Mapping the well, digitally

Print edition : December 26, 2014

A member of Scottish Ten taking pictures for the three-dimensional digital scanning of Rani ki Vav stepwell, in October 2011. Photo: Sam Panthaky/AFP

AS part of its conservation effort in 2011, the Archaeological Survey of India (ASI) teamed up with the Scottish Ten team and CyArk to digitally scan Rani ki Vav. The Scottish Ten is a joint project of Historic Scotland, the national heritage agency; The Glasgow School of Art’s Digital Design Studio; and the non-profit organisation CyArk. Their aim was to “digitally document Scotland’s five UNESCO-inscribed World Heritage Sites and five international heritage sites using cutting-edge laser survey technology…. The project marries advanced scientific technologies with heritage conservation.”

In the case of Rani ki Vav, the purpose of scanning the vav was to bring the site to a much wider audience (see weblink at the end of the story) and raise its national and international profile. The scan will also serve to digitally conserve the site. The ASI will be able to use the accurate, high-resolution 3D survey for heritage management purposes.

The well was scanned over a two-week period in 2011. The greatest challenge was the sheer number of carvings and their details. The Scottish Ten site says: “We used a number of new and adapted 3D scanning technologies to deal with this and also incorporated digital photogrammetry into our fieldwork programme. Scanning the interior walls of the well itself was a significant technological challenge. Access is difficult and ensuring we could scan all aspects of the surface was challenging. We developed and built a special rig which we used to suspend the scanner over the edge of the well. This rig could be lowered down the well to capture the carvings on its walls in 3D. The temperature was between 38 and 40°C, which was not only a challenge for the team, but for our equipment as well which we had to keep as cool as possible.”

The website describes the technical process: “3D laser scanning is a rapid, non-contact, accurate and objective method for digital documentation of the built environment. Laser scanning allows for the accurate recording of 3D surface geometry of objects in a digital form. A large amount of 3D data can be collected within a short period of time. The laser beam scans the object surface up to 1 million times every second. The returning reflected laser light is used to compute the distance to the surface. This means up to 1 million spatially accurate coordinates (or points) are collected every second. The millions of points computed are used to produce a ‘point cloud’ which defines the surface geometry of the building or monument of interest…. The data generated by the laser scanner is a ‘point cloud’: a collection of xyz coordinates…. Point clouds are acquired from several points of view and joined together to produce a 3D image with accurate dimensions…. 3D objects need to be scanned from several angles to obtain the optimum amount of data. The number of scans required at each site depends on the intricacy of the object; complex objects require more angles of view to ensure that important detail is not missed. There needs to be sufficient overlap between scans to enable them to be joined together into the 3D model. In most cases surveying targets are used to join individual scans. Ideally, at least four should be visible from each scan position to enable the scans to be ‘registered’ together with a good degree of accuracy.”

The number and the intricacy of the carvings, coupled with the complexity of the process led David Mitchell, Director of Historic Scotland Conservation Group who led the Scottish Ten team, to write in his India trip journal which is available online: “The stone carving is endless and exquisite. The sharpness of detail is remarkable…. The scale of the carving had us in awe… we looked at each other, incredulous, but determined that we could do this. The logistics are challenging, you could spend years here with a hand scanner and would also need to develop some new techniques.”

For a 3D tour of the stepwell, see: https://www.youtube.com/watch?v=2IsUXQ8xdGA

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