it is rather difficult to establish the nessecary test fields, because of the required
elevation differences.
In the Grimeton tests reported in [13] the camera constant and the principal
points is determined, but it is nessecary to know the position of the exterior pro
jection center in the co-ordinate system of the test field. The camera is located
in a high tower and the external circumstances are changed artificially (cooling,
filters). As the camera is not in an aeroplane, the test cannot be regarded as
being done under operational conditions.
In some cases there are difficulties to define the exterior projection center
physically. As the position is determined from measurements, there also are
errors introduced.
8.4.1. Proposed Pest Fields.
At Nacka, south-east of Stockholm, there are three rather high broadcasting
antennas in a limited area. Two of them are some 190 m and the third 300 m
high. Suppose we had targets on the antennas and on the surrounding ground
that gave an image as in Fig. 20, then the corresponding weight and correlation
numbers would be those in Table 14. If the standard error of unit weight of the
image co-ordinates is 5 i/m, then the camera constant has a standard error of
7 /<m and the co-ordinates of the principal point has 7 //m and 9 ,«m stan
dard errors respectively. To obtain these values the ground co-ordinates must be
very accurate. If we start by saying, that the standard error of the ground co
ordinates has to be smaller than 1 //m in the scale of the negative, this means
Fig. 20.
Proposed test field in Nacka. The flight direction is chosen so that the antenna points fall in
the corners of the picture.The heights of the antenna points are assumed to be 200 m, 200 m
and 300 m respectively. The flying height 500 m. Wide angle camera. The corresponding
weight and correlation numbers are given in Table 14.
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