Interior orientation is then performed by measurement of the
fiducials, and the computer automatically computes and stores
the photo principal-point locations, A control-program tape
is then entered to establish operation in the desired operating
mode.
a. Orientation Mode - The orientation mode provides
relative and absolute orientation of the stereo model. This
mode is employed when a given stereo pair is being processed
for the first time. If the model has been previously oriented,
it can be recovered by reading a tape which contains the
orientation parameters.
In relative orientation, the values of the camera focal
length and the correction coefficients are first entered from
the viewer panel. The orientation errors are then determined
from measurements of y parallax made automatically at from 5
to 12 points in the model. At each point, the correlator outputs
are used by the computer to automatically eliminate elevation
error and y parallax. The y parallax is eliminated by inserting
a differential y displacement of the two photographs. During
this process, the amount of motion required is recorded as the
y parallax, After these measurements have been made at the
desired points, the computer calculates and stores in appropriate
locations the necessary changes in the values of the orientation
elements.
Absolute orientation is based on the known model coordinates
of three or more control points. The known coordinates of each
point are sequentially entered through the viewer panel while
the corresponding coordinates in the unoriented model are being
measured, using the correlator outputs to clear the elevation
error. When this procedure is completed, the computer determines
the required changes in the orientation elements to level and
scale the model. If more than three control points are used, the
leveling and scaling computations minimize the mean-square errors
at all control points. If desired, the residual errors at the
control points can then be used to define the coefficients of the
model-deformation correction.
b. Contouring Mode - The contouring mode produces con-
ventional contour manuscripts that are automatically plotted on the
coordinatograph. To initiate operation, the contouring mode con-
trol program tape is entered, and quantities defining the desired
contour interval, plotting boundaries, and output scale are entered
from the viewer panel.
Automatic plotting may be ínitiated at any desired elevation.
Plotting proceeds automatically along a contour line until the
contour closes upon itself or intercepts a model or photo boundary.
When one of these occurrences is detected by the computer, the
plotting stylus is raised and the model elevation is automatically
adjusted to the next contour elevation value. The plotting stylus
is then lowered and plotting is resumed.
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