same object. If those views don’t exist, the image remains flat. Also, quality, while improved with more cameras, tends to be uneven. And photo-based modeling is only effective in places that are accessible to a camera.

Laser scanning combined with photometry comprises a much more reliable solution for applications that require it. That’s the combination Katsushi Ikeuchi, a professor in the Institute of Industrial Science at the University of Tokyo, and colleagues used in capturing the Bayon temple, a complex of sacred structures in Angkor Thom, Cambodia that covers more than five acres. Ikeuchi’s team used laser-measurement devices mounted on scaffolding, ground-level tripods, and a cherry picker to determine surface depth in places where those conventional approaches could reach. To scan down narrow corridors it added ladder-mounted climbing scanners, and for points high on the 40-meter- tall temple it scanned from a tethered balloon, in both cases developing software to compensate for the scanners’ sometimes-unpredictable motion.

The Bayon Digital Archive Project gathered more than 10,000 range images totaling more than 250 gigabytes of data, measuring the entire site to a resolution of at least one centimeter. Because the data set was so big, several new algorithms were needed to match and align the points into a 3D mesh.

Instead of the “next-neighbor” alignment algorithm previously used, the Bayon temple team developed a two-step process that quickly identified matching pairs at the time of data capture, thereby converting the ultimate calculation from N2 to N complexity. Later, the points were aligned simultaneously on a parallel processor cluster in a week of processor time—a 14-fold improvement over what the team claims was needed under existing algorithms.

The final model was important in two regards. First, it captured details of the 800-year-old temple, which is in danger of collapse. Second, it made comprehensive computer-aided scrutiny of the site possible—a benefit that bore fruit when the team was able to definitively categorize the temple’s 173 carved stone faces in a new and significant way.

Similar results came from laser-scanned models at another histori-

cal site, the mausoleum of Henry VII, a 14th-century King of Germany. The monument comprises many parts that have been moved, lost, changed, and amended over the intervening 700 years, and the project’s goals were both reconstructive and educational. As Clara Baracchini, officer at Superintendency for Environmental, Architectural, Artistic, and Historical Heritage of the Provinces of Pisa, Livorno, Lucca, and Massa Carrara, and colleagues noted, the project could be used “to teach medieval sculpture to students and to let them try to reconstruct the original monument from the disassembled components.”

But while laser scanning can create models of unsurpassed detail, the main problem with it is that, as Georgia Tech Associate Professor Frank Dellaert put it, “You can’t do it in the past.” On the other hand, photo-based approaches lack some of laser scanning’s advantages. The two approaches differ greatly in approach, cost, and purpose, but both have already proven themselves invaluable for historians and researchers.

 

Further Reading

Xiao, J., Fang, T., Tan, P., Zhao, P., Ofek, E., Quan, L. Image-based façade modeling, ACM Transactions on Graphics 27, 5, December 2008.

Agarwal, S., Snavely, N., Simon, I., Seitz, S.M., Szeliski, R. Building Rome in a day. International Conference on Computer Vision, Kyoto, Japan, 2009.

Schindler, G., Dellaert, F., Kang, S.B. Inferring temporal order of images from 3D structure. International Conference on Computer Vision and Pattern Recognition, Minneapolis, MN, 2007.

Ikeuchi, K. and Miyazaki, D. Digitally Archiving Cultural Objects. Springer, New York, NY, 2008. Ikeuchi, K. UTokyo’s e-heritage Project: 3D Modeling of heritage Sites. http://www.youtube.com/ watch?v=DPiMJkZ0YKI. Baracchini, C., Brogi, A., Callieri, M., Capitani, L., Cignoni, P., Fasano, A., Montani, C., C. Nenci, C., Novello, R.P., Pingi, P., Ponchio, F., Scopigno, R. Digital reconstruction of the Arrigo VII funerary complex, VAST 2004.

Tom Geller is an oberlin, oH-based science, technology, and business writer.

© 2010 aCM 0001-0782/10/0100 $10.00

Education
Web Used
for Final
Exams in
Denmark

the government of Denmark says the internet is such an integral part of daily life, it should be included not only in the classroom but in final exams.

Currently 14 colleges in Denmark are piloting a new system of allowing students full access to the internet during exams. All Danish schools are being invited by the government to join the new web-based system by 2011, according to BBC news.

Denmark has been an innovative country in the adaptation and use of new technology, and for more than a decade Danish students have been allowed to use computers to write their exam answers.

“our exams have to reflect daily life in the classroom and daily life in the classroom has to reflect life in society,” said Bertel Haarder, the minister for education. “the internet is indispensable, including in the exam situation. i’m sure that [it] would be a matter of very few years when most european countries will be on the same line.”

BBC news recently reported about Greve High school, one of the pilot schools, located south of Copenhagen, and students’ participation in a Danish language exam. it experts help students set up with their laptops, and CD-RoMs and exam papers are given to the students. standing in the front of the classroom, one of the teachers instructed the students to use any internet site they wanted to answer any of four questions (which focus on a student’s ability to locate and analyze information, not to regurgitate facts and figures), but they could not message each other or email anyone outside of the classroom.

“if we’re going to be a modern school and teach [students] things that are relevant for them in modern life, we have to teach them how to use the internet,” says sanne Yde schmidt, who leads the project at Greve.