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Mathematical Definitions 
Physical Definitions 
radial distances when these distances are 
measured, not in the image generated by 
the lens in the survey camera, but in the 
completed photographic negative or posi- 
tive. They accordingly contain the in- 
fluences of all photographic and optical 
processes following exposure (e.g. regular 
film shrinkage, alterations in scale ratio, 
ete.). 
  
Distortion Ar: 
The general function c,.F (r) is often 
referred to the pertinent central projection 
c, tan v: 
Sue. une. 
The deviation A 7” from this central pro- 
jection is termed distortion. It depends 
upon 7 and accordingly upon 7’, and is 
usually stated in microns. 
  
  
  
Image constant c: 
The length of the stretch OH’ from the 
projection center to the principal point. 
In the mathematical ideal case the image 
constant c is identical with the camera 
constant ce, 
The term focal length, in the sense of 
image constant, should be avoided as 
being customary in optical terminology, 
where it has another meaning. 
Camera constant cj: 
The scale factor c, in the above equations 
is termed the camera constant. It has the 
dimension of a length and is usually sta- 
ted in millimeters. The camera constant is 
fixed arbitrarily, but preferably so that 
F (v) departs but slightly from a suitably 
chosen simple function (in most cases 
tan 7). 
It is recommended in the case of 7” = c,. 
.tan 7 + A7/,to fix the camera constant 
in such a way that the radial distance r,' 
is stated for which the distortion is to 
equal zero. From the corresponding object 
angle 7, there follows because of 
A 7 = 0: 
/ 
7:0 
tan 7, 
  
Cx 
7’, is termed the zero distance, and 7, the 
zero angle. r, may be chosen arbitrarily 
but must be stated together with c;. 
The camera constants of the survey ca- 
mera and the plotting camera can be 
termed the survey camera constant c, and 
the plotting camera constant c;. 
Image constant c: 
The scale ratio factor of the image funct- 
ion. In plotting, c is made equal to c.