-4- 
(with proper amplication) is used to drive the appropriate orientation motors 
to zero any Y aprallax between the plates during the automatic relative 
orientation procedure. 
The X parallax signal, after further amplication, is used either to drive 
the Z carriage up or down, as in the manual and profiling modes, or to drive 
the space rod carriage in the X and/or Y direction, as in the contouring mode, 
to null the X parallax. 
(c) Slope Signal: 
Should both CRT's scan areas of no X parallax in the centers of the 
patterns, there can still be X parallax away from the centers due to local 
scale changes caused by model slope. The scan, consisting as it does of an X 
and Y random noise signal superimposed upon a slower circular scan, will 
then cover each parallax area once for each circular scan and thus sense posi 
tive and negative parallax once each circular scan. Therefore, it not only 
indicates the magnitude of the slope but the direction as well. Thus, the X 
parallax signal contains a component in the circular scan frequency that is 
proportional to the tangent of the model slope. This slope signal is used in the 
correction computer C to adjust each scan for these local scale differences 
and in effect, optimizes the correlation across the whole scanned area. The 
slope signal, having a direction as well as an amplitude, can be used in the 
contouring mode to steer the space rod carriage back to the contour and so 
to zero the X parallax. This, however, sets a limit to the degree of slope com 
pensation that can be used, resulting in a degradation of the slope signal and 
consequently the steering signal. In Stereomat B-8 a feedback factor of 10 has 
been used for nulling the slope signal. 
The proper operation of Stereomat is dependent upon attaining optimum 
correlation under all conditions so as to have maximum X parallax sensing 
ability and thus to limit the dynamic error. For this purpose any local scale 
differences caused by tip, tilt, or terrain slopes have to be removed. In order 
to do this, the relationship between an object in the stereo model and its pro 
jection on the plate, as changed by tip, tilt, or slope, has to be known. This 
relationship is employed to obtain an appropriate change in the pattern used to 
scan this plate. 
If we call the projection of a line segment in the X direction (in the model) 
AX q , in the Y direction AY ; the projection on the diapositive in the X direction 
AXi and in the Y AY± , thei? the following relations exist: 
AX : 
AYx 
F 
1 
ÎAXoU 
Z 
o 
(1 + cp tan oc + 
uo tan 3) a 
F 
1 
K« 1 
Z 
o 
(1 + cp tan cc + 
uu tan 3) 2 
+ U) tan 3 - tan 0 tan a) 
x 
- AY (a) tan a + tan 0 tan cc[ 
o v Y J 
+ cp tan a - tan 0 tan 3) 
y 
- AX (cp tan 3 + tan 0 tan 3 
O X 
O