CONTROLS
Controls for operating the Automated Planimat are mount-
ed in the control box to the left of the operator. Four mode se-
lection pushbuttons are provided, enabling the following modes
of operation: standby-manual, orientation, manual check, and
automatic.
A momentary pushbutton is provided to enable connec-
tion of the correlation loop to clear x parallax during the orien-
tation procedure. A switch is provided to raise or lower the
profile recording stylus in the SG-1 storage unit. This switch
provides a manual override for the stylus which is normally
raised and lowered automatically in automatic operation. Indi-
cator lights are provided on the control box to monitor opera-
tion of the equipment. In addition to the above, controls nor-
mally associated with the Planimat such as the start pushbutton,
the y-y! lever, the reset switch, and the y speed control potenti-
ometer are also mounted on the control box. Setting up adjust-
ments for pointing and centering the cathode-ray tube scanning
patterns are also contained in the control box. These controls
are preset and are used infrequently in normal operation.
CORRELATOR PERFORMANCE FACTORS
To accurately clear x parallaxes, the correlation system
must accommodate the x scale and x skew distortions produced
by terrain slope, and the y scale and y skew distortions produced
by aircraft roll and pitch.
x scale distortion is produced by terrain sloped in the x
direction and is given by
dx, — 1-(X/H) dHJdx
dx, 1-(X|H - BIH) dH|dX
where dH/dX is the tangent of the terrain slope in the x direc-
tion. The maximum relative scale ratios occur for slopes at the
midpoint of the base and for acquisition systems giving the
largest base to height ratio, B/H. The largest base to height
1
ratio for vertical photography is found in super wide angle sys-
tems. Using B/H = 1, we obtain
dx, 1-0.5 dH/dx
dx, 1+0.5dH|dx
A plot of this equation is shown in Fig. 8.
x skew distortion is produced by terrain slopes in the y
direction, and is given by
dxy (X/H) dH/dY
dy 1-(Y/H)dH[dY
where dH/dY is the tangent of the terrain slope in the y
direction. A plot of this equation is shown in Fig. 9, for
Y/H = 1.3.
An analysis of the y distortions produced by roll and
pitch angle of up to +5 degrees showed that the worst case
occurred when the left and right photographs were obtained
with the vehicle rolled and pitched 5 degrees in opposite direc-
tions, producing a y scale error of 1.4 and a skew angle of
10 degrees.
To determine the distribution of terrain slopes likely to
be found in practice, an analysis was made of 1:24,000 map
sheets covering rugged terrain, broken into l-inch-square sam-
pling areas. The maximum. slope in each sample area was deter-
mined and the results are shown in Fig. 10. The most frequent
slope was between 20 and 25 degrees, and no slopes in excess
of 35 degrees were found.
The maximum slope of 35 degrees was then applied to
Figs. 8 and 9, from which it was found that the maximum x
scale ratio was 2:1 between left and right photographs, and the
maximum x skew angle was 76 degrees between photographs.
