respectively be selected by the criterions of (18),(23),(24)
or (13).
Discrepancy of the criterions can also be demonstrated in
Fig. 5. Because of the mistake of initial parallax, the tar-
get signal S searchs in the wrong range with signals W and
4. Thus we may get wrong correlation of SW by the algorithm
of sum of squares of differences and of SZ by correlation
Coefficient criterion.
HDD
S w Z
Fig. 5 Wrong correlations
Another example using practical data is shown in Fig.6. The
gross errors of parallaxes resulted from the three criterions
are different,in which the other conditions are keept same.
The gross errors shown in Fig. 6 are the integrated results
of six frequency channels.
n Srerrair Suriace
Gross error from:
x "v
- Cas
- *
Fig. 6 Gross errors from three criterions
The discrepancy of the criterions and the fact of different
matching mistakes arise from a same pair of images by the
use Of different criterions indicate that the applying of
such single criterions in photogrammetric image correlation
is not perfect in theory.
3. MULTIPLE CRITERIONS
Due to the disadvantages of single criterions, we may consi.
der using dual or triplex criterions to enhance the relia-
bility of image correlation. For example in Fig. 5, both the
wrong correlations of SW and SZ may be rejected by applying
the dual criterion formed uvon the sum of Squares of diffe-
rences and correlation coefficient.
Some realizable algorethms are discussed in the following.
(a) The combination of covariance and sum Of absolute dif-
ferences.
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