REPORT OF COMMISSION V GV-15 
Over three approximations are seldom required. These values of f, ZAx and 
EAy are employed in all other exposures. The value of ZAz is a direct measure 
of the accuracy of the focal plane setting, while ZAx and ZAy are a measure of 
the accuracy with which the principal point was made to coincide with the 
fiducial axes intersection. 
2. Procedure for Cones of Less Than 10 Degrees. The spatial resection method 
of determining camera calibration data described in the previous section fails 
when the spatial resection angles are very small. Small cone angles of 5 degrees 
or less yield extremely small resection angles which in turn produce large 
computational errors in the coordinates of the principal point. Fortunately, the 
precise location of the principal point is not significant for small cone angles. 
For this reason, a method of modified dependencies is introduced for the 
determination of focal length only. The method of modified dependencies treats 
the given coordinates of the principal point as correct. 
'The simultaneous equations are developed from the three general forms: 
a form 
COS 04 COS a; + cos f, cos a, 4- COS y1€08 a; — COS ay, 
COS ag COS az + COS B2 COS ai, + COS ya COS a; = COS a, 
COS 3 COS Œ7 + COS B3 COS ay + COS y3 COS a; = COS As; 
B form 
COS a4 COS B , + cos By cos By, + cos yı Cos B, = COS Ba, 
COS a; COS B; + cos B2 cos B, + cos yı Cos B. = cos Bq, 
COS a3 cos 8, + cos B3 cos B, + cos ys cos B; — cos D,, 
y form 
COS a COS y, + COS B1 COS y, + COS Y1 COS Y; = COS Ys, 
COS A2 COS Y7 + COS B2 COS Y, + COS y» COS y; — COS "ys, 
COS 0/3 COS "y ; + COS fs cos y, 4- COS ys COS y; — COS vy, 
where 
VR 
cos an = - E = 
(2,2 + 45)? 
Voi 
cos Bn = 
. 0 2 12172 
(1,2 -- 3, Jd fU 
f 
COS y, — - ; €— 
( Xn” + yn zt £2) di 
cos as, = sin GHA, cos 0, 
cos 8, = cos GHA, cos à, 
COS y,, — Sin 0, 
Division of each equation by cos y, gives a modified form: