The “Victory Towers”The "Victory Towers" of Ghazni, Afghanistan are among the last vestiges of the great Silk Road empire of the Ghaznavids, who ruled an area from the Caspian Sea to the Ganges Delta from the tenth to the twelfth centuries A.D. Ghazni was renowned as a center of learning and the arts, as well as a seat of conquest.
In July of 2011, architects from the U.S. National Park Service's Historic American Building Survey (HABS) embarked on a ground-breaking project to fully document the towers. Using high definition surveying, also known as laser scanning, Dana Lockett and Paul Davidson captured the elaborate terracotta details of each façade as well as the brickwork of their exposed foundations to a level of accuracy never previously achieved. Their work, sponsored by the U.S. Department of State's Cultural Heritage Center, is an effort to help cultural heritage professionals in Afghanistan preserve the towers by providing baseline documentation that will underpin future conservation and preservation activities.
In the FieldSurveying was accomplished using Leica's C10 terrestrial laser scanner and selectively placed targets used for free station registrations. In order to fully circumscribe the structures, each tower was scanned from six separate positions (or stations). Acquiring the same targets from each station allows the software to register individual stations to one another for a complete 3D point cloud. Capturing every single brick and surface proved difficult. Gaps in the data were unavoidable due to changes in topography as well as the inability to reach roof lines and openings. Security and safety concerns meant the survey had to be completed in two days allowing only enough time to scan the towers at medium resolution. The entire process was captured by Agnieszka Dolatowska, an archeologist and member of the Polish military, who joined Dana and Paul at the site and photo-documented the towers as well as the scanning process at the request of the U.S. Department of State.
The fieldwork and subsequent data analysis and processing that comprised the core of the Ghazni towers documentation are essential components of the HABS recording methodology. Unlike many laser scanning fieldwork exercises, the scanning of the Ghazni towers was not a "scan and can" operation, but involved substantial post-data-capture processing and analysis to ensure data integrity and to utilize it in the production of two-dimensional architectural drawings usable in preservation efforts at Ghazni. Reluctantly, the team accepted the reality that so gaps in the data exist, although every attempt was made to minimize and work around them.
|Left-Photo: Detail of the intricate brickwork on the Mas'ud III tower. Photo credit, HABS. Right-Photo: Flattened image of the brickwork overlaid by "point cloud" data from the laser scanner. Photo credit, HABS.|
Creating the Drawingshigh dynamic range panoramic photography. This created the existing condition drawings of each panel comprised of the towers' elevations. While several architects worked to complete the documentation, special efforts were made to bring two Afghan architects into the DC office through a partnership with the U.S. National Committee of the International Council on Monuments and Sites (US/ICOMOS) and its International Exchange Program. The two historic architecture specialists trained in the operation of the laser scanner and post-processing software to familiarize them with the collected data. They helped process the scan data into standard architectural line drawings, lending their knowledge of the designs and inscriptions adorning the structures.
In traditional HABS fieldwork methodology, laser scanning is always supplemented by hand measuring and other field techniques because the scanner captures only what it can 'see', and scans are affected by lighting, color, and other structure qualities. But the conditions under which Dana and Paul worked in Ghazni permitted only enough time for the scanning of the towers and did not allow for supplementary data acquisition methods. Nonetheless, many hours were spent smoothing and flattening the data to ensure as accurate representation of the towers as possible, meeting the highest HABS standards.