shown there are considerable variations of the geometrical quality of the 
image coordinates within different zones around the center point. Radial 
distortion is most easily determined from the scale variations. 
The method of least squares is strongly recommended for the computations 
in connection with camera calibration, not only because it usually leads to 
the simplest computation but also because well defined information about the 
basic geometrical quality and the error propagation can be expressed in 
arbitrary functions of the image coordinates. 
It is highly desirable that cameras of different focal lengths be calibrated in 
the manner indicated and that the basic geometrical quality be uniquely 
determined from repeated series of tests. The work which is being performed 
in this respect, as indicated by Schmid 1961 and Rosenfield 1961, is of the 
greatest interest. Finally, tolerances can be constructed in various respects.