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| Titel |
Simultaneous relative and absolute orientation of point clouds with "TLS radomes" |
| VerfasserIn |
Philipp Glira, Christian Briese, Nicole Kamp, Norbert Pfeifer |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250083975
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| Zusammenfassung |
| For the georeferencing of point clouds acquired by a terrestrial laser scanner (TLS) targets
with known coordinates (control points) can be used. The determination of the
target positions in a global coordinate frame with a total station and/or with GNSS
can be very time-consuming. For multi-temporal comparison of TLS data these
targets can be permanently installed on the measurement site. In permanent changing
environments (e.g. high-moutain proglacial environments) this is not possible due to the
movement of the targets. Furthermore, the integration of the TLS data with other
data sources (e.g. airborne laser scanning data) has to be considered. For that aim
the georeferencing of TLS measurements in a global coordinate frame has to be
established.
This work describes a new method for the simultaneous relative orientiation (registration)
and absolute orientation (georeferencing) of point clouds by using spheres with a GNSS
antenna inside. These spheres are thus used as GNSS antenna radomes. Consequently they
are called within this work "TLS radomes". The simultaneous measurement with at least
three GNSS antennas during the TLS data acquisition leads to long measurement
times, i.e. high position accuracy and subsequently a very accurate realization of the
datum.
The presented TLS radomes consist of two hemispheres of polyethene enclosing the
GNSS antenna. The GNSS antenna is mounted on an antenna rod, which can be enhanced by
a prism and/or a reflective cylinder. For a modified optical reflectivity several coatings were
tested. The one causing the smallest deformations, the smallest noise, and with the highest
reflectivity was chosen. The whole construction can be mounted on a tripod. The TLS
radomes are suitable for a wide range of different TLS sensors (i.e. independent of the
ranging principle and the manufacturers).
For the simultaneous relative and absolute orientation of the point clouds the centers of
the radomes are used as identical points. With TLS these centers can be determined in a
sensor own coordinate system (SOCS) by sphere fitting. With GNSS these centers are
determined in a global coordinate reference frame. The transformation parameters are
estimated within a hybrid least-squares adjustment. Further observations, e.g. measurements
with a total station, can be added to the adjustment to improve the accuracy of the estimated
transformation parameters.
Several tests were carried out to check the influence of the radome on the GNSS antenna.
These tests showed that the radome produces minor phase center eccentricities (1-2 mm) and
phase center variations with amplitudes up to 5 mm. Thus an antenna calibration is needed for
high accuracy requirements. Furthermore the eccentricity of the GNSS antenna in respect to
the sphere center had to be determined.
The application of the TLS radoms is proven on a data set consisting of five TLS scans
and GNSS measurements with a duration of up to four hours acquired at the Gepatschferner
(Tyrol, Austria).
The TLS radomes were developed within the research project PROSA (high-resolution
measurements of morphodynamics in rapidly changing PROglacial Systems of the Alps). |
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