Laser Scanning for Cultural Heritage Applications

by John Ristevski
March 1, 2006
Cultural Heritage can be defined as monuments, buildings, or landscapes of "outstanding universal value from the point of view of history, art or science." These sites are often under threat from environmental conditions, structural instability, increased tourism and development, and they are most likely under-funded, and hence, inadequately documented and maintained. Laser scanning, in combination with other digital documentation techniques and traditional survey, provides an extremely useful way to document the spatial characteristics of these sites. This spatial information forms not only an accurate record of these rapidly deteriorating sites, which can be saved for posterity, but also provides a comprehensive base dataset by which site managers, archaeologists, and conservators can monitor sites and perform necessary restoration work to ensure their physical integrity. A digital record of these sites also facilitates their accessibility to a broader audience via the Internet. CyArk, a non-profit located in the San Francisco Bay Area, is constructing an archive and associated Web portal which will allow this data to be accessed by site managers, researchers, students, and the general public.

Cultural Heritage Documentation Projects
These two case studies show the potential for the use of digital documentation tools in the cultural heritage field for activities including general site management, conservation, restoration, and archaeological analysis. The digital datasets for these sites are both available through the CyArk portal (www.cyark.org).

Chavin de Huantar, Peru
Chavin de Huantar is located in the north-central Peruvian highlands at an elevation of 3,150 meters. It is a pre-Hispanic structure developed progressively from 1200 BC to 200 BC. The site consists of a number of "buildings," large platform mounds housing a complex underground gallery network which surround a number of sunken plazas. The site is one of the most significant early Andean civilizations and has been given UNESCO World Heritage status. It is under threat from both urban encroachment and from the general instability of the surrounding mountainsides, which has led to a number of landslides.

The documentation project was conducted by the University of California at Berkeley in conjunction with the Stanford University archaeological project and supported by the Kacyra Family Foundation. Two field seasons have resulted in a comprehensive documentation of the site using both long and close range laser scanning techniques. A Leica HDS 2500 scanner was used to document all exterior surfaces of the complex and a number of underground gallery segments. A comprehensive control network was placed throughout the site and extended into the gallery network. This facilitated the registration of above ground and below ground scans to produce an accurate model of the site.

This dataset was used to calculate the depth of parts of the gallery network to assess the overburden as part of an ongoing analysis of the structural stability of the galleries. In the Rocas Gallery, parts of which have suffered collapse, scan data was used to predict the location of new perforations, which were being dug by the archaeologists to help clear the collapsed section of the galleries. Scans were also taken of the excavated

Circular Plaza Atrium, an excavation which revealed pre-Chavin structures where the intention was to expose and record and then re-cover the structures. Extensive close range scan data was also collected. The Minolta Vivid 910 was used to scan the Lanzon, a 4.5 meter high, elaborately carved stone monolith in addition to a large number of elaborately carved plaques. This dataset will be the basis for producing the spatial products needed to perform an initial condition assessment, an important part of developing an overall conservation plan for the site. In addition the data will also be used for ongoing monitoring of the site.

Mesa Verde, United States
Mesa Verde National Park is located in southwestern Colorado and contains some of the most impressive standing architecture in North America. It is best known for its unique cliff dwellings, adobe buildings constructed within recessed cliff alcoves. Spruce Tree House was the focus of a pilot digital documentation project to test the applicability of digital documentation techniques to replicate the traditional mapping and survey methods used by the National Park Service. Spruce Tree House is a large complex containing about 130 rooms and 8 kivas (circular ceremonial chambers) and is built into a recess 66 meters wide and 27 meters deep. The project was a collaborative effort between the University of California at Berkeley, Texas Tech University, the National Park Service, Insight Digital, and CyArk.

The project utilized three scanners, two long-range scanning systems, the Leica HDS 3000 and 2500, and a close-range scanning system, the Minolta Vivid 910. The long-range scanners were used to document the standing architecture and surroundings while the close-range scanning system was used for the documentation of wall details and artifacts. A Leica total station and Trimble differential GPS unit were used to geo-reference the point-clouds and provide additional survey control. In conjunction with the scanning, high resolution panoramic imagery was collected using a Nikon D70 camera and a custom-built panoramic photography rig.

The data was used to construct a high resolution photo-textured model. From this model, plans, sections, and detailed elevation drawings were produced to support the condition assessment activities of the Park Service. The existing process includes very detailed wall elevations which show features down to a centimeter in size. These features are often embedded within the mud-brick walls and exhibit very little relief in comparison to the wall. To facilitate the recording of these features the high resolution panoramic images were registered to the point cloud or mesh and ortho-rectified images of wall segments were produced to enable the mapping of these features. Based on this pilot project, time savings using these new techniques are estimated at around 80 percent.
Archiving and Dissemination

CyArk is dedicated to the preservation of World Heritage Sites through the CyArk 3D Heritage Archive, www.cyark.org, an internet archive which is a repository for heritage site data, obtained through laser scanning, digital modeling, and other state-of-the-art spatial technologies. This archive serves both education and historic preservation, and exists now in a prototype stage. In its fully developed state, the 3D heritage archive website will be an accessible, global collaborative network of servers working off a common database architecture and storing dimensionally precise and visually rich 3D point cloud data wrapped with high definition, high dynamic range photography, representing heritage sites from around the world. The CyArk portal provides a Web interface that will enable users to search the archive spatially, locating media (including photography, scan data, text, CAD drawings, 3D models, and animations) that relate to specific parts of a site. Users can view this data dynamically and download high resolution versions of these data products. Most importantly, each media item is attached with essential metadata that will facilitate the reuse of this information. This metadata includes the "who, what, where, when, and why" information that users require to be able to understand, interpret, and make use of the data. The archive will also ensure, through a migration program, that these datasets are accessible into the future.

Summary
An integrated method that utilizes a range of tools from laser scanning to traditional survey and high-resolution digital photography are highly valuable in the field of cultural heritage where high accuracy and comprehensive documentation of sites are needed on a regular basis. These techniques can often result in significant time and cost savings compared to traditional survey methods, and provide a much more accurate and more detailed record of the site. Through organizations such as CyArk, this data can be made accessible to a much wider audience, enabling not only site managers and archaeologists access, but also facilitating educational use of this data and opening up these sites to the general public through virtual tourism.

About the Author
John Ristevski directs the research and development activities of CyArk, a project of the Kacyra Family Foundation dedicated to the preservation of cultural heritage through high definition documentation. He is also a lecturer at Stanford University in the Civil and Environmental Engineering Department where he teaches surveying and geomatics.
Related Projects:
Chavín de Huántar
Mesa Verde