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4 . Automatic Height Measurements 
Automatic image correlation and automatic height measurements are other 
important elements in the new conception of photogrammetric image restitution. 
In these fields, developments are still going on. The first operational system for 
automatic height measurements and production of orthophotos was developed by 
Hobrough in the seventies. Some image correlators had already appeared on the 
market earlier, but their possible applications were very limited. Most of these 
early processors were based on analog procedures which did not provide suffi 
cient flexibility. 
More favourable conditions are offered by the various digital procedures and most 
of the research in photogrammetry is currently concentrated in this field. 
Apparently, operational procedures might already be available for industrial 
applications (cf. [2]). Interesting procedures are also available for small scale 
plotting and automatic height measurements from satellite images (cf. [3]). 
Large scale mapping, however, entails much more difficult conditions. 
In recent years, the Institute of Photogrammetry of the EPF-Lausanne, in collab 
oration with Kern & Co., has worked intensively on this problem and all tests 
indicate that the procedure being developed will satisfy the requirements in prac 
tice. The most important difficulties for the automatic derivation of a digital ter 
rain model are the development of robust algorithms for image matching, the 
assurance that the measurements are effectively carried out on the natural ter 
rain and the development of procedures allowing for thorough control of the 
results with appropriate possibilities for editing. 
The image correlation elaborated at the Institute of Photogrammetry uses Multi- 
Templet Matching, an algorithm developed from dynamic programming. This 
process is based on the computation of height parallaxes of image segments of 
varying size. The parallaxes are introduced into an adjustment algorithm which 
approximates the terrain with the help of finite elements. According to this ter 
rain approximation, the aerial photographs are resampled and the height corre 
lation is iteratively refined (cf. fig. 3). In order to accelerate the computations, all 
image operations are done on an array of Transputers. In a subsequent phase, 
the terrain obstacles are eliminated by a special filtering process and the data are 
finally controlled by image injection in an analytical plotter. Various tests have 
shown that a precision of the order of 0.1 %o of the flying height can be obtained, 
even with photographs of rather poor contrast and a terrain cover by houses or 
trees of up to 30% can be automatically eliminated. With the current technology, 
about 12 hours are still necessary for a model, but the new generation of 
Transputers should considerably reduce the processing time. This procedure 
would allow one to significantly reduce the cost of the establishment of digital ter 
rain models and that of the the production of orthophotos, which could then serve 
as a base for other tasks in photogrammetric production. 
5 . Conception of Future Mapping Systems 
These various new elements for image measurements and image analysis enable 
us to foresee new and more versatile systems for photogrammetric production. 
The most spectacular development is the transition from analog to digital ortho 
photos. Along the same lines, it can be expected that purely digital plotters be 
introduced into the practice, but a much more interesting development will be the