Fig. 3: Geometrical method to find the interior orientation 
3.2 Pairs of Perpendicular Vectors 
As descriptive geometry uses line information, this methods cannot 
directly be used in analytical photogrammetry. Therefore the problem 
has to be verified in a matrix and vector notation. 
Vanishing points are defined as intersections of parallel object lines 
in the image plane. A pair of parallel vectors has to be photographed 
to be able to calculate one vanishing point (Fig. 4). If three 
perpendicular pairs of vectors are available, all requirements of 3.1 
are met, and the interior orientation is fixed. 
  
  
  
Fig. 4: Determination of the vanishing point F' 
3.3 Calculation of the Interior Orientation 
It is assumed that two pairs of perpendicular vectors are known in one 
image. First the parallel vectors vi, Vi and the connection vectors 
(a; -.- a, ) from the projection center to the image points are 
regarded (Fig. 5). 
- 533 =