c) The indirect influence of the correction. When the first parenthe
sis of formula (13) has been expanded we obtain the term of
y 2
second degree —
In the denominators of the second parenthesis RH and 2 RH
will predominate. Because of that we obtain the parentheses —
B
R '
From formula (13) we then obtain the term of higher degree:
d) We add the expressions (3), (10 c) and (13 a) and then find
the sum of the terms of higher degree to be zero. We find that
all the elevation-deformations can be compensated by the absolute
orientation.
6. Determination of the distortion-effect from a stereo-model.
Methods have been developed to determine the distortion from ste
reo-models. The result has often been obtained as the sum of all radial
distortions. Se e. g. (1) and (2).
If the distortion is determined from horizontal parallaxes —- eleva
tion differences — the measurements must be corrected for the re
mainders in relative orientation, leading to model-deformations of
higher degree. Sometimes mean values are calculated from the four
quadrants of the stereo-model prior to further calculations. If that is
the case only the cylindrical deformation has to be corrected. That is,
for instance, the case when »The Ice Method» is used. See (3). When
the latter method is used the difference in nadir-direction between the
two pictures in the stereo-model must be taken into consideration.
This has been proved above. A practical application gives the same
result.
In table 1 below different determinations of the influence of the
curvature of the earth have been put togehter. Features common to the
different determinations are that the flying altitude is presumed to be
10 000 metres and the focal length 0.15 meters. The amounts of distor
tion are given in the scale of the negative in the unit mm • 10— 3 . For
all three series dr 6 has been put = 0. The radii are n • 1 000 metres,
measured on the ground.
6 a) The values have been calculated from formula (6).
6 b) The differences in elevation of the earth-surface have been
calculated from formula (3). These elevation-values have been
put into the formulas given in (3), pages 3d—36.
