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4. Examples

Example 1

Two vertical control points appear on adjacent aerial photographs. Photography flying height is unknown although it is needed for later computations. The elevation and and x coordinate on each photo for the points are:

Point Elev (ft)  x (mm)  x' (mm) 
T34  882.53  60.922  -35.909 
M60  849.93  29.538  -66.379 




 Determine the flying height.


Compute parallax for both points

Re-arrange Equation E-8 to solve flying height


H = 4.30x103 ft

Example 2

A telecommunication tower appears on overlapping photographs. Coordinates of its top and bottom are:

  Left  Right 
Point x, mm y, mm x, mm y, mm
Bottom 23.84 -15.61 -12.41 -15.62
Top  29.75 -47.85 -18.23 47.89

 The terrain is generally flat and elevation at the tower base 1125 ft. The flying height was 3550 ft and camera focal length 152.44 mm. What is the tower height?


Compute parallax for tower top and bottom

Use Equation E-7 but don't add the tower's base elevation.

Elev = 590 ft