International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004
interpolation (figure 8). It is clearly visible that morphological
details are not considered in a sufficient way.
Figure 8: Exemplary comparison of the derived contour lines
from analytical plotter (top) and Image Station
(bottom) for model 223_224, overlaid on their
height difference grid, respectively. Positive height
differences are bright, negative differences dark.
4. CONCLUSIONS AND FUTURE WORK
The investigations accomplished so far have shown, that a fully
automated image processing for aerotriangulation and DTM
generation does not provide results that are as reliable as the
reference data measured on an analytical plotter. Concerning
aerotriangulation, for the Nasca project a feasible solution
would be semi-automated processing using the automated tie
point extraction of a digital photogrammetric workstation
enhanced by manual measurements in areas of weak point
density.
DTM generation can be advanced considerably with digital
photogrammetric ~~ workstations, compared to manual
measurements on analytical plotters. However, the performed
tests show that the terrain characteristics affect the obtainable
accuracy and reliability significantly. Manual measurements and
extensive post editing are required to achieve results which hold
the accuracy level of analytically generated DTMs.
The problematic results do not occur in the flat areas with
homogeneous texture, where perhaps the automatically derived
DTMs are even more accurate than the manually measured
DTM due to their high density of matched points. The large
blunders, which require manual editing, are mainly located on
the steep slopes.
326
Further investigations on an automated processing of Nasca
imagery will be done on an internally developed software
package for DTM extraction. First tests, which produced no
satisfactory results, have shown, that the software still needs to
be improved on aerial imagery. Commercial software packages,
including Virtuozo and Image Station, will be further examined
regarding aerotriangulation and DTM generation. Especially for
Image Station, a direct investigation of the matched points
could possibly lead to better results if external DTM
interpolation software is used.
Another topic is the integration of manually measured
breaklines as pre known data into the matching process for
automatic DTM generation, which could improve the accuracy
in areas containing discontinuities, but would increase the cost
due to the required manual measurements.
ACKNOWLEDGEMENTS
The author would like to thank D. Keller, former ETH Zurich
student, for her dedicated work within the scope of Virtuozo
and analytical plotter measurements and processing, as well as
the students A. Weber and S. Zingg for their aid on image
scanning and measurements on the analytical plotter.
REFERENCES
Baltsavias, E., Kiser, C., 1998. DTM and orthoimage
generation — a thorough analysis and comparison of four digital
photogrammetric systems. In: The International Archives of the
Photogrammetry, Remote Sensing and Spatial Information
Sciences, Stuttgart, Germany, Vol. XXXII, Part 4, pp. 42-51.
Baltsavias, E., Li, H., Gaschen, S., Sinning, M., 1996. DTM
generation with the Leica/Helava DSW 770 and Virtuozo
digital photogrammetric systems. Photogrammetric Systems.
Paper presented at the Symposium Geoinformatics 1996, 16.-
19. October, Wuhan, China, pp. 10-17.
Grün, A. Bir S, Bülrer, TL, 2000. DTMs derived
automatically — Where do we stand? In: Geoinformatics, Vol. 3,
No. 5, July/August 2000, pp. 36-39.
Grün, A., Lambers, K., 2003. The geoglyphs of Nasca: 3D
recording and analysis with modern digital technologies. In:
Acts of the XIVth UISPP Congress, University of Liège.
Belgium, 2-8 September 2001, section 1: theory and methods -
general sessions and posters (BAR International Series 1145),
pp. 95-103.
Keller, D., 2003. Genauigkeitsuntersuchung zur automatischen
Aerotriangulation und DTM-Messung im Projekt Nasca.
Diploma Thesis, unpublished.
Supresoft Inc., 1999. Virtuozo NT User's Manual Version 3.1.
Supresoft Inc., 2002. Virtuozo User's Manual Version 3.3.
Z/l Imaging Corporation, 2002. Image Station Automatic
Elevations Help (4.00).
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