Fig. 1 Schematic diagram of 
Planimat projection system. 
  
  
  
  
  
Fig. 2 Uses of the 
straight mechanical 
guide rod in photo- 
grammetric plotters 
a—c double-arm 
d—g single-arm 
h,i design using one 
or two space 
points 
    
©) 00 oO) | D, DA) 
e oC) e a) O O 
aM wn » 
2e 2f 
2a 2b 2c 2d 29 2h 2i 
or 2i were chosen for the Planimat. This selection was determined by several considerations which will 
here only be indicated by the terms: counter-balancing, deflection, limitation of focal-length range and 
integral tracing table. 
As regards deflection, the single-arm guide rod is superior to the double-arm rod, since the load of 
the image-plane carriages is not applied on the projecting portion as in the double-arm rod, but be- 
tween two "fixed" supports (G and P). Consequently, use of the single-arm rod is simpler for long 
focal lengths on the one hand and for wider field angles on the other. 
Supporting the end of the rod at G makes it possible to provide a drawing plane directly in the 
instrument, without any opening for the guide rod. 
The use of two space points permits very small bx-values to be introduced, including the value 
bx — 0. Moreover, it facilitates the empirical process of relative orientation, since bz and by may be 
introduced in the second operation. Most important of all, this solution does not require the rotation 
of the great mass of the two cameras about a common axis (common 9), which frequently presents a 
problem in view of the required accuracy. 
Fig. 3 illustrates the disposition of the plotting cameras, showing only one side as an example. As 
is evident, the camera with the photo-carriage W, the image-plane reference point D and the per- 
spective center P is pivoted at the Cardan point K. The rotation is caused by the y and « setscrews. 
Fig. 3 also shows that the viewing optical system is stationary — leaving aside the effects of p and w — 
and that the guide rods L shift the photos Dy. 
194