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Michael Cramer
3.4.1 Variable image overlap. To check
the influence of variable image overlap on Version Im Check- RMS Object Coordinates [om]
the resulting object point accuracy, the ges. lL pois East North | Vertical
GPS/inertial trajectory calculated from the 1 cross 12 142 7.3 9.0 26.7
25km distance baseline solution was used. 2 Cross 72 142 5.0 7.0 12.1
The achieved accuracy (RMS) in object 3 Cross 36 133 9.0 8.2 15.0
space from check point analysis is given in 4 parallel 15 126 14.3 10.3 23.4
Table 4. Several different versions are 5 parallel 14 138 8.8 11.9 17.8
calculated to investigate the influence of 6 single 7 84 15.0 13.9 23.9
multiple image rays used for the point 7 single 7 95 71 16.1 252
determination. In Version ] all 72 images 8 single 7 92 9.9 211 24.9
(two blocks flown in cross pattern) with up
to 22-30 folded points were considered. The Table 4, Accuracy of direct georeferencing using varying block
intersection for object point determination configurations (GPS/inertial results from 25km baseline)
‘was done using the interior camera
orientation parameters from lab calibration. Analyzing the obtained differences from the reference check point
coordinates the horizontal accuracy is in the 1dm level, but the vertical component is worse due to a significant shift in
the vertical Z-axis. The size of this systematic offset is about 25cm which corresponds more or less to the 30cm offset
in the vertical coordinates of the perspective centre detected earlier (Table 3). Again, the incorrect assumption on the
camera focal length is directly propagated into the accuracy of object point determination. The accuracy in the vertical
component significantly improves applying the corrected interior orientation parameters for object point determination.
Now, the accuracy in height is about 12cm (RMS) and the maximum deviations did not exceed 40cm in all coordinates
(Version 2). For the east/north components the RMS values are well below 10cm. To further re-confirm the results of
direct georeferencing only one single 1:13000 image block is processed separately (Version 3). From 36 images and
133 re-computed check points similar RMS values for the horizontal and vertical accuracy are obtained, although the
image overlap was reduced by a factor of two. Nevertheless, the maximum deviations are bigger than before. This is
due to the fact, that only 15-folded image points (max.) could be used for point determination. To simulate the standard
photogrammetric data situation (photogrammetric block consisting of several parallel strips with standard 60% / 30%
image overlap) the number of images is further reduced. In Version 4 only three north-south strips, in Version 5 only
two east-west strips are used for point determination. Using standard block geometry the maximum number of image
overlap is reduced to six which again deteriorates the obtained accuracy. Now, the horizontal accuracy is within 10-
15cm, the vertical accuracy about 20cm which shows the positive effect on high image overlap and strong block
geometry. This effect becomes more clearly when single image strips are considered where 2-3 image rays are available
for intersection only (Versions 6-8). As mentioned before this scenario is quite interesting for the surveying of linear
objects like power lines or traffic routes. The maximum deviations rise up to 30-90cm and the RMS values are
deteriorated up to 20cm in X, Y and 25cm in height, consequently. Again, the reduced number of image rays influences
the object point accuracy. Additonally, since the misalignment angles are estimated from all 72 images of the 1:13000
scale and not from the images considered in the different versions only, remaining systematic errors are present in the
exterior orientations. Besides the influence of uncorrected distortions in the imagery, these misalignment errors will
cause some portion of the errors budget for direct georeferencing in object space. Considering e.g. the single flight line
(Version 7), the difference between the optimal misalignment angles calibrated from all images and from only 7 images
within this strip reaches about 1.2: 10?deg and 1.510?deg forthe - and -angle. This will introduce significant shifts in
object space of about 5cm from a flying height of 2000m above ground.
3.4.2 Variable baseline length. A special
feature of this test flight are the different Block GPS/inertial RMS Object Coordinates [cm]
GPS/inertial trajectories obtained from multiple solution East North Vertical
base stations in varying distances to the test site. ; S..25km 14.3 10.3 23.4
Since the baseline length is of major interest for = = a F 720km 13.4 9.9 19.7
photogrammetric applications, where the distance 2 92| B 230km 13.3 10.3 20.1
iim eser Sud rover eric might be NY en H 350 m 13.9 10.3 20.9
ong especially in remote areas, e :
georeferencing was repeated using the orientation $32 ; cr d d Bs
data from the four GPS/inertial trajectory S e E = 10 18.0
solutions mentioned before. To simulate standard Qu B 230km 172 14. :
photogrammetric conditions the investigations H 380 km 11.3 15.0 24.6
were done using sub blocks consisting of parallel Table 5, Accuracy of direct georeferencing using varying baseline
strips with standard overlap again. Three north- length (standard photogrammetric overlap conditions)
south strips and two east-west strips with 15 and
14 images and 131 and 126 check points were
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 203
