Module 3 : Photogrammetry
  Lecture 19 : Geometry of tilted photographs
Ground co-ordinates on tilted photograph
  • Referring to figure 1, the coordinates can be derived by assuming the following situation:
    1. Y-co-ordinate axis lies in the principal plane.
    2. X-co-ordinate axis passes through ground nadir point.

Therefore, ground nadir point is the origin of co-ordinates

wp = x', WP = X

Therefore, scale relationship between plane kwp and KWP is given by

X, Y              Ground co-ordinates
x', y'             Co-ordinate of point with respect to axes whose origin is at the nadir point and whose y' axis            
                      coincides with the principal line
t                      tilt

Flying height for tilted photo
  • The flying height can be derived in a similar as that for the vertical photograph explained earlier. The procedure is given below:
  1. Get photo-coordinates of the end points of control line with respect to axes defined by the collimation marks.
  2. Photographic length of line is scaled directly.
  3. Use ratio of photographic length to known ground length to get first approximation as

where,
f            - focal length
h AB      - Avg. elevation of A and B
AB
       - ground length.
ab       
- scaled photo length.

By using Happ, together with other scale data, one can solve the following equations

4.  Calculate distance based on first set of ground co-ordinates.
5. Compare this computed distance for better approximation of H. Where H is new value of flying height, AB is the value of length based on first approximation height

6. Repeat the procedure till computed value of length agrees with the known ground length within the desired precision