International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
(b)
Figure 7: Point clouds resulting after the removal of the
vegetation through the morphological filter. LMS-
Z620 dataset (a), VZ-400 dataset (b).
5. CONCLUSIONS
Achieved results show that for both datasets, the iterative and
the morphological filters perform quite well for eliminating
the vegetation, though some manual editing is still required
since vegetation does not feature a prevalent growing
direction. Furthermore, the comparison between the number
of the laser returns left in the final DTMs shows that the VZ-
400 provided a one order of magnitude denser point cloud
wrt. the LMS-Z620. This demonstrates that a TLS with multi-
target capability can potentially provide a more detailed
DTM even in presence of very dense vegetation, as in the
case of the Brustolé landslide area. The use of the calibrated
reflectance revealed to be quite effective to reduce the
number of off-ground points in the pre-filtering stage.
However the selection of the more suited threshold values
was quite difficult as it was based on empirical and manual
methods. This applies overall in the case of the last echoes
where the attenuation effect of preceding targets makes the
calibrated reflectance values of that echoes still range
dependent, so that ground and off-graound points tend to
assume more similar reflectance values. It is authors opinion
that in order to improve the potential of this additional
information for object classification more sophisticated
analysis tools should be developed.
ACKNOWLEDGEMENTS
Authors wish to thank prof. Gabriele Bitelli and his research
team of the Department of Civil, Environmental and
Materials Engineering (DICAM) of the University of
516
Bologna (Italy) for the provision of the Riegl VZ-400 laser
scanner and the technical support given during the survey.
REFERENCES
Axelsson, P., 1999. Processing of laser scanner data
algorithms and applications. In: ISPRS Journal of
Photogrammetry & Remote Sensing, vol. 54, pp. 138-147.
Bitelli, G., Gatta, G., Landuzzi, A., Vittuari, L., Zanutta, A.,
2009. La fotogrammetria digitale di archivio per lo studio
multitemporale di un'area in frana nelle Prealpi vicentine. In:
Proceedings of the 13" Italian National Conference ASITA,
Bari, Italy.
Doneus, M., Pfennigbauer, M., Studnicka, N., Ullrich, A.,
2009. Terrestrial waveform laser scanning for documentation
of cultural heritage. In: Proceedings of the XXII" CIPA
Symposium, Kyoto, Japan.
Haralick, R.M., Shapiro, L.G., 1992. Computer and Robot
Vision. Addison-Wesley, Longman Publishing Co. Inc.,
Boston, MA, USA.
Kraus, K., Pfeifer, N., 2001. Advanced DTM generation from
LiDAR data. In: The International Archives of
Photogrammetry and Remote Sensing, 34(3/W4) , pp. 23-30.
Maas, H.G., 2010. Foresty Applications. In: Airborne and
terrestrial laser scanning. Vosselman, G., Maas, H.G. Eds.,
Whittles Publishing, UK.
Pirotti, F., Guarnieri, A, Vettore, A., 2011. Vegetation
Characteristics Using Multi-Return Terrestrial Laser
Scanner. In: Laser Scanning 2011, 7th ISPRS Workshop,
Calgary, Canada, 29-31 August 2011.
Roncat, A., Wagner, W., Melzer, T., Ullrich, A., 2008. Echo
detection and localization in full-waveform airborne laser
scanner data using the averaged square difference function
estimator. In: The Photogrammetric Journal of Finland, 21
(1), pp. 62-75.
Roncat, A., Bergauer, G., Pfeifer, N., 2011. B-spline
deconvolution for differential ^ target ^ cross-section
determination in full-waveform laser scanning data. In:
ISPRS Journal of Photogrammetry and Remote Sensing, vol.
66, pp. 418-428.
Ullrich, A., Reichert, R., 2005. High resolution laser scanner
with waveform digitization for subsequent full waveform
analysis. In: SPIE Laser Radar Technology and Applications
X, Orlando, Florida, USA, pp. 82-88.
Ullrich, A., Pfennigbauer, M., 2011. Echo digitization and
waveform analysis in airborne and terrestrial laser scanning.
In: Photogrammetric Week 2011, Dieter Fritsch Ed,
Stuttgart, Germany
Wagner, W., Ullrich, A., Ducic, V., Melzer, T., Studnicka,
N., 2006. Gaussian decomposition and calibration of a novel
small-footprint full-waveform digitising airborne laser
scanner. In: /SPRS Journal of Photogrammetry and Remote
Sensing, 60 (2), pp. 100-112.
