The differences for each distance to the reference 
system are calculate by 
M eod ^ Stereo (26a) 
Ags = 5 5, 
Agl 7 EM i ue (26b) 
Ags is the difference between geodetic distances and 
distances calculated by stereo measurements. Ag is the 
difference between geodetic distances and distances 
calculated by line photogrammetry. The horizontal 
distances based on the geodetic measurements are as- 
sumed to be "true". The empirical standard deviation 
of the distances are 
(A2) 
SAN Lu Q7) 
The number of horizontal lines is denoted n and not 
(n-1) because of the assumption that the geodetic 
distances are "true" values. 
The horizontal lines of the two buildings are pairwise 
perpendicular to each other. Therefore always two EPI 
angles for a image pair exist and are used. Figure 7 
shows o4 for different angle combinations. The angle 
combinations 10/91, 17/84 gon for building A without 
constraint and the combination 15/83 gon for building 
B are about two to three times larger as the other ones. 
A check of the "all"-column shows, that the use of 
more than two images only result in decreased 
standard deviations, if angle EPI is less than about 25 
gon compared to image pairs. Otherwise the calculated 
empirical standard deviations are the same. 
The results based on stereo measurements are presen- 
ted in figure 8. For building A, they are about twice as 
large as those using line photogrammetry with 
constraints. The standard deviations for building B 
have about the same size for both methods, i.e. +7 cm. 
Height differences of the corner points The roofs of 
the two test buildings are horizontal, this is proofed 
with the help of the geodetic method. The mean 
heights are calculated by using the heights of all corner 
points for each of the two buildings. This is done for 
stereo and line photogrammetry. The empirical stan- 
dard deviation of the height of the corner points is cal- 
culated as following: 
AN! 
GA = n-1 5) 
674 
where n is the number of the corner points, Zis the 
mean height and Z; the height of point i. 
For building A the influence of angle EPI on the 
standard deviation of the height differences is only 
detectable, if no geometric constraint is introduced 
Figure 9a. For the angle combinations 10/91 gon and 
17/84 gon the standard deviations without constraints 
are more than three times as large as those with 
introduced constraint. Otherwise the standard devia- 
tions for small angles is less than for those with large 
angles and for them using all images. Figure 10a 
shows, that all results from the stereo measurement, 
with the exception of model 1/2 shows a larger empiri- 
cal standard deviation compared to those calculated by 
line photogrammetry. 
The empirical standard deviations calculated using 
line photogrammetry for building B, in figure 9b, are 
less dependent of the angle EPI compared to the same 
values for building A. Comparing the results from line 
photogrammetry (figure 9b) with stereo photogram- 
metry, shown in figure 10b, are almost the same. In 
figures 8, 10 the column underlined with "mean" is a 
mean value calculated by using all results from the 
stereo measurements. 
5. DISCUSSION 
All tests were based on real data. The results are there- 
fore influenced by several different kinds of errors. 
Nevertheless clear tendences in respect to the varia- 
tions of the angle EPI are shown. This is also valid for 
the introduction of geometric constraints, when image 
pairs, as well as multi images are used. 
The check of the plotted logarithmic functions, in 
figures 5 and 6, shows that it is not possible to establish 
a general relation, which could predict the change of 
the standard deviations in respect to a variation of 
angle EPI, with an acceptable fidelity. The standard 
deviations of the parameters 6, $, y become conside- 
rably smaller, if geometric constraints are introduced 
and angle EPI is less than about 25 gon, this is visible 
in figures 5. The same is valid for the standard 
deviations of the differences of horizontal distances 
( figures 7 ). This allows the inference, that the intro- 
duction of a horizontal constraint causes an improve- 
ment of the estimated planimetric position of a 
straight line. This is not valid for the height values. 
The precision of the Z-component increases strongly, if 
the angle EPI is less than about 25 gon. This is 
estimable when calling in mind that a 3D straight line 
cannot be estimated if it lies parallel to the connection 
of the two projection centers, i.e. when the epipolar 
angle is zero. This is also a reason, that the planimetric 
position is more robust as the height values with 
respect to a small angle EPI. 
The results achieved by line photogrammetry are 
more precise as those from stereo photogrammetry, if 
the angle EPI is larger than about 25 gon, or if the 
measurements from all images are used. The validity 
of this statement is not so strong, as it is only based on 
a small amount of data. More extensive tests are 
needed to achieve a more reliable result. 
We expect, that the introduction of intersection con- 
straints into the adjustment process will result in 
more 
m n 1 Re pw MM