3. PREPARATIONS FOR THE CORRELATION PROCEDURE AND THE ACCURACY CONTROL
3.1 General remarks
The correlation program needs informations about the interior, relative
and absolute orientation, which have to be determined in advance. These
values are calculated using conventional analytical procedures. This
limits the effect of exteriour influences and assures in the present
stage of the correlation technique better pre-conditions instead of
doing everything pure digitally.
Additionally in the actual example of small scale pictures some special
effort has to be made for transformations of the available control
information to meet the conventional relations of photogrammetric coor-
dinate systems.
3.2 Interior orientation
The first step encorporates the calculation of the relationship between
digital and image coordinate system. This is accomplished by the mea-
surement of identical image points in either systems. The coordinates in
the analog pictures are measured in a comparator, while for the digital
images a graphic display is necessary.
The discretization effect in the digital pictures which produces prob-
lems in the identification of identical points, together with the preci-
sion of the positional readings which is limited to one picture element
(pixel) makes it indispensable to take several points well distributed
over the image area. This reduces the effect of the mentioned influences
and assures a reliable transformation from analog to digital and vice
versa.
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RESTKLRFFUNGEN RN BILOPUNKTEN
BILD 887 ; TRANSFORMATION: POLYNOM
QUADRATISCHER MITTELWERT (MIKROMETER) 26.2
: LRENGENEINHEIT DES PUNKTFELOES (1 MILLIMETER)
—— — LRENGENE INHEIT DER VEKTOREN (100 MIKROMETER)
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Figure 1: Residuals at control points
For picture 887 the results of the transformation are listed in table 1
and plotted in figure 1. As the plot shows, the remaining residuals are
of random characteristic and caused by the different resolutions. Consi-
dering the invariant results for the two transformations ascertains the
stable geometry of the digital picture.
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