3-D interior modeling: A virtual walk on the inside
BERKELEY, Calif. – A laser-equipped backpack worn by a human
operator has provided 3-D modeling of interior sections of a campus building at
the University of California, enabling a virtual walk through the academic halls.
Automated 3-D modeling of building interiors has possible virtual
reality applications in entertainment, gaming, architecture, building energy management
systems and even military reconnaissance. The technique of “virtualizing”
interiors also could have applications in documenting historical sites, mapping
hazardous areas and preparing for disaster management.
“Traditional indoor mapping systems are on wheeled robots
or pushcarts which work on planar surfaces,” said Avideh Zakhor, a professor
and lead researcher for the project at the university’s video and image processing
There are distinct disadvantages to such systems, she added. “A
human operator can ensure that all objects of interest within an indoor environment
are properly captured. Today, a robot cannot offer that. Another important technological
innovation is to localize in the absence of GPS signals. In outdoor modeling, GPS
can readily be used to recover pose. For indoors, the GPS signal does not penetrate
inside buildings and, therefore, other techniques have to be developed for indoor
Also, traditional indoor mapping systems recover only three degrees
of freedom of movement: X, Y and yaw, Zakhor noted. “The ability to model
complex environments such as staircases or uneven surfaces was one of our motivations
at the outset, to come up with a human-operated backpack system, rather than a wheeled
robot: A robot cannot do staircases, but a human operator can.”
A laser-equipped backpack for virtualizing building interiors is carried by a human operator. Images
courtesy of VIP Lab, University of California, Berkeley.
The most important technological advances in the research thus
far are automatic sensor fusion algorithms that localize the backpack accurately
and that build texture-mapped 3-D models, she said. “These models can then
be rendered for interactive virtual walkthroughs or ‘flythroughs’ of
indoor environments. The localization is particularly difficult, since we need to
recover six degrees of freedom of movement – that is, X, Y, Z, yaw, pitch
The backpack apparatus includes a number of laser scanners and
cameras and one inertial orientation measurement system (OMS). “In essence,
the laser scanners serve a dual purpose,” Zakhor said. The scans from the
2-D laser scanners are used to localize the backpack by matching successive horizontal
scans to recover yaw and successive vertical scans to recover roll or pitch. In
addition, once the backpack is localized, the scans are used to create a 3-D point
cloud of the environment, which is essentially the 3-D geometry.
Shown is a model of hallways located on two floors of a building on the University of
California, Berkeley, campus. The data for the model was captured in a single run
with the laser backpack, using a stairwell to move between floors.
The camera imagery is used to texture-map the resulting 3-D models.
It serves a dual purpose in that it is used to refine and reduce localization errors,
Zakhor said. “In particular, camera imagery is used to automatically detect
‘loop closures’ – that is, places that the backpack has visited
before. It turns out that such detections can be successfully used to drastically
reduce the localization error due to laser scan matching and the OMS.”
The laser scanners and cameras and OMS are all fused via a number
of algorithms to localize the backpack, she said. “Once the backpack is localized,
we can stack the vertical laser scans together to generate a point cloud, which
is then texture-mapped using cameras.”
The backpack has three orthogonally mounted laser scanners. “We
apply scan matching algorithms to successive scans from each scanner to recover
two translation and one rotation parameter,” she said. “For example,
by applying scan matching to the horizontal scanner, we recover X, Y and yaw. Ditto
for the two vertical scanners: One is used to recover X, Z and pitch, and the other,
Y, Z and roll. We then combine these to recover all six degrees of freedom; that
is, X, Y, Z, yaw, pitch and roll.”
The researchers are working constantly to improve the error performance
of this system, which translates directly into more accurate localization and better-looking
“My guess is that it has to be tested a lot more extensively
in more buildings before it can be put into use on a routine basis for military
missions,” Zakhor said, adding that they also should and can streamline the
overall system both algorithmically and architecturally.
“We have too many sensors and too many algorithms in action
now. We need to systematically analyze to see which one of the many sensors we can
discard without affecting the overall performance of the system,” she said.
She noted that rendering and visualization of the models are important
considerations. “Our models are so detailed that commercial viewers are not
able to render them in full detail. As such, we either have to develop simplification
algorithms to make them work with existing off-the-shelf rendering algorithms or
need to do our own custom-made renderers. Without rendering capability, it is impossible
to interact and visualize the models we have worked hard to generate.”
A paper by Zakhor and her team, titled “Indoor Localization
and Visualization Using a Human-Operated Backpack System,” was presented at
the 2010 International Conference on Indoor Positioning and Indoor Navigation in
September in Zürich, Switzerland.
Research leading to the development of the laser backpack for
military applications was funded by the US Air Force Office of Scientific Research
(AOFSR) in Arlington, Va., and the US Army Research Office in Durham, N.C. The backpack
could enable military personnel to view a virtual building interior collectively
and to interact over a network to achieve goals such as mission planning, according
to an AOFSR press release.