4. RESULTS OF THE COMPUTER SIMULATION
By a computer generated model and systematic variations of these para-
meters of the camera and the model their influence on the accuracy of
the DEM was investigated.
Generally the accuracy of the DEM coordinates in the strip axis and at
both borders of the strip were determined only up to the middle of the
strip because of their symmetry. Sometimes the mean square errors
XGEN, YGEN, ZGEN of all single errors have been formed to represent the
accuracy over all points.
Fig. 7 demonstrates the effectiveness of the angular arrangement of the
outer sensor lines in the focal plane. Parallel arranged sensor lines
A and C (a = 0) produce a periodic swing of the X-, Y- and Z-coordi-
nates (in Fig. 7 only the hight errors E are represented).
0; m Highterror of Flight altitude h 4.0 km
the strip axis Strip length 18.6 km
Strip width 3.2 km
e Update point interval 0.2 km
5.0 4 E> Focal length c 100.0 mm
J À Image error 0, + 5.0 um
^ , œ= 0 3
4.0 — l \ ^ X
l \ /
; \ / \
. / m
3.03 | : / i of E
} \ / \ / \, 2457 7
/ \ / X / \ M \
3 UJ , / \ / s
2.0 J \ / A i \ / \
^ \
7 45] \ / \ / \
6 7 \a +4 \ / .
= 10} Ud 7 / d
19 = ca as À ! ET. \ ^ M
I » >
rene © nim Ps d
. Middle of the strip
T T T I b I A: i T
1 2 3 4 5 6 7 8 9 km
Strip coordinate X
+ + L- T }
1 2 3 4 b
Figure 7. DEM-hight errors dependent on the sensor geometry
The length of these periods correspond to the base length b of the
strip. Under certain circumstances these error amplitudes increase up
to a point where the solution of the normal equation is impossible
(Fig. 9).
On the other hand, the arrangement of inclined sensors A and C (for
example a = 109) reduces the amplitudes and the absolute values of the
error curve considerably. Therefore, the angle a between the outer
sensor lines A and C and the center sensor line B is an important
camera parameter with considerable influence on the accuracy of the
DEM coordinates. Even small sensor angles a of a few degrees stabilize
the model remarkably as Fig. 8 demonstrates.
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