470 
Perspective center 
When measuring the coordinates of the fiducial marks the exact 
location of H' is unknown and the measurements are refered to a 
system (x')> (y') with origin in the point of intersection of the two 
lines connecting opposite fiducial marks and with the (y')-axes as the 
projected image of the y'-axes. As <o is the primary rotation the coordi 
nates of H' are 
tarup 
O') H'= —c —— , (/) H '= c tanw 
LUbCO 
Therefore: 
O') =*'— 0')h' » O') = / + O') if 
When measuring the fiducial marks the image coordinate system 
may be translated and rotated in the system of the measuring instru 
ment X, Y. Accordingly 
X — A 0 + OO cosa — (y') sina 
Y = Y 0 + (x*) sina + {y'i cosa