850 
For calculations of the angle of slope (a) in across flight direction for stereo 
imagery with the same scan direction we can use the following formula (fig. 8): 
tga LI + htg 0 1 
tg a = LI - htg 0 1 
for slopes dipping towards the flightline 
for slopes dipping away from the flightline 
in which LI is the slope length on the image with the smallest depression angle 
0 and h is the height difference between top and bottom of the slope. 
Fig. 8 
Slope measurement (a) for a topographic slope 
scanned from the same 
direction 
Substituting h from equation (6): 
and 
tga 
4p 
Litg e 2 - Litg0 1 + APtg e 1 
for slopes dipping towards (8) 
the flightline 
tga 
Ap 
Litg e 2 - Litg 0 1 - APtg 
for slopes dipping away 
from the flightline 
(9) 
In a similar way the slope can be found in stereo 
(fig. 9): 
h 
L2 - htg 0 ^ 
images with opposite scan direction 
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