40 
2, 
  
  
  
  
  
A more satisfactory way of generating a DTM is to use a ste- 
reoplotter which has been equipped with digital encoders on 
the X, Y and Z axis. 
The stereo plotter must have a means of preparing a graphic 
which will show where the stereo model has been digitized. 
This procedure does not have the mechanical guides that one 
has when digitizing in the profile mode. 
The sharp drainage should be digitized first followed by sharp 
ridges. The area between the drains and the ridges is filled 
in using a technique which is somewhat like contouring. See 
Fig 2, 3 and 4. The Z of the stereo plotter is set at an arbi- 
trary setting preferably at the low elevation of the stereo model. 
The graphic trace is engaged and a reading is made whenever 
the trace of the terrain changes direction. After one level 
has been completed, the Z is raised up an arbitrary amount and 
another level is digitized and traced. By inspecting the graphic 
trace of where the model has been digitized, one can judge where 
the terrain is not fully defined and additional points can be 
read. 
  
  
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