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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008 
Figure 10. 3D comparison between laser scanner and image matching of the central area of the marble in Figure 8. The area has been 
modeled with the ETH matcher using three convergent images and then compared in IMInspect with the range data acquired with a 
Surphaser 25HSX laser scanner. The colour-coded differences of (a) Canon and (b) Mamiya show an apparent laser penetration of ca. 
3 mm in both cases. The colour legend on the right shows differences between + 5.5mm and - 5.5mm for Canon and +8mm and - 
8mm for the Mamiya. The Mamiya results are more noisy mainly due to the GSD of 0.6mm, while for Canon the GSD was 0.3mm. 
The black line shows identical regions. 
5. CONCLUSIONS 
In this contribution, we presented the image-based 3D modeling 
of the Erechtheion monument. Data acquisition, processing, 
problems encountered and the results of the digital 
reconstruction have been discussed. Due to the complexity of 
the monument, the relatively large baselines of the images and 
the significant occlusions, primary manual measurements were 
applied to reconstruct the 3D geometry. For some detailed areas, 
automated procedures able to recover dense point clouds were 
instead applied. 
Advanced matching algorithms results have been reported, with 
an accuracy potential similar to that of laser scanning. 
Furthermore, we have shown that marble is a very challenging 
material due to either lack of texture and strongly anisotropic 
reflectance properties. For these reasons, the use of cameras 
with good radiometric quality and low noise, as well as good 
pre-processing are imperative. 
Furthermore, comparison of IBM and laser scanning and the 
apparent penetration of laser pulses into the marble surface 
were investigated. The resulted effect of signal penetration 
seams quite strong (3 mm on the average). This effect needs 
deeper investigations and more tests with different laser ranging 
technologies and light/pattem projection ranging systems must 
be done in this context. 
The lesson of the work reveals once more that a single 
technique is still not enough for the complete and detailed 
modeling of large heritage monuments and sites. The 
combination of different techniques is still the best choice for 
these kinds of projects, exploiting the inherent strength of each 
approach and each one where it is best suited. 
Future work will include the detailed IBM of the Maidens 
porch and of top parts of Erechteion using the balloon images. 
ACKNOWLEDGMENTS 
This work is part of the project “Development of Geographic 
Information Systems at the Acropolis of Athens“, financed by 
the European Union and the Government of Greece, and 
supervised by the Acropolis Restoration Service, Hellenic 
Ministry of Culture. The partners in this project are Elliniki 
Photogrammetriki Ltd (Elpho), Athens, Geotech O.E., Athens, 
ETH (Swiss Federal Institute of Technology), Zurich, National 
Research Council, Canada, Institute for Mediterranean Studies, 
Foundation for Research & Technology (FORTH), Rethymnon, 
Crete, with external cooperators, Leica Geosystems, 
Switzerland and Basis Software Inc., USA. 
REFERENCES 
Allen, P., Troccoli, A., Blaer, P., 2005: Automating the 3D 
Modeling Pipeline, CREST 3D Modeling Symposium, Tokyo. 
Blais, F., 2004: A review of 20 years of Range Sensors 
Development. Journal of Electronic Imaging, 13(1), pp. 231- 
240. 
Blomerus, P., Lesk, A., 2007: Using AutoCAD to Construct a 
4D Block-by-Block Model of the Erechtheion on the Akropolis 
at Athens, I: Modeling the Erechtheion in Four Dimensions. 
CSA Newsletter, Vol. XX(2). 
Debevec, P., 2005: Making "The Parthenon". 6th International 
Symposium on Virtual Reality, Archaeology, and Cultural 
Heritage, VAST 2005, Pisa, Italy. 
Dietrich, A., Gobbetti, E. and Yoon, S.-E., 2007: Massive- 
model rendering techniques: a tutorial. IEEE Computer 
Graphics and Applications, 27(6), pp. 20-34. 
El-Hakim, S.F., 2006: A sequential approach to capture fine 
geometric details from images. International Archives of 
Photogrammetry, Remote Sensing and Spatial Information 
Sciences, Vol. 36, Part5, pp. 97-102.