5, ACCURACY CONTROL OF THE CORRELATED HEIGHTS 
5.1 Control procedure 
For a detailed control of the correlation results two main aspects have 
to be considered, First, to achieve a valuable information about the 
really attained accuracy all these heights the correlation procedure has 
marked as questionable have to be rejected, and second, the comparision 
of the results with the reference DTM should be accomplished in separate 
classes to reflect the influence of the object content. 
The correlation procedure provides three informations to mark a height 
determination as doubtful. The correlation coefficient, the y-parallax 
and the difference to a second height determination. With an appropriate 
selection procedure for the last two criterions /Boochs 1984a/ it is 
possible to distinguish between reliable and less reliable heights, 
while for the correlation coefficient itself the minimum of r=0.6 serves 
as separator between good and bad calculations. 
To differentiate in the results for the influence of the object content 
three major categories have been established : 
- contrast : Depending on the image contrast exteriour influen- 
ces like noise, for example are of more or less 
importance. Therefore it is interesting to evaluate 
if this is reflected in the accuracy. 
- geometry : The complexity of the object geometry fixes if the 
correlation procedure will be able to approximate 
the object surface or if greater deviation during 
adaption to the surface are to expect, what should 
affect the accuracy too. 
- object type : The object type comprises the above mentioned 
influences with some additional characteristics like 
edges, for example. However, for small scale images 
this has to be expected as of minor importance. 
The following subclasses are established for the above categories : 
- contrast : without affection (WA), hazy (HY), elody (CD) 
- geometry : no or low eurvature (LC), steep hills (SH) 
- object type : fields (FD), forests (FO), build-up area (BA) 
The class (SH) comprises surface regions with a slope of more than 100%. 
For the examination of the correlation results each point in the test 
sites was given a value of the above type for each category. These 
values then served for the classification in the control procedure, so 
that only points with the desired characteristics were examinated. 
The judgement of the accuracy is based on the values of the average 
height difference (AZ) and the mean square residuals (mary), which are 
calculated comparing the correlated and the corresponding reference 
heights. 
5.2 Attained accuracy 
Table U4 shows the results of the control procedure. 
Examinating the values for mary in test site Deggendorf it first has to 
be stated that the object type is of major influence for the quality of 
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