are many photographs covering alarge area, 
the available data are usually input to a 
“block adjustment” program on a larger 
computer where they are handled on a si- 
multaneous basis to obtain the best fit for 
the complete set. The output of these pro- 
grams is a set of tapes, one for each dia- 
positive, that provides an adequate mathe- 
matical description of the diapositives. 
Before the compilation or altitude mea- 
surement can proceed for each stereo 
pair, an auxiliary set of tapes describing 
the desired compilation is made. These 
include a specification for the geographic 
area to be included in the measurement, 
the scale of the desired output product, 
the desired contour interval, and a list 
of geographic coordinates of points to be 
marked on the output product (such as 
map grid coordinates and geodetic con- 
trol points). 
Compilation of a given stereo pair is 
Started by mounting the diapositives on 
the two selected tables, the unexposed film 
sheets on the other two tables, and a print 
corresponding to one of the diapositives 
on the reference viewer. The switches on 
the control panel are set in accordance 
with the table assignments, and the dia- 
positive to be used in preparing the ortho- 
photo is selected. The two diapositive 
tapes and the compilation tape then are 
read into the computer. 
When the tapes are entered, the COM- 
PILATION indicator lights and the two dia- 
positive tables move to the indicated position 
of a first- measurement point to be used in 
determining the orientation of the photo- 
graphs on the table (usually a camera 
fiducial mark). The operator uses the 
position control to accurately center the 
selected mark on each diapositive, then 
signals the computer via the keyboard to 
move to a second mark where the opera- 
tion is repeated. The computer uses the 
resulting data for "interior orientation;" 
i.e., to relate the coordinate systems of 
the diapositives to the coordinate systems 
of the respective tables. As a check on 
e 
this operation, the computer uses the geo- 
graphic coordinates of an easily recognized 
control point to calculate the coordinates of 
the corresponding image points and then 
centers the tables on the calculated posi- 
tions. If the operator observes the control 
point to be well centered on the reference 
mark, he signals the computer to proceed. 
If it is not well centered, the operation is 
aborted and various phases are repeated 
until satisfactory centering is observed. 
The operation provides a simultaneous 
check of the diapositive data and the set- 
up measurements. During the setup oper- 
ation, the operator indexes the photo print 
on the reference viewer so that the print 
provides an accurate indication of the posi- 
tion of the field of view. 
If the operator signals a satisfactory 
orientation, the equipment prints out the 
designated symbols on the output film 
sheets. 
At this stage, the operator may choose 
to delineate potentially troublesome regions 
within the area to be compiled. This is 
accomplished by placing (using the position 
control) the light on the reference viewer at 
a low point on the region to be defined, 
depressing a button to designate the auto- 
matic action to be taken in the region dur- 
ing compilation, and then (using the position 
control) moving the light on the viewer 
around the boundary of the region to be 
delineated. When the operation has been 
completed, the operator may choose to 
describe other regions or to proceed with 
the compilation. 
Routines available for this “adverse- 
area” operation include slowing down for 
difficult areas, ignoring indicated altitude 
changes (for use over large bodies of 
water), and stopping after moving out of 
an area to permit the operator to make an 
altitude correction (such as might be re- 
quired in moving over a cliff). It is an- 
ticipated that the available routines will 
be augmented as experience indicates other 
desirable modes of operation.