The sketching interface is emerging as an alternative modeling method. Users draw 2D lines on the screen;
the system then generates a 3D model automatically, inferring missing
depth information. Sketching interfaces for 3D scenes consisting of simple primitives were first introduced in
the SKETCH system, 18 allowing users
to perform complicated 3D editing
operations in a single camera view by
combining heuristics. A similar approach is used in commercial systems
(such as Google’s SketchUp). However, these systems are designed for
sketching simple shapes defined by
relatively few parameters. Designing
them requires specialized training.
Our group at the University of Tokyo
developed the Teddy system11 to address
this problem, allowing users to quickly
generate interesting 3D freeform models (such as creating a teddy bear by
drawing the silhouette of the desired
shape) (see Figure 1). The user’s strokes
are in red; the system infers and draws
everything else. The user first draws the
silhouette of the base primitive, and the
system generates the corresponding 3D
geometry. The user then draws a stroke
across the model, and the system cuts
the model at the line. The user can also
add parts to the base model by drawing
two strokes; Figure 2 shows several 3D
models created this way.
We do not expect Teddy to replace
traditional 3D modeling tools. Rather,
it will create new 3D modeling applications that are useful to nonexperts, including children, who want to play with
3D graphics for fun. Introduced at the
SIGGRAPH conference in 1999, Teddy
is used in several current commercial
video games to permit players to create
their own characters. Using it is a useful way for experts to express their ideas
quickly in early design phases. A commercial 3D modeling package, Shade
(available only in Japan, http://shade.e-frontier.co.jp/), includes an extension to
Teddy as a plug-in for generating rough
sketches. Finally, and most important,
Teddy is useful for communicating 3D
concepts face to face. In a classroom, for
example, a teacher could quickly draw a
model of bacteria, showing its cross section to explain its internal structure. In
a hospital, a medical doctor could draw
a model of a stomach to help explain a
patient’s stomach disease.
In 2003, to test the idea, we conducted a trial in a high school geography
class in Chiba, Japan. Teaching 3D concepts (such as mountains and valleys),
a geography teacher would have difficulty explaining them using traditional
2D media like a blackboard. Sketching
in 3D can help address this problem.
A convincing example is the teaching
of contour lines using the Teddy system (see Figure 3) in which the teacher
first shows a 3D model of a mountain,
then draws several horizontal lines in
the side view, saying the lines indicate
equal height intervals. The teacher
then changes the viewpoint to show
the mountain and the lines from the
top. This way, students understand the
relationship between the closed lines
on the map (contour lines) and the 3D
geography, not just mountains, ridges,
and valleys.
clothing manipulation
3D characters must also be dressed
properly. The computer-graphics re-
search community has actively in-
vestigated the physical simulation of
cloth, today producing realistic cloth
simulations. However, the initial sim-
ulated-cloth configuration must be
set manually, and the user interface
for manipulating cloth is primitive. A
typical approach is to place rigid cloth
patches around the target body, com-
bining 3D translation and rotation be-
fore starting the simulation—a tedious
process. Moreover, users have difficulty
changing the way the garment is worn
once they’ve placed it on a character.
Standard systems allow users to freely
move individual vertices through direct
manipulation, but it causes a large local
distortion (stretching), making it diffi-
cult to achieve global movement.
figure 4. users draw marks on the character and cloth; the system then places the cloth on
the character.
figure 5. Dragging the cloth onto the character: left, before dragging; center, the result of
traditional vertex dragging; right, the result of our clothing-manipulation method.