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1 October 2006
3D rock carvings recorded with simple equipment

A method of imaging rock carvings in 3D using everyday electronic equipment could help document decaying carvings before they disappear forever, researchers say. Archaeologists are struggling to document many rock carvings before they are eroded by pollution or weather. Bulky laser scanners can capture detail in 3D down to 0.2 millimetres. However, such instruments are too costly and cumbersome for general use.
     A system being trialled by archaeologist Kalle Sognnes and colleagues at the Norwegian University of Science and Technology and The Foundation for Scientific and Industrial Research (SINTEF) in Trondheim provides a much simpler and cheaper solution. It consists of an ordinary office projector, a digital camera and a laptop running specially developed software. "We are trying to find something cheaper because laser scanners are so large and expensive," Sognnes said. "In some places we are coming to the end of these rock carvings, and we hope to document them before they are gone."
     Sognnes has been testing the simple scanning set-up on carvings held at the Museum of Natural History and Archaeology in Trondheim, Norway. The carvings date from the Scandinavian Bronze Age (900 BCE to 800 BCE). The equipment will also be tested this week at a site north of Trondheim, which features carvings of boats, elks, and whales, dating from 6000 BCE to 200 BCE. To scan a carving, the projector is used to illuminate it with stripes of light and dark, and the digital camera records the resulting pattern for analysis on the laptop. The technique has been dubbed 'structured light'.
     Although not as accurate as a laser scanner, it is sufficient to reveal distinctive marks made by different types of tool. "Looking at the tools used can help age carvings," Skotheim said. "We can also use this technique to look for signs of how erosion is happening or to distinguish very weathered, hidden carvings from surrounding rock."
     There is an urgent need for cheaper scanning solutions, says Tertia Barnett, an archaeologist documenting rock carvings in Northumberland, UK. "Laser technology is changing but is still very bulky and expensive, and it takes a lot of time to get it into place for a scan," she says. Barnett has been testing another cheap solution that involves taking two normal digital photos from different positions and turning these into a 3D image on computer. This can reveal details of about 2 mm in size, but Barnett believes the structured light method could be even better: "A cheaper method with higher accuracy would be a great help."

Source: New Scientist (18 September 2006)

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