Until 1979, relative and absolute orientations were made using the well- 
known standard procedures for analog instruments. 
After completion of the map in 1979, we started to concentrate on the 
revision process in order to speed it up and to optimize the adopted 
solution. Stereo-restitution for revision work is somewhat different 
from restitution work for new maps: 
- The restitution has to fit into an existing map-framework. In order 
to maintain a homogeneous map quality over several revision periods, 
the control and maintenance of the accuracy standards become very 
important. 
- The originally restituted information must be in an adequate form, to 
be used not only in the primary scale (1:25'000) but also in the 
smaller scales. 
- The relation between orientation and restitution becomes quite 
unfavorable. In many cases the information content per model is very 
small. On an average, an operator can manage to restitute 1 to 3 
models per day. 
An analysis of the revision process with respect to photogrammetry 
resulted in the following possibilities for improvement: 
- Building up a control-point net covering all of Switzerland by means 
of aerotriangulation, using natural fix-points (crossroads, houses, 
large boulders, etc.); average RMSE in planimetry and height : ±1 m. 
- Numerical orientation for analog instruments to control the fit and to 
decrease the time required for the orientation. 
- Digital plotting to improve the use of the revision elements in the 
smaller map scales. 
In view of the current developments (digitization), the available work 
capacity and for internal reasons, we decided to realize the numerical 
orientation as a first step. 
3 Numerical orientation 
3.1 Hardware 
Fig. 1 
Hardware configuration