|Technology and the Excavations of the Temple|
For ten years, under the auspices of the Jordanian Department of Antiquites, Brown University has been excavating in Jordan at the Petra Great Temple. Our research, beyond excavation, is the purpose of this article for a better understanding of the elusive Nabataeans who constructed the Petra Great Temple. Scientific applications we have used include: surveying with Geographic Information Systems (GIS) and Global Positioning Systems (GPS), Ground Penetrating Radar (GPR), artifact studies and databases, and analyses including Instrumental Neutron Activation (INAA), fresco pigments, palynology, marble isotopes, stone weathering, and dendrochronology. It should come as no surprise that all of these are techniques that are dependent upon the expertise of our team members. This submission, however, will focus on a discussion of our digital archaeology project and the 3D Free-Form Models for Geometric Recovery and Applications to Archaeology. A chart showing various areas of scientific methods is shown in Figure 1.
The Great Temple
Let us picture a Nabataean king exploring the heart of central Petra seeking the location for a monumental building. Perhaps he walked along the Wadi Musa, rounded the point near the Nymphaeum and reached the area where looking up the imposing hillside to the south, he was greeted by the view of a rocky escarpment. Favorably impressed by the impressive hillside, it was here he decided to build the most important precinct of the city. That the monumental Great Temple was constructed on this rise is not difficult to understand. Its location was far enough from the entrance to the city for protection, yet close enough to the other freestanding structures—the Qasr al-Bint and the Temple of the Winged Lions to serve as the nexus for Nabataean religious life and administration. With thousands of chisels, the Nabataeans sculpted the bedrock and created artificial terraces where bedrock was absent to create a tri-tiered design for the precinct. This was to be a showplace to stand in a prominent position, high above the neighboring buildings. Figure 2 is a digitized plan of the precinct and Figure 3 shows an aerial photograph of the site after the 2001 excavations. The Great Temple Web Site is located at http://www.brown.edu/Departments/Joukowsky_Institute/Petra
Brown University researchers in Engineering, Computer Science, Applied Mathematics and the Center for Old World Archaeology and Art and Department of Anthropology have designed software that allows archaeologists to model and reconstruct columns, buildings, statues, and other complex shapes from photos and video. The multi-disciplinary research effort has been funded by a three-year 1.2 million-dollar Knowledge and Distributed Intelligence Initiative (KDI) Grant from the United States Government's National Science Foundation (NSF). The grant was part of a NSF initiative in information technology, with awards directed at difficult computational problems requiring multidisciplinary approaches. Besides the author the other principal Brown University investigators in this digital multidisciplinary effort included David Cooper, and Benjamin Kimia, engineering, David Laidlaw, computer science, David Mumford, applied mathematics, and post-doctoral student Eileen Vote and doctoral candidate Frederic Leymarie. Researchers Talal S. Akasheh and his team at the Hashemite University, Jordan, including Fawwaz Ishakat have been instrumental to our success. The first purpose of this project is to create a three dimensional understanding of the Great Temple site.
The Brown University SHAPE Lab is a 900 square foot facility that houses 11 work stations (SGI's and PC's), a laser scanner, and a fish tank with a Virtual Reality (VR )set-up. There are three post-doctoral researchers, nine graduate students, and seven undergraduate students, who spend most of their time working in the lab. Collaborators from Leed's University and Paris, each spend roughly a month a year, drawing heavily on our facilities. Additionally, two graduate students from Universitat Autonoma de Barcelona, Spain and a professor from Sabanca University, Istanbul, have been visiting for a few weeks each summer and they use the lab heavily. The SHAPE Laboratory has been building archaeology and 3D shape databases and software. Some of these databases are commercially available while others have been developed within the lab.
