and with a focal length of 150 millimeters, an input scale of
1/20,000 resulted. By using duplicate diapositives tilted
identical amounts (three meters vertically for each 500 meters
horizontally in both x and y) and producing three meter line
drop contours, a value for sensitivity or "C" factor was obtained
which was essentially free from all external errors such as
those contributed by ground control, film distortion, etc. This
value represents the cumulative errors of the UNAMACE itself.
The output was a set of sharply defined bands running at 459,
Measurement and analysis of this output showed an average height
uncertainty of 0.25 meter or an instrument "C" factor sensitivity
of 6,000 for vertical photography of this focal length and scale.
b. Typical of single model tests are the following
two. The first is a model of Gila Butte, Arizona flown at 33,000
feet with a six inch focal length camera, giving an input scale
of 1/66,000. Output scale was 1/62,500 with a 40 foot contour
interval. This area is gradually sloping with approximately
250 feet of relief in one corner. The model was compiled in
one hour. The orthophoto with superimposed contours are shown
in Figure 16. In the terrain shown there were only one or two
stops requiring manual intervention. Based on interpolating
elevations from the extracted contours for 44 spot elevations,
there was a mean error or datum shift of 10 feet and an indicated
"C" factor of approximately 1,500. The second model was of Fort
Sill, Oklahoma and was flown at 25,000 feet with a six inch focal
length camera, giving an input scale of 1/50,000. Output scale
was 1/50,000 with a 40 foot contour interval. This model was
about 400 feet of relief and was compiled in 85 minutes. A "C"
factor of 2,300 with a mean error or datum shift of four feet
was achieved based on interpolating elevations from the extracted
output contours for the 37 ground points. Figures 17 and 18
show this compilation as a contoured orthophotomap and the line
drop output with the contour lines superimposed.
c. Inspection of the line drop output reveals how
the draftsman averages and interprets the dropped lines. The
series of horizontal lines and symbols in the upper left indicate
the boundaries where the "ADV-AR" was employed. The scrambled
dropped lines in this area are over a large body of water where
correlation does not occur. The UNAMACE failed to properly
correlate at the edge of this lake and as a consequence approxi-
mately fifty manual interventions were necessary in this area.
This time is included in the overall compilation time of 85 minutes.
The remainder of the model required no manual intervention.
The drafted contours, grid lines, etc., are overprinted on the
line drop output for comparison purposes. The indicated ''C"
factor is sufficient to compile a 10 foot contour interval, but
in practice this cannot be achíeved because of the line drop
definition at this contour density. A 20 foot contour interval
chart was drawn by shifting the datum by 20 feet, compiling 40
foot contours and combining the two 40 foot contour charts. It
is expected that when contours are compiled from the digital tape
output this problem will no longer exist. This orthophoto, which
is typical of a 1:1 product, represents a resolution of about 40
line pair per millimeter as produced by a hígh contrast USAF type
resolution target placed in the input diapositive holder.
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