This site chronicles a photogrammetric study of the Great Temple in Petra, Jordan. The photography for the study was completed during the 1998 summer dig season. During the fall,1998 and spring, 1999, photographs were scanned and used to build a 3D model of portions of the temple proper (see temple plan) using PhotoModeler Pro software to process the photos. The project was completed by Eileen Vote with cooperation from Martha Sharp Joukowsky, the head archaeologist in charge of excavations at the Great Temple Site in Petra, Jordan and with help from LEMS - Laboratory for Engineering Man - Machine Systems, a vision studies group at Brown University. We plan on extending our collaboration to form the Digital Archaeology Group.

 

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Standard Survey Method in Archaeology

From the Five Year Report:

Our general approach to survey (and its primary objectives) is to automate and integrate the collection of field data. We used a series of programs to chart and document the site, and the systems we deploy have proven so successful that they have been used as the model for other archaeological field operations. We utilize software packages that include CADD program (MiniCad 6) and the COMPASS/Foresight program, a survey data acquisition and plotting package developed at the University of Pennsylvania Museum. These software packages combined with our use of a Topcon laser transit, ensure the continuity of all our data files. Our system, therefore, is a combination of computer hardware (Macintosh laptop computers) and software that allows input, editing, storage, retrieval and display of spatially referenced data.source 1

Standard archaeological survey procedures currently are comprised of EDM Surveying on-site performed with a computer controlled theodolite which registers elevation points and top plan features of the Great Temple and its surrounding areas (lower temenos, exedri, adjoing site features). Unfortunately, it's too costly to record elevations or characteristics of the z dimension. Archaeologists are interested in finding an affordable way to record 3D characteristics of architectural features so that a complete record of the disturbed site can be kept and also for advanced spatial analysis.

 

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Photogrammetric Process

Example of Configuration of Images Taken of Anta-Particia in the Temple. The standard is to photograph in a ring around the subject.

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Steps for Producing a Model

 

Photograph the Project and Camera Calibration

Photographs of the entire project must be taken with the knowledge that, for processing accuracy, one will need three images of each element with a good degree of angular separation between each image. The shots above illustrate that fact. Each photo is taken at a different position but there is enough overlap to reference features in at least two of the images. For a facade survey it is best to have a minimum of three overlapping images. However, in some cases, it is very difficult to get a clear shot of a feature from multiple angles. This problem occured in the western aisle of the temple. It was not possible to get a clear image of the whole elevation so it was neccessary to take incremental shots at 3 foot intervals, a time consuming endevour.

To ensure a high level of accuracy the camera/lens setup was calibrated using a program supplied by PhotoModeler. This process determines the degree and extent of error present in the lens so that each image produced by it can be corrected in the PhotoModeler program.

Import Photos

The photographic slides were scanned at a 1200 dpi, formatted as jpeg files and imported into the PhotoModeler Pro program for marking, referencing and processing. This process was time consuming and proved that it would have been easier to use a digital camera for image acquisition.

Marking and Referencing Photos

Using a series of photos of an area of the temple, object points are marked on each photo, then referenced between photos.


Scaling the Model

This is done by telling the program the real distance between set points measured during the recording procedure. I used control points surveyed by the team surveyor. He was able to take several points on each elevational face which were marked with black tape. After marking those control points on related photos exact dimensions in global position were added to the resulting model.

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Models Generated

Patricia-Anta and Paul Engaged-Column  (click image to enlarge and notes)

Anta, Engaged-Column and Western Corridor (click image to enlarge and notes)

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Accuracy Rates and Results

Accuracy rates varied from a near +/-2 centimeter accuracy where clear shots of the elevations could be taken with a variance in camera angle from three points of view. Accuracy was much lower +/-10 centimeters in the areas where it was more difficult to get a clear view of the elevation, particularly in the western corridor.

With a digital system of data acquisition, marking, referencing and processing images would be much faster and ensure fewer mistakes. If the system were simplified it would be an excellent alternative to 3D laser transit stations currently being used by archaeologists. A process of photogrammetric survey would be a cheap, efficient way for archaeologists to gain 3D information about their sites.

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References

Introduction to Photogrammetry
Advanced Photogrammetry - Atkinson's Theory of Close Range Photogrammetry
Photogrammetry and Imaging Archaeology
Bibliography of Sources on Photogrammetry in Archaeology 
Technology Used in the Excavations at Petra
3D Modeling Links - Where is 3D Modeling Headed?
Archaeologists and Researchers Using Photogrammetry and Advanced Survey in Archaeology

British Computer Applications in Archaeology:
Computer Applications in Archaeology
Surveying, Mapping and Photogrammetry Presentations 1999 Dublin Conference Proceedings

 

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Sources:

1 Joukowsky, Martha Sharp. 1998. Petra Great Temple, Volume I, Brown University Excavations, 1993-1997. pp.51-52. Providence, Rhode Island: Martha Sharp Joukowsky.

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Brown University
Department of Architectural History and The Center for Old World Art and Archaeology
page developed by Eileen Vote. Eileen_Vote@brown.edu