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.