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7. Requirements on Test Objects 
Using formulas 5.5.5 and 5.5.6 to solve for the parameters of the interior ori 
entation, the location of the points on the test object must be such that the cor 
responding matrix of normal equation coefficients (A’P A in formula 6.1.17) 
is non-singular. The test object must also give a good sample of the bundle of 
rays from the camera. It is impossible to use every ray of the bundle in the test, 
but the sample of them must be taken so that the points are uniformly distri 
buted over the image area. This seems to be a reasonable way of getting infor 
mation from the entire bundle of rays. 
7.1. PLANE TESTS OBJECTS 
It is rather easy to make plane test objects. They can be established on glass 
plates, on walls of buildings, in flat terrain etc. For these test objects all points 
have, or are reduced to, the same (Zj-co-ordinates. If the test plane and the 
image plane are almost parallel we cannot determine both exterior and interior 
projection centers, because we get the following linear dependence among the 
coefficients of the observation equations: 
(Z) 
a x o + ax o — 0 
(Z) 
a u o + aY 0 = 0 
(Z) 
a c — azo = 0 
7.1.1 
7.1.2 
7.1.3 
where (Z) from formula 5.1.5 is constant for all points. This means that some 
thing must be known about the exterior center of projection to give the possibi 
lity of determining the interior orientation, i. e. the co-ordinates X 0 , Y 0 and Z 0 
must be known and their corrections excluded from the adjustment. From for 
mulas 7.1.1, 7.1.2 and 7.1.3 we can derive the influence of errors in the exterior 
projection center upon the interior orientation in the case of vertical photo 
graphy. For the principal point we obtain: