUTLOOK 
The proposed approach for the derivation of photorealistic 
representations of real landscapes, based on enhanced digi- 
tal orthoimages and textured 3D objects is useful for the 
visualization of currently existing landscapes. Changes in 
the projecting 3D objects like the growing of plants or new 
buildings can also be represented without special efforts, 
because the proposed methods can be used. 
When results of a planning change the objects represented 
by the texture of the orthoimage, new methods have to be 
developed for the photorealistic visualization of these ob- 
jects. During the course of the planning the texture of the 
orthoimage more and more will be replaced by the repre- 
sentations of accurately designed objects. 
As explained above photogrammetry is the most important 
method of data capturing for this purpose. The requirements 
are best achieved by digital photogrammetric systems 
(DPS). Adding visualization tools could be a self-evident 
expansion of DPS. These systems need strong graphical 
power for the stereo viewing of digital image pairs on the 
one hand and contain the methods of digital photogramme- 
try mentioned in section 4 on the other hand. The stereo 
cabability of DPS can be used to represent stereoscopic 
views of the landscape which will improve the evaluation 
of planning tasks. Thus synergy can be expected running 
digital photogrammetry and 3D computer graphics on the 
same high-end graphical workstations. 
Nowadays real time and photorealistic visualization at the 
same time is only imaginable using high-end graphical 
computer. But it is predictable that future generations of 
graphical workstations will be able to meet these conditions. 
Then interactive planning tasks could be made in real-time 
at the computer (Ware, 1994) demanded by people using 
facilities of virtual reality like stereo projection systems. 
7. ACKNOWLEDGEMENTS 
GIS, DEM and aerial photographs have been provided by 
the Lehrstuhl für lándliche Neuordnung (Chair for land 
consolidation), Technische Universität München. 
The practical work for these examinations was best suppor- 
ted by the staff and facilities of the Institut für Computer- 
unterstützte Geometrie und Graphik, Technische Universi- 
tät Graz. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996