PHOTOGRAMMETRIC ENGINEERING 
of dual scanning tubes; and because the free 
movement of the tracing table minimized the 
inertia to be overcome in the scanning 
carriage. In the B8-Stereomat, shown in 
Figure 3, the projectors were redesigned so 
that the space rods guide the diapositives 
(which are lighter than the scanning system) 
while the optical and electronic parts of the 
scanning system are stationary. The CRT 
assembly details are shown in Figure 4. Al 
though the measuring accuracy of the in 
strument suffers by moving the diapositives, 
the mechanical response is increased and 
complete freedom is allowed in the design of 
the scanning system. 
The B8-Stereomat, unlike any of the 
previous Stereomats, has been equipped with 
a device to produce orthophotographs. This 
is possible in this instrument because the 
large optical aperture has greatly improved 
the signal-to-noise ratio over previous models. 
To produce the orthophotograph the model is 
profiled as discussed above in differential 
rectification. Here however, the area scanned 
is transmitted by electrical signal and pro 
duced on the screen of a third cathode ray 
tube which prints the orthophotograph. The 
amplitude of the current from one to the two 
scanners controls the intensity of the beam 
and thus the recorded photographic image. 
The scale of the image is charged electron 
ically as a function of the instantaneous 
height of the space rod intersection. Since the 
scanning tube spot is imaged at reduced scale 
on the diapositive and the area scanned is 
small, the resolution of the televised image 
on the printing tube can be increased to avoid 
loss of detail. 
The operational modes of the B8-Stereomat 
are manual, A-profile, orthophoto printing 
mode (A-profile), T-profile, contouring mode 
and automatic orientation. In the manual 
mode the space-rod carriage can be moved 
freely by the operator. In the A-profile mode 
the Z-transport is driven to zero by the A- 
parallax, while the space-rod carriage is 
driven in the A-direction and stepped in the 
F-direction. The tracing speed is controlled 
by the correlation signal. The A-profile mode 
is used to obtain an orthophoto print. The F- 
profile mode is identical to the A-profile mode 
with the A- and F-drives interchanged. In 
the contouring mode the space-rod carriage 
is driven in the A- and F-direction to null the 
A-parallax with the Z-drive unchanged. The 
nulling operation is performed along the 
gradient and the trace velocity along the con 
tour is proportional to the correlation. The 
automatic orientation mode is used to rela 
tively orient two plates. After the F-parallax 
in the Kappa stations are zeroed, the space- 
rod carriage moves through a programmed 
sequence of orientation stations removing 
F-parallax at each by the appropriate mo 
tion. The Z-carriage is used to remove A- 
parallax at each station. Again, the speed of 
operation is determined by the correlation 
signal. With the model and orthophoto scale 
of from 1.4 to 2, the average speed of profil 
ing is 7 mm per second. Orthophoto prints 
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