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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