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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
Data processing stage has followed data acquisition to provide a
cartographic representation of collected data, to support quarry
management and to allow geological analysis.
Laser data and digital image have been processed using the
Reconstructor software developed by the Joint European
Commission Centre (Sequeira V. et al.,1999) according to the
following steps:
l. range scans pre-processing, editing, geo-reference,
meshing and texturing;
2. geometrical information extraction (cross-sections,
surface measures, iso-lines) and DSM generation;
3. geological analyses.
Pre-processing is performed immediately after data capture and
includes /ocal surface normal computation. This information is
a very valuable support for next geological analyses.
A fully GCP-based registration method has been adopted. The
software allows also a feature-based registration (ICP method)
which could be useful for comparison with future acquisitions.
Starting from the actual survey which can be chosen as
reference and registering to it all the other range scans, it will
be possible to verify quarry temporal changes. Reconstructor
provides tools to build 3-D models and perform automatic
comparison between models built at different time of the quarry
life.
An intelligent data reduction is provided through a multi-
resolution meshing process which converts the set of the raw
3D points into a continuous surface. The Reconstructor
software allows mapping external 2D images on the 3D mesh;
color information enriches geometrical information helping the
geological data interpretation.
The data processing creates a texture-mapped 3D model of
quarry containing the complete geometric 3D and 2D
information. The software becomes a virtual surveying tool,
which extracts the information from 3D and 2D surveyed data
and hands it over to standard software for cartographic
representation and DEM generation.
Major results of the marbel quarry laser survey campaign have
been: point and distance measurements, area and volume
measurements, interactive and automatic fitting of planes,
creation of cross-sections, DEM generation, iso-lines
cartographic representation (see Figure 5).
This dataset of results and products constitutes a valid support
for geological and geo-mechanical analyses of the excavation
area, requiring both geometric and colorimetric data.
Figure 5: Processed range scans used for geological analysis:
different colors correspond to different quarry slopes
713
4. FINAL DISCUSSION
In the paper some technical aspects of the application. of
terrestrial laser scanning to survey site of interest by geological
purpose have been presented. The current availability of long
range TLS becomes possible the operational use of this survey
tool, which may provide products that cannot be obtained by
other topographic and photogrammetrye methods, or can be
obtained with a largely minor effort and consumed time.
Two tests leaded by the research groups of the authors have
permitted to have a look on practical methods, solutions and
problems as well. Within the main advantages of laser survey
applied to geology, the following can be listed: fast data
acquisition due to remote data collection (direct survey of 100
m? surface can require around 2 hours to an expert operator);
completeness with respect to traditional survey using "spot"
data acquisitions (1 local spot survey every | kn; increased
measurement accuracy (e.g. in traditional geological survey,
local compass measurements are still collected to establish
attitude of discontinuities).
Further developments either in algorithms and procedure for
registration, and in application and operational aspects have to
be carried out in the near future. A laser scanning survey results
in several hundreds of Mb data, which are still difficult to be
managed by commercial softwares and common PC.
Optimization of processing and visualization tools is needed,
while techniques to optimize the survey planning in order to
reduce the size of point-clouds from the acquisition stage are
expected.
ACNOWLEDGEMENTS
We would like to thank Simone Orlandini (MicroGeo, Firenze,
Italy) and Riegl company (Horn, Austria) for having provided
TLS instruments used in both experimental tests.
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