Multitouch Motion Capturing - Digital Media Lab

Multitouch Motion Capturing
Markus Krause
[email protected]
Marc Herrlich
[email protected]
Lasse Schwarten
[email protected]
Jens Teichert
[email protected]
Benjamin Walther Franks
[email protected]
Digital Media Group, TZI, University of Bremen
Abstract
2. Related Work
Full body motion capturing is a well known approach
for animating virtual characters. A detailed description of
the capabilities and limitations of motion capturing systems
can be found in the PhD thesis of Ann Pullen [6]. Aside
full body motion capturing systems many other techniques
where described to adapt human motions to virtual characters. Some of these techniques summarized as puppetry
were described by Sturman [7]. An animation technique
using a graphic tablet and two pens to sketch out character footsteps was shown by Kohlhoff et al. [2]. Laszlo et
al. [4] announced a technique to control animations or aspects of physical simulations by using pointing devices like
a mouse. In the context of multitouch systems Moscovich
[5] presented a method to animate two dimensional shapes
as well as a simple skeletal animation framework and a 3D
animation tool.
Convincing animations of virtual characters continue to
require motion capture technology or extensive skills in
manual keyframing. We want to outline a simple yet natural motion capturing method that takes advantage of multitouch input devices to create believable character motion.
1. Introduction
The most fundamental animation technique keyframing
is far less complex then motion capturing but needs skilled
animators. As stated out by Terra and Metoyer [8] a key
problem for novice animators in keyframing is timing of
motion. Another problem as we surveyed on our own is
animation continuity. In the real world almost all action
moves in an arc. Creating a motion along a curved path
is sometimes difficult in keyframed animation. Both problems were described in detail by Lasseter [3]. Motion capture aids animators in the task of making virtual characters
move in realistic ways by enabling movement data to be
recorded from observation of an actor performing the desired motions. These techniques overcome the problems of
animation continuity and timing but are often expensive or
may require lots of space and setup. In our approach we outline a simple but yet natural and powerful motion capturing
method using multitouch capable input devices.
3. Surface Motion Capturing
An advantage of multitouch capable input devices is
tracking multiple degrees of freedom simultaneously. One
could for example track the position of one finger to control two components of an objects position and one finger to
control the third component. The problem in doing so is that
dependencies of object motion and finger movement are not
intuitively understandable for the animator. A quiet similar
problem occurs on modifying movement and time simultaneously. A more intuitive method should allow to modify
1
Figure 1. Captured animation of a bouncing ball
only those degrees of freedom visible to the animator. Such
a method could track the users finger over time taking sample points at discreet time intervals and calculating a simplified curve out of these points. This curve projected onto
an animation plane parallel to the viewing plane defines the
object motion path as shown in figure 2. The vertices of
this path should contain all information about the objects
transformation through time so that not captured degrees of
freedom can later be defined by the animator if necessary.
By using simple metaphors depending on multiple fingers
one could easily animate additional degrees of freedom as
shown in figure 1. Capturing movements of a human body
in this way compared to traditional keframe animation reduces the problem of animation continuity quiet well. The
problem of timing on the other hand is still not solved appropriately by this method. To handle this problem we use
a technique from Terra and Metoyer [8]. These method allows to sketch out timing of motion without changing the
animation path itself.
Figure 2. Motion path
4. Applying Motion Data to Bone Structures
Applying the described method to an object within a inverse kinematics allows intuitive animation of skeletons as
shown in the figure of the first page. Even complex hand
gestures could be applied to skeletons to animate realistic
hand movement. A different approach could use captured
data to control a physical simulation of a skeleton as described by Laszlo et al. [4]. In conjunction to skeletal animation also gait animations become important. Kohlhoff et
al. [2] describes a technique for creating footsteps for those
gait animations using a multitouch capable graphics tablet.
In contrast to full body motion capturing our technique is
not always able to capture a skeletal animation in a single
pass. To handle this it has to be possible to capture different features of an animation separately and composite them
later on. Dontcheva et al. [1] present a method for layering
animations by composing feature animations of a character
and instantly reflecting the resulting animation to the animator.
5. Conclusion
We outlined a multitouch based animation paradigm that
helps to overcome the described issues of animation continuity and timing. The next steps are clearly to fully implement this system on a multitouch table and to verify the
expected effects.
References
[1] M. Dontcheva, G. Yngve, and Z. Popović. Layered acting
for character animation. ACM Trans. Graph., 22(3):409–416,
2003.
[2] P. Kolhoff, J. Preuß, and J. Loviscach. Walking with pens. In
Eurographics 2005 Short Presentations, pages 33–36, 2005.
[3] J. Lasseter. Principles of traditional animation applied to 3d
computer animation. SIGGRAPH Comput. Graph., 21(4):35–
44, 1987.
[4] J. Laszlo, M. van de Panne, and E. Fiume. Interactive control
for physically-based animation. In SIGGRAPH ’00: Proceedings of the 27th annual conference on Computer graphics and
interactive techniques, pages 201–208, New York, NY, USA,
2000. ACM Press/Addison-Wesley Publishing Co.
[5] T. Moscovich. Principles and applications of multi-touch interaction. PhD thesis, Providence, RI, USA, 2007. AdviserJohn F. Hughes.
[6] K. A. Pullen. Motion capture assisted animation: texturing and synthesis. PhD thesis, Stanford, CA, USA, 2002.
Adviser-Christoph Bregler.
[7] D. J. Sturman. Computer puppetry. IEEE Comput. Graph.
Appl., 18(1):38–45, 1998.
[8] S. C. L. Terra and R. A. Metoyer. Performance timing for
keyframe animation. In SCA ’04: Proceedings of the 2004
ACM SIGGRAPH/Eurographics symposium on Computer animation, pages 253–258, Aire-la-Ville, Switzerland, Switzerland, 2004. Eurographics Association.