e 
MATRA OPTIC 
DESCRIPTION OF TRASTER 
  
As mentioned previously, one of the fundamental features of 
the TRASTER is the system for displaying the stereomodel on 
a screen. Each of the photographs is projected on the screen : 
in polarized light.  Stereoscopy is obtained bv observing the 
screen with a pair of glasses with polaroid filters crossed 
at 90 degrees, and with an orientation corresponding exactly 
to the orientation of identical filters inserted in the op- 
tical projection path of each of the photographic images. 
This arrangement permits total freedom of the operator's 
head. Viewing the stereomodel at a finite distance elimin- 
ates change in visual accommodation imposed upon operators 
observing exposures through binocular lenses as on conven- 
tional stereoplotters. With binocular lens observation oper- 
ators must accommodate constantly between the infinite focus 
Of optical systems and a finite distance in order to look at 
paper prints of the pair of exposures being used, the computer 
readout, the drawing table, etc. 
Viewing on a screen is thus less tiring for the operator. 
Several other favourable aspects of this means of viewing may 
also be cited, for example: 
- the operator-to-screen distance is not set. A normal dis- 
tance of about 500 mm corresponds to an apparent enlarge- 
ment of about half the enlargement of the image on the screen. 
If the operator approaches the screen, the apparent enlarge- 
ment increases and permits better plotting accuracy. 
- several operators may observe the stereomodel at the same 
time. Thus, in the event of doubt as to analysis or identi- 
fication of details, the operator can ask another person for 
his opinion without interrupting his stereoscopic examination. 
Quite obviously, this possibility thus offered to several 
operators to view at the same time greatly facilitates operator 
teaching and training. 
- psuedoscopic viewing is obtained without complicated and costly 
permutation of the optical path. It is sufficient to use a 
second pair of glasses with reversed polarized filters. 
Detailed Description of TRASTER 
  
TRASTER is proposed as a basic appartus assembling common func- 
tions with various optional equipment. The apparatus will be 
described as follows: 
— basic traster 
- graphical version 
- numerical version