Scientists at Brown University in the Shape, Archaeology, Photogrammetry, Entropy (SHAPE) Lab have realized ARCHaeology in Virtual Environments known as the ARCHAVE system which allows archaeologists to explore the reconstruction of the Petra Great Temple site in a Computer Augmented Virtual Environment (CAVE). Team archaeologists have built a three-dimensional model of the Great Temple precinct. They then implemented the interface to investigate the building in three-dimensions at a life-size scale in the CAVE which is an eight-foot-by-eight-foot square room with large video screens. When the archaeologist researcher enters the CAVE, they put on a pair of glasses that allow a computer to record their movements and help them explore the reconstruction of the Great Temple. (We use a hand-held mouse to move around the three-dimensional model and look at different architectural details.) This system even allows us to take a virtual flight over the temple precinct. We have enjoyed enormous recognition with this project. In the references is the paper that won the "best case study award" at this year's IEEE Scientific Visualization conference and our researchers have contributed to video segments on the National Broadcasting Company "High Tech Archaeology" and a Public Broadcasting Station Documentary, "2002:A Space Odyssey—30 Years Later." The SHAPE Web site can be accessed at http://www.lems.brown.edu/vision/extra/SHAPE/
Petra Great Temple artifacts range from pottery fragments to ornate capitals. To further develop the ARCAVE system, our researchers are using images of objects and the databases obtained from the Petra Great Temple 10 years of excavations. At best reassembling archaeological artifacts by hand or through the use of images is laborious and time intensive, and often impossible because pieces or features are missing. Current computer algorithms can only recreate simple structures such as spheres, straight lines or cylinders automatically or with little human intervention. Reconstructing complex shapes usually requires considerable human intervention using the computer. Progress has been made on a number of topics including: medial axis, generalized cylinder, ridge and high curvature-point, representation and estimation for curves and surfaces; automatic estimation of mathematical models for ceramic pots and inscribed marble fragments. These reconstructions have been made from 3D dense laser scans and images of small fragments found at the Petra Great Temple. So not only have we created the virtual reconstruction of the Great Temple but also we have created a 3D immersible visualization in the CAVE with its associated trench finds.
The laser scanner in our SHAPE Laboratory has a depth of field from a few inches to a few feet, collects 150,000 x, y, z, points per second, and has a resolution of roughly 0.25 mm. It, and its associated geometric modeler software, is used in our Shape Stitching via Interactive Transactions between Computers and Humans (the STITCH project). It considers the complex problem of the re-assembly of fragments into complete objects from 3D measurements e.g., for pottery sculpture, frescoed murals, column capitals, bones, portions of buildings, and other architectural structures. STITCH also is starting to be used in pattern recognition computer vision courses, and also is being used in digital, virtual and real sculpting research, in a joint project between the art department and engineering. A fish tank immersible VR environment now is being assembled and will be available for immersible viewing and interacting with 3D surfaces and objects. This will aid 3D shape analysis, manipulation, and inference from data, and will aid in semiautomatic object (i.e., sculpture, column capitals, large structure) and archaeological site reconstruction. The software, both commercial and algorithms developed under the KDI project has been and is continually being organized for general use within the lab. This includes 2D and 3D-shape representation, estimation from data and matching, and general 3D-shape and data manipulation and visualization.
A second purpose of the digital SHAPE project is to construct as complete a record as possible of the nine years of excavations in a way that is fast working and easy for people to access. Constructing three-dimensional models to make precise geometric measurements for small artifacts and large structures at a site may allow us to reassemble it. We also have developed a VR system to recreate 3-D scenes of the Great Temple. Figure 4 shows a VR reconstruction of the Great Temple.
The project is designed to develop more descriptive and effective ways of using computers to model and make inferences about three-dimensional shapes and surfaces. The project's other major goals are to:
It is hoped that we will be able to have an archaeologist use VR to look at an area under excavation as if that person was actually there and to make precise geometric measurements of small artifacts and large structures. As we said above, the project is designed to develop more descriptive and effective ways of using computers to model and make inferences about three-dimensional shapes and surfaces. Other major applications of the work are to use computers to reconstruct models and images of objects in their original conditions from images of found artifacts, categorize reconstructed objects into like groups, relate them stylistically, and compare them to similar objects found at other sites. This technology could also help archaeologists determine where objects originated, and trace both ancient trade routes and the stylistic influences between sites. The researchers expect the software systems prototyped will also boost computer modeling capabilities in other fields, including manufacturing, architecture, historical research, video conferencing, and searching image and three-dimensional databases over the Internet.
In essence, the project is looking at new approaches for handling huge amounts of complex image data from single images or from video of complex freeform shapes in order to build three-dimensional models. We are now approaching the site as we would an open-air exhibition and have done what we could to enhance its setting both in the field and in the laboratories at Brown University. In the publication of the Great Temple Excavations, Volume I, with its accompanying CD-ROM, the account of our first five years of excavation, 1993-1997, we have sought the presentation of information in a “permanent” manner, so that visitors either in Petra itself or in any other part of the world who have access to our data, have an increased awareness as to where they are as they tour the site—this is a primary objective of archaeology. It is not only the preservation of the Great Temple, but the site’s interpretation and a long-term dialogue about its remains that we are after. Even when we are not working in the field, we believe that we can make a contribution to the visitor who will learn by moving around and looking at various sectors of the precinct. The circulation pattern is important and will be especially adapted for the visitor to interpret the site, and thereby be informally educated about what they are experiencing. Either on site or in the CAVE, the visitor can study the site, and only the site itself brings substance to the architecture. As the site is the primary tangible evidence of the excavation, it communicates itself directly to the visitor. It is unique, as is its setting and its architecture.
