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corrections are:— 
~2 
vx = —dx, — X dz, + ydk (1 + m hd + x do—dx (5) 
h h? h 
2 
m —dya— T dn —Xd«e — eg (1 +3 hdw — dy 
vy = —dyo — 7 deg — xde — D db x ) © 
If superfluous observations are present, the differentials must be determined 
so that the square sum of the residuals v is a minimum or: 
E ve | + |» | = minimum. 
If the points are located symmetrically around the principal point of the 
projector, the normal equations which arise from the minimum condition, can 
be solved in a general way. We assume that twenty-five points are chosen in the 
grid according to Fig. 2. 
The location of a point i is given by y’, x’, The upper left corner is, for 
instance, called the point 51. If the size of the grid is 2a the co-ordinates 
x' y' of the points are as shown in Table 1. 
  
TABLE 1 
Point | x! y