e 12 - 
The role of analytical instruments jin the acquisition of numerica] 
information in support of off-line methods for generation of ortho- 
photos and stereo-orthophotos has been discussed in the previous para- 
graph. Systems for on-line differential rectification and printing 
that are or may be built on the principles of analytical instruments 
are offering a wide variety of interesting solutions. All of them 
obyiously hinge on the ability of the system's dedicated computer to 
control the scanning and printing mechanisms in real-time if properly 
interfaced and equipped with adequate positioning devices. 
In both man-machine and automated systems of this kind, 
besides the choice between optical and electronic printers, one can 
choose between stripwise or stationary printing techniques. Stripwise 
printing with either type of printers implies dynamic errors. Due to 
the rigidity intrinsic in optical scanner-printers, the possibilities 
for image element transformation are limited. The electronic scanner- 
printers have more degrees of freedom for the transformation of image 
elements but in stripwise printing that advantage is considerably off- 
set by dynamic errors. Consequently if stripwise printing is chosen 
for generation of orthophotos, optical scanner-printers are quite 
acceptable. The simplest man-machine configuration for on-line strip- 
wise printing and optical image transfer and modification, assuming 
that the same pair of photographs is used for observation and printing, 
would require an auxiliary optical channel for image transfer to the 
orthophoto printer and the necessary interface channels and positioning 
devices for control of the optical and mechanical components of the 
printer. Another optical channel and printer would allow for simul- 
taneous printing of a stereomate. 
Contrary to stripwise printing, in the stationary (patchwise) 
printing the dynamic errors are absent and more sophisticated transfor- 
mations of image elements are meaningful. Thus, it seems that the best 
results can be expected with the electronic scanner-printers in a 
stationary printing mode. This approach, combined with an extension of 
the concepts underlying the design principles of analytical instruments 
and automatic image correlators, lead to the construction of very 
flexible and efficient automated systems for digitally controlled gene- 
ration of pictorial outputs [16]. The two main advantages arising from 
the incorporation of the principles of analytical instruments are the 
determination of orientation parameters by least square adjustments, 
and the digital positioning control of the scanner and printer compon- 
ents. Such systems with two computer controlled printers are able to 
produce, in addition to the orthophoto generated on one printer, a 
stereomate or contours on the other, and simultaneously with these a 
digital terrain model [17]. 
Again the question of the optimal configuration and construc- 
tion of the components for orthophoto and stereo-orthophoto generating 
systems that are based on the principles of analytical instruments 
cannot be answered before a thorough study of their technical and 
economical performance, and the overall methodology of their processes 
is undertaken. 
5.4. Close-range photogrammetry 
  
The problems related to the phenomena dealt with in close-