Step 1. Approximate Triangulation. Using available projective parameters, one 
employs the measured plate coordinates to triangulate approximate coordinates 
X,Y,Z of the photographed point. From these and the coordinates X^, Y^, Z^ of 
the exposure station the approximate distance s' to the object plane containing the 
photographed point can be computed from 
1 
!o- [2€ + (Y-YOP + (Z-20)21° cos 8, 
cos 8. = c/lc® +12), 
in which r is the radial distance of the image and c is the principal distance of the 
camera. 
Step 2. Computation of Distortion Coefficients for Object Plane at s'. With s' 
provisionally determined by approximate triangulation, one evaluates the parameter 
where s, and s, correspond to the two object planes for which distortion functions 
have been calibrated. The coefficients corresponding to the object plane at 
distance s' are then evaluated from 
Step 3. Evaluation and Application of Distortion Corrections. From the known 
distance s of the object plane focussed on and the approximated distance s' of the 
object plane containing the photographed point one evaluates the parameter 
e! 
s '