Senin, 21 Juli 2008

Photogrammetry at the Acropolis

After a few weeks offline I'm now back and writing from Liege, Belgium. During my time off I had the opportunity to visit the Acropolis in Athens, Greece. While walking up to the Parthenon I noticed there was a terrestrial laser scanner set-up and operational - although unfortunately I didn't get any photos. But that was enough to get me wondering what the project was about. At the top of the Acropolis I found a sign with a short description of the project (photos below). Since it is difficult to read I have reproduced the text below:

DATA ACQUISITION FOR THE PHOTOGRAMMETRIC RECORDING OF THE ACROPOLIS

The Acropolis Restoration Service carries out the project of geometric documentation of the Acropolis hill, the circuit Wall and the Erechtheion, using photogrammetric methods together with 3-dimensional scanning.

All the information to emerge is to be entered in a Geographic Information System (G.I.S) that will be available through the Acropolis Restoration Service's web site (ysma.culture.gr).

Photogrammetry at the Acropolis was also a subject of discussion at the recent ISPRS Conference in Beijing. One of the technical sessions (TS-SS19) was "Recording and Documenting the Acropolis of Athens - From Classical Ancient Greece to Modern Olympics". While I wasn't at the conference, a colleague sent me the paper for "Recording, Modeling, Visualisation and GIS Applications Development for the Acropolis of Athens", by Tsingas et al. The paper discusses the various techniques employed by the project outlined above, which include geodetic field measurements, terrestrial scanning, and photogrammetric data capture and processing. Of the many data products to come out of the project, an interesting one is a top-view orthomosaic with a 10mm resolution. A 22MP camera was used on a balloon system, as motorized vehicles such as helicopters are not permitted to fly above the Acropolis. Also of interest (and news to me) is that Leica Geosystems is a partner in the project. One of the terrestrial scanners is a Leica HD3000, while ERDAS LPS is used for parts of the photogrammetric processing. This included camera calibration, bundle adjustment, and terrain processing.

The paper describes the methodology in detail, and I will see if it is available online anywhere - it provides an excellent discussion of various techniques used in concert to fully capture a highly detailed digital version of the monument. A few other good papers on photogrammetry/mapping at the Acropolis are here and here.
ARMU

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