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price and intended use. 
Off-line versus on-line production of orthophotos. 
  
The off-line approach is supported by many appeal- 
ing arguments. Some of these are the use of any available 
plotters for production of profiles, elimination of pro- 
filing errors, rapid orthophoto printing process and conse- 
quently achieving a more efficient and economic operation, 
and the possibility of using existing terrain data for any 
future orthophoto work (updating of orthophoto products). 
Probably the most appealing are the economic and technical 
advantages offered by the possibility of introducing into 
the orthophoto printing process intermittent profiles, in- 
terpolated from the available profiles. In this connect- 
ion, the more final solution would be to. use contour lines 
as the basic input from which profiles of any density could 
be construed as required by the orthophoto printing process, 
The off-line systems are however relatively expen- 
sive as far as initial investment is concerned and there- 
fore are not in financial reach of smaller photogrammetric 
operators, often concerned primarily with a limited volume 
of the work. Also, some of the technical arguments sup- 
porting the off-line approach may lose their validity or 
become insignificant. I am referring here to the inac- 
curacies of profiles in on-line operations. À simple pro- 
file follow-up system as developed by Galileo may be a 
partial remedy. Another significant improvement is the 
introduction of the continuously variable speed of pro- 
filing, to be adjusted constantly at the operators discre- 
tion. 
Further, some of the on-line orthophoto facili- 
ties are developed as the attachments which can be added 
to existing plotters (SFOM Orthophotograph 693, Wild and 
Galileo systems). In such cases, the capital investments 
are relatively modest and the fact, that for a limited ex- 
pense one can get equipped for both, conventional mapping 
and orthophoto production is not without importance, 
particularly for small users. 
It would also appear that there should be no need 
for a rigid separation between on-line and off-line systems. 
This is, for example, the case with the recent development 
by Kelsh Division and partly, at least, by Matra (SFOM). 
It is also quite obvious that the last word in this regard 
has not been spoken yet and various interesting solutions 
are conceivable. The crucial factor seems to be the cost 
of the peripheral equipment necessary to add an off-line 
characteristic to the on-line system, but one is witnessing 
quite a dramatic development in the field of technology 
concerned which may greatly facilitate a hybrid solution. 
  
  
  
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