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February 5, 2010 — Ottawa, Ontario
NRC scientists who measured the Mona Lisa's smile with laser precision recently gave similar scrutiny to an ancient temple on the Acropolis.
Specialists from the NRC Institute for Information Technology (NRC-IIT) scanned and photographed the Erechtheion temple, located near the larger Parthenon, then used software to assemble a highly accurate three-dimensional digital model for Greek cultural authorities.
Scanning took five tightly scripted days — and 10 full days beforehand just to plan every move.
"Everything was calculated to the minute — it's not as easy as a laboratory setup," says Jean-Angelo Beraldin of NRC-IIT. "In a typical one hour scanning session, you end up with a billion data points. If you spend five days, you can imagine the amount of data you generate."
The 20-by-10-metre (5-metre-high) temple's size was a challenge. To scan a top view, Beraldin's collaborators flew digital cameras over the site on a balloon. Team members wrangled laser scanners around the rocky Acropolis to ensure good sight lines on walls, all while fending off questions from curious tourists.
While Beraldin's team has scanned 3D images of smaller cultural items at hair-fine resolutions of 70 to 80 micrometres, they laser-scanned most of the Erechtheion at a less-demanding, but still detailed, one millimetre resolution. Even so, their laser scanner acquired 500 megabytes of data in every minute of operation over most of the five days.
The result, after processing with software developed at NRC (called Atelier3D.ca), is a 3D model that shows measurements and surfaces accurately as the temple stands. The team is still working on rendering the true colours of the original, says Beraldin, because viewers who see the virtual model need to feel as if they're looking at the real thing.
From the model, Greek cultural authorities can create "orthophotos" — detailed architectural drawings — of the Erechtheion's current state, giving an accurate real-life baseline from which to monitor surface and other changes.
"It's important to document monuments and artifacts the way they are at a particular time," says Beraldin. "If there's an earthquake, for example, cultural authorities will have the original locations of all of the different stones and marble pieces in the structure."
The virtual temple also gives curators a starting point from which they could rebuild a digital model of the original, or pre-test any repairs, without touching the real thing.
The Erechtheion, completed around 406 B.C., has been partly restored. The six female statues incorporated into the structure, known as "caryatids", are replicas cast from originals at the Acropolis Museum and the British Museum. They and other recent reconstruction efforts are made with newer materials that contrast in colour and texture with authentic sections. The roofless temple's incomplete walls carry graffiti, cuttings, and rifle and cannon damage from relatively modern wars. As artifacts of the classical temple's more recent history, these signs of reconstruction and damage were recorded accurately as part of the project.
Beraldin says cultural projects around the world have helped to shine the spotlight on NRC technology that his team is actually developing for industrial uses.
"The Erechtheion was a good test case, but we always make sure the technology can be used in other fields," he says.
Some 3D techniques developed at NRC are used in animation and gaming industries, as well as in other areas. "Optical non-contact measurement" uses devices such as laser scanners and photographs, and accompanying software programs, to monitor the state of buildings and infrastructure for maintenance and security purposes. The same kind of scanning technology allows large aerospace manufacturers to reliably reproduce and inspect complex 3D engine and body shapes, ensure that airframe pieces built in far-flung factories will assemble correctly, and rebuild engines to like-new tolerances.
In medicine, Canadian surgeons have recently begun testing digital 3D techniques developed at NRC to plan and practice tricky brain procedures before operating. They can test different approaches on virtual models of individual patients' brains, synthesized from huge amounts of data on standard computers.
"What we did in the cultural field is now being tested in the medical field," says Beraldin. "There are benefits for the cultural field, but also benefits for Canada. We make sure there's a good return on the investment."
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