Fig. 2. Multiplex for training in the laboratory and at the fieid survey camp. 
tion. Two ordinary projectors are used together with a third one for 
the floating dot. 
The projectors can be oriented with sufficient accuracy for stereo- 
scopic projection of aerial pictures or terrestrial pictures, taken with 
ordinary single cameras. The polaroid filters are used for the image 
separation. The stereoprojector has proved to be of great value for the 
photogrammetric instruction. Several fundamental photogrammetric 
operations can easily be demonstrated for a large group of students. 
"n 
  
  
Fig. 3. Transport box for the Multiplex.