Main publications of Franck Multon
 |
F. Multon, L. Hoyet, T. Komura and R. Kulpa, IEEE Humanoids'2007
November 2007, to appear
|
 |
F. Multon, L. Hoyet, T. Komura and R. Kulpa, ACM VRST'2007
November 2007, pp77-80
|
 |
F. Multon, R. Kulpa and B. Bideau, Presence: Teleoper. Virtual Environ.
2008, 17(1) (to appear)
|
 |
R. Kulpa, F. Multon and B. Arnaldi, Computer Graphics Forum , Eurographics
2005 special issue
|
 |
R. Kulpa and F. Multon, Proceedings of IEEE Humanoids 2005
|
 |
S. Ménardais, F. Multon, R. Kulpa and B. Arnaldi, Proceedings
of CGI’2004
|
 |
S. Ménardais, R. Kulpa, F. Multon and B. Arnaldi, Proceedings
of ACM SIGGRAPH/Eurographics SCA’04
|
 |
B. Bideau, R. Kulpa, S. Ménardais, L. Fradet, F. Multon, P. Delamarche,
B. Arnaldi, Presence: Teleoper. Virtual Environ. 2003
|
 |
B. Bideau, F. Multon, R. Kulpa, L. Fradet, B. Arnaldi, P. Delamarche,
Neuroscience Letters, 2004
|
 |
G. Nicolas, F. Multon, G. Berillon, F. Marchal, Journal of Biomechanics 40(5):1048-1057
|
Dynamic motion adaptation for 3D acrobatic humanoids
F. Multon, L. Hoyet, T. Komura and R. Kulpa
Abstract
Low-cost dynamics is a key issue in planning complex motions.
This paper aims at proposing a fast algorithm in order to simulate aerial motions for humanoids while using motion capture data.
As the real subject has obviously different anthropometric parameters than the synthetic robot, directly applying motion capture data leads to a non-respect of physical laws.
As a consequence, the humanoid can land in a bad configuration.
During aerial phase, the acceleration of the center of mass may be different from gravity and the angular momentum may change incorrectly.
This so-called retargetting problem is generally addressed in computer animation by solving kinematic constraints.
In this paper, we propose a dynamic filter that is able to rapidly adapt motion in order to preserve its physical correctness.
If the original motion is changed by a user or just replayed on a different skeleton, the filter is about to correct the postures at each time step in less than 2ms in a common computer.
It's consequently possible to change an arm motion during the aerial phase and to immediately check its effect on the global rotation of the humanoid.
Pdf (Not available yet)
Bibtex
<@inproceedings{Multon07c,
author={F. Multon and L. Hoyet and T. Komura and R. Kulpa},
title={Dynamic motion adaptation for 3D acrobatic humanoids},
booktitle={Proceedings of IEEE Humanoids'07},
year={2007},
month={November},
address={Pittsburgh, PA}
}
Interactive control of physically-valid aerial motion: application to VR training system for gymnasts
F. Multon, L. Hoyet, T. Komura and R. Kulpa
Abstract
This paper aims at proposing a new method to animate aerial motions in interactive environments while taking dynamics into account.
Classical approaches are based on spacetime constraints and require a complete knowledge of the motion.
However, in Virtual Reality, the user's actions are unpredictable so that such techniques cannot be used.
In this paper, we deal with the simulation of gymnastic aerial motions in virtual reality.
A user can directly interact with the virtual gymnast thanks to a real-time motion capture system.
The user's arm motions are blended to the original aerial motions in order to verify their consequences on the virtual gymnast's performance.
Hence, a user can select an initial motion, an initial velocity vector, an initial angular momentum, and a virtual character.
Each of these choices has a direct influence on mechanical values such as the linear and angular momentum.
We thus have developed an original method to adapt the character's poses at each time step in order to make these values compatible with mechanical laws: the angular momentum is constant during the aerial phase and the linear one is determined at take-off.
Our method enables to animate up to 16 characters at 30hz on a common PC.
To sum-up, our method enables to solve kinematic constraints, to retarget motion and to correct it to satisfy mechanical laws.
The virtual gymnast application described in this paper is very promising to help sportsmen getting some ideas which postures are better during the aerial phase for better performance.
Bibtex
<@inproceedings{Multon07b,
author={F. Multon and L. Hoyet and T. Komura and R. Kulpa},
title={Interactive control of physically-valid aerial motion: application to VR
training system for gymnasts},
booktitle={Proceedings of ACM Virtual Reality Software and Technology VRST'2007},
year={2007},
month={November},
address={NewportBeach, CA},
pages={77-80}
}
MKM: A global framework for animating humans in virtual
reality applications
F. Multon, R. Kulpa and B. Bideau
Abstract
Virtual humans are more and more used in VR applications but their animation
is still a challenge, especially if complex tasks must be carried-out in interaction
with the user. In many applications with virtual humans, credible virtual characters
play a major role in presence. Motion editing techniques assume that the natural
laws are intrinsically encoded in prerecorded trajectories and that modifications
may preserve them leading to credible autonomous actors. However, a complete
knowledge of all the constraints is required to ensure continuity or to synchronize
and blend several actions necessary to achieve a given task. We propose a framework
capable of performing these tasks in an interactive environment that can change
at each frame, depending on the user's orders. This framework enables to animate
from dozens of characters in real-time for complex constraints to hundreds of
characters if only ground adaptation is performed. It offers the following capabilities:
motion synchronization, blending, retargeting and adaptation thanks to enhanced
inverse kinetics and kinematics solver. To evaluate this framework we have compared
the motor behavior of subjects in real and in virtual environments.
