2. THE PHOTOGRAMMETRIC MATHEMATICAL
MODEL
The basic mathematical model used to pass from a twodimensional
system (photo) to a three-dimensional system
(object), can be represented by means of the following 3
equations:
Where:
• ξ
0
,η0
 are the image coordinates of the perspective centre
(Principal Point) with respect to the image plane;
• c is the focal length;
• m is the image scale factor;
• rij
 are the elements of the rotation matrix and are function of
angles ω ϕ κ which describe the position of the camera in
the ground-based reference system;
• Xi
,Yi
,Zi
 indicate the absolute coordinates of a generic point;
• X0
,Y0
,Z0
 are the absolute coordinates of the perspective
centre;
It is possible to eliminate the scale factor, that can be not uniform within the photo, by dividing the first and second
equations of the system (1) with the third one: