Mapping Djoser's Step Pyramid
A laser scanning survey is the latest technology used to record the recent state of Egypt's oldest royal stone complex, Nevine El-Aref
Sunrise at Saqqara, and all is well on the necropolis. It is, as usual, silent, peaceful and still out here in the desert. Last Tuesday, however, the serenity and divinity were broken by the arrival of an American-Japanese scientific mission to carry out a laser scanning survey of Djoser's Step Pyramid. At the footsteps of the pyramid were gathered dozens of people, from scientists to technicians, archaeologists and restorers to workmen, all there to witness the first ever endeavour to document, in detail, the present condition of the great and distinctive monument using a high-tech laser device in an attempt to create a virtual three-dimensional model of Egypt's oldest pyramid complex.
Carried on the backs of three professional climbers as they grappled to descend all four faces of the pyramid's six gigantic steps, the Zoser Scanner, a device created specially for the purpose, records data at the exceedingly fast rate of 40,000 points per second using infrared signals to gather coordinates and elevations of thousands of points on the monument.
"It is an archaeological salvage project," Culture Minister Farouk Hosni told Al-Ahram Weekly. He explained that such a project would not only provide a detailed map of the Step Pyramid but would also create a virtual three-dimensional model of it, which in its turn will be a valuable reference for architects, restorers and archaeologists involved in the restoration of the pyramid and for the continual monitoring of its condition.
Zahi Hawass, secretary-general of the Supreme Council of Antiquities (SCA), says the project falls within the framework of the commitment made by the Ministry of Culture and the SCA to protect and preserve Egypt's cultural and archaeological heritage. He points out that the survey is being conducted in collaboration with a Japanese mission headed by Kosuke Sato of Osaka University and an American mission led by Mark Lehner, director of Ancient Egypt Research Associates (AERA). This project intends on completing the archaeological documentation of the Step Pyramid in order to better understand its various stages of construction. A variety of laser scanners will be used, including the Zoser Scanner, which was custom designed to scan the pyramid by Develo Solutions of Osaka, Japan.
Sato pointed out that for more than 70 years French architect Jean-Philippe Lauer had comprehensively studied and restored the Step Pyramid complex. Although his seminal work was indisputably considered the foundational study on pyramids, his theories were based on his schematic plans and sections, which are not facsimiles of the actual state of the monument. In contrast to the scanned images produced by the ground fixed laser scanner in the previous season, Sato continued, the Japanese mission improved several aspects for laser scanning the Step Pyramid in order more evenly to dense point cold data, eliminating shadows created by obstacles between the laser scanner and the target as much as possible and providing a density of point clouds finer than 5mm mesh.
Sato said that he did not arrive haphazardly at the invention of a special device, but that it was an urge because the normal fixed laser scanner produced uneven point cloud data which were needlessly very dense at closer ranges, while less dense at a distance. "The developed scanner maintains a constant distance between the scanner and the pyramid," he said.
To avoid having an unscanned area, Yukinori Kawae from the AERA explained, the mission applied a multiple scanner system that simultaneously produced laser beams, even behind small protuberances. With this method, while surveyors scan and move at a constant speed, accurate information for the position and the attitude of the scanners can be gained.
The laser scanning survey of the Step Pyramid will take four weeks to complete, and next year the second phase for the pyramid's internal structure will start.
The Step Pyramid was built during the reign of King Djoser of the Third Dynasty (2687-2668 BC). It is the first pyramid in Egyptian history, and the earliest stone structure of its size. Over the years, the six steps of the pyramid have been exposed to natural erosion leading to their deterioration, and now a comprehensive restoration project is taking place in an attempt to save this great pyramid.