to planimetric offsets at the ground as follows. Roll and pitch at
nadir: 44cm; yaw at image corner: 1.3m; Z at image corner:
1.1m.
These results concerning the position (of the ‘projection center’)
are, in general, in line with those given in Sec. 1.1. Compared to
(EisenbeiB, 2009) and (Eisenbeif et al, 2009) the here presented
results for the planimetric positioning are a bit worse, but gener-
ally the sample for comparison is small. It is therefore difficult to
attribute those differences either to the method of trajectory com-
putation or the method of comparison. Like in (Haala et al., 2011)
the expected accuracy derived from the antenna/receiver specifi-
cation was reached for positioning. These papers, however, do
not consider the estimation of the angular attitude, as it was done
in this contribution. Compared to (Eugster and Nebiker, 2008)
our real world examples based on standard low cost sensors con-
firm their a-priori estimation of angular accuracy and their influ-
ence of ground points.
While these values might already be sufficient for certain map-
ping tasks, the observations used for direct georeferencing can be
utilised in an integrated georeferencing of the acquired imagery.
Without additional costs or equipment, the presented approach
can considerably narrow down the search space in automatic im-
age orientation and might support a bundle adjustment in the case
of a significant amount of gross errors (e.g. mismatched tie points
due to bad image texture). As (Haala et al., 2011) point out, ‘ver-
tical images’ with deviations of the viewing axis from the nadir
in the order of 30° may occur for light weight UAVs.
It will further be investigated if the constant values for the “mount-
ing calibration” can be verified. This would open up the estima-
tion of these offset parameters on a small set of control points in
the immediate vicinity of the take-off/landing site. As no ref-
erences to angular accuracy of direct geo-referencing of light
weight UAVs with on board sensors was found, the above accu-
racy estimates should be further tested. With respect to applica-
tions geomorphology on the one hand, and ecology on the other
hand (Miicke et al., 2011), will be further explored, because both
can profit form georeferenced vertical close range photogramme-
try for monitoring purposes.
6 ACKNOWLEDGMENTS
The Ludwig Boltzmann Institute for Archaeological Prospection
and Virtual Archaeology (archpro.lbg.ac.at) is based on an inter-
national cooperation of the Ludwig Boltzmann Gesellschaft (A),
the University of Vienna (A), the Vienna University of Technol-
ogy (A), the Austrian Central Institute for Meteorology and Geo-
dynamic (A), the office of the provincial government of Lower
Austria (A), Airborne Technologies GmbH (A), RGZM-Roman-
Germanic Central Museum Mainz (D), RA-Swedish National Her-
itage Board (S), IBM VISTA-University of Birmingham (GB)
and NIKU-Norwegian Institute for Cultural Heritage Research
(N). The work was supported by the TransEcoNet project within
the EU Central Europe program co-financed by the ERDF. This
study was partly undertaken within the EU project NEWFOR,
financed by the European Territorial Cooperation Alpine Space.
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