At the Nelson-Atkins Museum of Art in Kansas City, Missouri, the highlight of its Egyptian galleries is an elaborate and complete funerary assemblage from the tomb of a 2,300-year-old noblewoman named Meret-it-es. The initial room layout of the Egyptian galleries revealed the space would be optimized if the coffin was displayed in an upright position, as opposed to a horizontal position. The 2,300-year-old coffin is made out of wood and has several layers of paint on its surface. The wood shrinks and expands as it ages, and is also affected by its environment. Experts wondered whether the artifact would be adversely affected if it had a vertical posture.
Kathleen Garland, senior conservator at the museum, turned to Ryan Woodward and Epic Scan, a Portland, Oregon, company specializing in spatial measurement, advanced 3-D laser scanning, and mapping. First, the scanning process would reveal any movements in the coffins’ various components. And second, the museum wanted to record the entire surface of the coffin to serve as a baseline archive of its condition in case of damage in the future. As the coffin would settle into place during the coming years, a second scan could be performed, analyzed, and compared with the original coordinate data for structural variations.
The inner coffin is made from wood, pigment, gesso, and gilding, all of which cannot be touched.After assessing the scope of the project along with size and accuracy requirements, Woodward contacted Hexagon Metrology Services to employ the use of a high-precision Leica laser tracker and a noncontact Leica T-Scan hand scanner. The workable area around the coffin was roughly 20 ft wide × 20 ft long × 10 ft high. The Leica T-Scan’s measurement envelope was a 30-ft radius from the laser tracker. Epic Scan also used its Leica HDS 6000 system as a supplemental measuring tool to the hand scanner, which allows them to compare data and also document the 100-ft room where the coffin was housed.
“The technology we use for many jobs scans in a very small window—4 ft by 4 ft or smaller,” says Woodward, the director of business development at Epic Scan. “Because the size of the coffin was outside this window, you would have to stitch together multiple scans with the possibility of introducing error by always trying to do a ‘fit.’ We wanted very dense data spread out over a fairly large envelope. With the Leica T-Scan, you leverage its large measurement volume and the accuracy of a laser tracker. Instead of a single point sensor, the hand scanner shoots out a fan of laser beams that gives it full return over the object.”
Rina Molari, an application engineer from the Hexagon Metrology Services division and an expert-level user of Leica portable coordinate measuring machine (CMM) technologies, joined Epic Scan to scan the coffin. “The face of the coffin was very intricate with many colors and shiny areas painted with gold leaf,” says Molari. “The eyebrow area was defined in a flat black matte paint. This was a stark contrast. For many scanners, surface qualities such as shiny, matte, changing colors can be a challenge and often require different settings to accommodate these variables. With one pass of the Leica T-Scan hand scanner, the surface data were acquired and recorded perfectly.”
Rina Molari, an application engineer from the Hexagon Metrology Services division, scans the coffin of Meret-it-es using a Leica T-scan portable coordinate measuring machine (CMM).
The entire project covered a period of three days, with the first day used to set up the equipment, and size up the coffin and its environment. Woodward collected the 50+ million cloud points and headed back to his office in Portland. Post-processing the data can often be the most time-consuming process of the entire operation. However, in this case, the post-processing was significantly reduced due to the measuring envelope of the Leica T-Scan, as the data were collected in one unit in the same coordinate system.
“We compared the two coffin surfaces prone and upright positions,” says Woodward. “We created mesh data to generate an error map that is color-coded showing different gaps. The analysis showed that the main body of the coffin was very stable, and there was no movement in the body. In the upright position, we saw a shift in the foot. This particular piece is a removable component, so it was not a huge surprise. For archiving purposes, the museum has a viable base model now: a snapshot in time. From the dense and precise data set gathered with the hand scanner, we can produce anything the museum could want.”
Belinda Jones is the founder and owner of HiTech Marketing LLC located in Westbrook, Connecticut. For more than a decade, Jones has written articles and commentaries about manufacturing, engineering, quality assurance, CAD/CAM/CAE applications, and other high-tech topics. She has extensive experience in marketing communications, technical sales, and applications engineering. Before joining the computer industry, she was a broadcast copywriter for four years. Jones holds degrees in fine arts and mechanical engineering, and studied cultural arts in Europe.
