In spite of the large number of unknowns the numerical 
effort for solving the normal equations therefore is relatively 
small and practically independent of the number of control 
points. With a medium fast computer the computing time will 
be within a few seconds for an image of several thousand 
lines. (For further advice see /2/). Moreover this amount 
for estimating the exterior orientation parameters is small 
compared with the ensuing rectification procedure. 
Rectification is called the operation, which transfers 
every single picture element from its actual (wrong) 
position to the real (correct) position. 
CONCLUSION 
The presented model for geometric rectification of remote 
sensing imagery presently is under investigation in re- 
gard of achievable accuracy as a function of the number of 
control points used. In the second step the developed 
computer program shall be applied to practical scanner data. 
The necessary terrain height information then will be 
derived from digital terrain models (DTM). The DTM as well 
as the control points, necessary to meet pregiven accuracy 
requirements, can successfully be obtained from photo- 
grammetric flights over the scene area. 
REFERENCES 
/1/ Ebner, H.: A mathematical model for digital rectifi- 
cation of remote sensing data. Paper presented at the 
XIIIth Congress of the International Society for 
Photogrammetry (Comm.III), Helsinki 1976. 
/2/ Ebner, H. and Hossler, R.: The use of Gauss Markov 
Processes in Digital Rectification of Remote Sensing 
Data. Paper to be presented at the ISP-Comm.III - 
Symposium, Moskau, July 31 - Aug. 5, 1978.