As noted. in an earlier section, the plotting speed is 
automatically controlled as a function of measured cross- 
correlation and x parallax errors. Also, when the parallax 
error values exceed predesignated limits, the stylus is raised 
until acceptable error limits are regained. If correlation 
falls below an acceptable value, the stylus is raised and the 
computer commands a local search for re-establish the plotting 
line at some nearby point. The coordinates of the end of the 
gap, i.e., the point at which automatic plotting is resumed, 
are automatically recorded for use during later manual fill-in 
operations. 
c. Profiling Mode - The automatic profiling mode 
produces profile charts which are automatically drawn by 
the coordinatograph for a selected profiling direction within the 
model. To initiate operation in this mode,.the profiling-mode 
tape is entered, and the desired profile direction, profile 
interval, coordinatograph index offset, plotting boundaries, and 
output plotting scale are entered from the viewer panel.  Auto- 
matic profiling can be started at any point in the model. The 
detailed operation in profile compilation is similar to that 
for contouring except that automatic indexing is performed only 
at the plotting boundaries. 
d. Orthophoto Mode - In the orthophoto mode, ortho- 
photographs and form-line contour charts are compiled on photogra- 
phic film on separate stages in the printer. 
  
To initiate operation, the orthophoto-mode tape is entered, 
and the desired values for the profile interval, model boundaries, 
output plotting scale, contour interval, and contour reference 
elevation are entered from the viewer panel. Orthophoto compila- 
tion is started in one corner of the plotting area. Profiling is 
performed in the Y-direction, with the X-direction indexing at 
the plotting boundaries. In regions which are not plotted, the 
coordinates of both ends of the gap are recorded for later use 
in fill-in operations. 
The video signal for the orthophoto is normally selected 
from the photograph whose nadir point is nearest to the compilation 
point. This procedure improves resolution and minimizes local 
image distortion in the output orthophoto. Automatic switching 
from one video signal to the other is performed by the computer 
at the mid-point of the air base. Dual sets of video controls 
are provided to compensate for differences between input photo 
densities and to unify the output density characteristics across 
the transition region. 
e, Fill-In Mode - As discussed in the preceding sections, 
those portions of the model that contain insufficient or uncorrela- 
table image information are left unplotted and their locations are 
automatically recorded when correlation is regained. In the fill- 
in mode, the gaps created by this procedure are plotted manually 
to complete the output record. 
30