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and editing on-line photogrammetric system (e.g. the photo points can 
be directly addressed from the display screen). The only shortcoming 
of this configuration is that the digitized features are not displayed 
in the field of view of the instrument. A new device, the position 
verifier, has been developed for this purpose [8]. An auxiliary 
carriage is slaving the movements of one of the instrument's photo 
stages. The digitized features are graphically recorded on an electro- 
sensitive printing material placed on the auxiliary carriage. That 
graphical record can be displayed at will via an auxiliary optical 
channel into the main optical train of the instrument. Since the photo- 
stage of an analytical instrument moves only in its own plane, the dis- 
played line-drawn record will be seen stereoscopically when super- 
imposed over the observed stereo model. Considering that the poten- 
tials for automation of interpretation and line digitizing of man-made 
and natural features are virtually nil, the use of these digitizing 
and editing aids on analytical instruments are expected to have deci- 
sive influence on the development of efficient digitizing procedures. 
Some other numerical output forms are used primarily as the 
storage medium for intermediate digital information needed at later 
stages of processing in the photogrammetric systems themselves. The 
main examples are the digitizing of profiles and the generation of 
digital terrain models. Besides their direct use in cartographic and 
engineering applications, this digital information is mainly needed for 
on-line or off-line generation of orthophotos, stereo-orthophotos, 
contours and cross-sections. For these cases the digitizing on analyti- 
cal instruments can be performed in a manual, a semi-automatic or an 
automatic mode. Since these digitizing operations are well suited for 
automation due to the relative simplicity of the underlying mathematical 
models, only the two latter modes are of interest. 
The semi-automatic mode implies automatic guidance of the 
measuring mark in pre-determined patterns and the automatic recording 
of heights determined by the operator. Computer controlled guidance 
allows for a free choice of digitizing patterns and recording techni- 
ques. By inclusion of simple subroutines into the basic real-time 
programs many variants of the compilation programs for semi-automatic 
scanning and digitizing are available. There is a choice of time or 
incremental mode with free choice of scanning speeds, and recording 
frequencies lower or equal to the execution time of the basic real-time 
program. The execution time, being much shorter than the operator's 
response time, does not pose any limitations. Instead of continuous 
movement of the measuring mark it can be made to advance in jumps. The 
recording and the subsequent jump may take place automatically after a 
preset time delay. During that delay the operator is supposed to remove 
the horizontal parallax. A more sophisticated semi-automatic variant for 
selective digitizing in grid patterns may be so organized that the 
digitizing is performed first in a low density grid with large coordi- 
nate increments. The compilation program then analyzes the digital 
model and determines the areas requiring more height information. It 
then accordingly decreases the coordinate increments for the higher 
density grid and addresses the selected positions in which the operator 
performs the height measurements. After the second set of data is added 
to the previously recorded one, a new check is made by the program and 
the iterative procedure is repeated until the check confirms that the 
preselected standards are met and that the smallest forms of the ground