however only after having enabled this by OPEN OBJECT. "Open an object" 
means that control is given to RTR1 (Fig. 3) and into the last object 
in the buffer. CLOSE OBJECT returns control to RTRO. Inconveniencies 
can arise if objects further ahead in the buffer have to be edited. In 
order to get there, all other objects till the end of the buffer must 
be deleted in the present system. It is intended to overcome this de 
ficiency by means of a special "by-passing" or "identifying" function. 
Data already stored on tape file are considered error free within the 
mensuration phase. 
CONCLUSIONS AND PROSPECTS 
Although the experimental set-up is still under development, first 
applications to land use planning surveys have indicated the flexibili 
ty of the system in principle. It allows for a user-friendly digitizat 
ion of photogrammetric data with simple and fast editing capabilities, 
thus representing an important link in the total chain of photogramme 
tric stereocompilation. However, problems associated with compatibility 
with other systems, data transfer speed and storage capacity, optimal 
data entry for feature names, and further interactive graphics data pro 
cessing, still have to be solved. It seems, though, that the total 
photogrammetric digitization system comprising all three phases will 
be less complicated than generally assumed. 
ACKNOWLEDGEMENTS 
Research leading to this paper was mainly supported by Deutsche For 
schungsgemeinschaft (grant no. 220/2+). The authors are indebted to 
Dipl.Ing. Jacobs for his vehement engagement in adapting the system to 
an interesting application in land use planning.