3D Free-Form Models for Geometric Recovery and Applications to Archaeology
An additional project we will be undertaking during the 2002 field campaign is 3D scanning and imaging with both still and video cameras. A record will be made with video coverage of the trenches, 3D scanning of pottery, elephant headed capitals and other artifacts. This will further our virtual reconstruction of the site.
With NSF support, we are beginning to develop a technology for the recovery of 3D free-form object and selected scene structure from one or more images and video. The technique is based on the development of 3D-shape representation and a semi-interactive mixed-initiative system along with machine decision-directed Bayesian surface-estimation. The main focus of the effort is the development of useful tools for archaeological site and artifact reconstruction and architecture. This will impact low level shape models and how they are assembled to form either more complex objects or complete ones. The latter condition often occurs at archaeological excavation sites where objects are found in pieces or have been damaged from destructive forces or erosion.
Despite recent substantial progress in automated scene recovery in computer vision the challenges presented by free-form shape extraction and assembly are still great. The researchers employed an interactive approach in which a user can guide the recovery process or can be available when requested for assistance by the machine in the complex task of assembling many fragments to re-create a large or complicated object. The intent is to develop the fundamentals of a user-controlled technology for the benefit of the naïve user. The ultimate goal is to enhance productivity in interacting with large amounts of complex visual data by modeling the underlying 3D structure. This project already has provided new practical tools. It will also provide an effective test bed for 3D shape reconstruction and recognition, more descriptive local and global models for working with 3D shapes, a better understanding of human/decision-making-machine interaction for free-form geometric modeling, and for extracting 3D geometry from one or more images and video and associated computational complexity issues.
As applied to the field of archaeology this technology will provide improved surveying methods with an advanced archaeological record and a means to conduct high-level analysis not heretofore available. It will further permit the transfer of reconstruction capabilities from the artist directly to the archaeologist. Since the problems resolved in the archaeological context are to a significant degree generic and thus transferable to the fields of medicine and industry. The potential impact is extremely broad. In the past six months, team members working on the ARCHAVE project integrated more Petra Great Temple site data and focused on designing and implementing new visualization methods to improve user performance with Immersive Virtual Reality (IVR) queries.
There have been two visiting graduate students helping reconstruct and model sections of the site that were previously inaccessible; i.e., the Petra Small Temple and the Cryptoporticus. In addition, several undergraduate students built trenches based on data from the team. These efforts give us a much larger representative sample of the site with which to integrate 3D finds and visualize new database information.
The team also has been working on new ways to visualize multivariate data at different scales in order to allow users to look at a much larger sample of the site data at once. This is being accomplished by developing graphic methods for dealing with the transition from small to large scale.
Brown University academic departments and strengths represented by the faculty and their inquiring students are using the SHAPE Lab to cover a broad spectrum of disciplines. The three post doctoral researchers represent applied mathematics, archaeology, and engineering, the graduate students represent archaeology, engineering, applied mathematics, computer science, and the undergraduates represent archaeology, computer science, engineering and art. Working together in the SHAPE Lab has resulted in research, technical growth, and educational broadening that could not have occurred otherwise. Great excitement and strength are brought to this project because of the broad range of interests and expertise of the participants.
Petra electronic databases have been constructed and are under continuing development, with highly sophisticated capability planned—the project does continue to be implemented, because we have just been informed of the receipt of an NSF 2 million-dollar follow up four year grant to continue this research. A team is going to Petra in 2002 to collect laser scan data, digital images, and video for use in research on object representation and object reconstruction from potsherds, artifacts, and large eroded structures based on one or more of the preceding data types. This will go into the available databases in support of research and prototypes for illustrating what can be done.
Our Petra Great Temple excavations have produced the primary material evidence for the architecture and artifacts concerned with our understanding of the Nabataeans and their environment. Our team is involved in the research of the site, which is directly related to its archaeological objectives. The archaeologist obviously has an important role in the research and the publication of the results. We have outlined the disparate techniques we have used, but we are asking many more questions about the Great Temple and the urban fabric of Petra as a whole. Two thousand years ago, 30,000 people lived in this leading city with plastered cisterns, piped in water, sophisticated houses, baths, some 800 frescoed tombs, a theater cut out of the living rock, frescoed temples—a population of merchants, but those also who cultivated fruits and vines. In using modern technology, we are even more appreciative of the Nabataean technologies, which allowed them to adapt the desert to their needs.
References for this submission can be found on the SHAPE Web Site.
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