Bibtex
@article{
Multon08,
author={F. Multon and R. Kulpa and B. Bideau},
title={MKM: a global framework for animating humans in virtual reality applications},,
journal={Presence},
volume={17},
year={2008},
month={To appear},
number={1},
}
Morphology-independent representation of motions for interactive
human-like animation
R. Kulpa, F. Multon and B. Arnaldi, Computer Graphics Forum, Eurographics 2005 special issue
Abstract
This paper addresses the problem of human motion encoding for real-time animation in interactive environments. Classically, a motion is stored as a sequence of body postures encoded as a set of joint rotations (quaternions, Euler-like angles or rotation matrices). As a consequence, Cartesian constraints must be solved using inverse kinematics and/or optimization. Those processes involve computation costs that do not allow real-time animation of several characters in interactive environments. To solve such a problem with a minimum computation time, we designed a motion representation independent from the morphology and containing the constraints intrinsically linked to the motion such as feet contacts with the ground. With such a description, a unique motion can be shared by several characters with different morphologies and in different environments. We also adapted a Cyclic Coordinate Descent algorithm that takes advantages of this representation in order to rapidly deal with complex tunable spacetime constraints. For example, this method enables to interactively control at least eight characters with different morphologies that interact each other during fight training. Hence, each character has to deal with geometric constraints that can change at every time, depending on the opponents' morphology and gestures.
Pdf The definitive version is available at www.blackwell-synergy.com
Bibtex
@article{Kulpa05,
author={R. Kulpa and F. Multon and B. Arnaldi},
title={Morphology-independent representation of motions for interactive human-like
animation},
journal={Computer Graphics Forum, Eurographics 2005 special issue},
volume={24},
year={2005},
pages={343-352},
number={3}
}
Fast inverse kinematics and kinetics solver for
human-like figures
R. Kulpa and F. Multon
Abstract
Applying complex motions to humanoids involves dealing with different kinematic, kinetic and dynamic constraints. Although dynamics is more accurate to simulate humanoids, inverse kinematics is an alternative to rapidly calculate plausible movements required for motion planning. Humanoids motion planning that deals with numerous degrees of freedom requires numerous calls to inverse kinematics solvers that make computation time increase significantly. We propose a new approach that is able to solve complex character positioning while dealing with the center of mass position with very few computation time. An iterative hierarchical process is proposed: analytical solutions are proposed for groups of body segments while a higher solver is applied to drive the whole body and is repeated until stability is reached. With such a system, we are able to animate from 22 to 177 characters at 30Hz on a classical P4 computer.
Bibtex
@inproceedings{Kulpa05a,
author={R. Kulpa and F. Multon},
title={fast inverse kinematics and kinetics solver for human-like figures},
booktitle={Proceedings of IEEE Humanoids},
year={2005},
month={december},
address={Tsukuba, Japan},
pages={38-43}
}
Synchronization for dynamic blending of motions
S. Ménardais, R. Kulpa, F. Multon and B. Arnaldi
Abstract
In this paper we present a new real-time synchronization algorithm. In dynamic environments, motions need to be continuously adapted to obtain realistic animations. We propose an advanced time warping algorithm to synchronize such motions. This algorithm uses the sequence of support phases of the motions. It also takes into account the priority associated to each motion. It is based on an algebraic relation to detect incompatible motions and to select elements of the sequence to be enlarged. The resulting time warping function can be non-derivable so it is corrected by using a cardinal spline interpolation. In this paper, we demonstrate that our algorithm always finds at least one solution. This synchronization module is part of a complete animation engine called MKM already used in production.
Bibtex
@inproceedings{Menardais04b,
author={S. Menardais and R. Kulpa and F. Multon and B. Arnaldi},
title={Synchronization for dynamic blending of motions},
booktitle={Proceedings of ACM SIGGRAPH/Eurographics Symposium on Computer Animation},
year={2004},
month={August},
address={Grenoble, France},
pages={325-336}
}
Motion blending for real-time animation while accounting
for the environment
S. Ménardais, F. Multon, R. Kulpa and B. Arnaldi
Abstract
Using motion capture systems to animate humanlike figures still remains difficult when the movements are complex or need to be adapted to geometric constraints. We propose a new method to blend several captured movements while adapting the trajectories to new skeletons and unknown environments. For each body part (considered as resources), a priority is defined for each movement (considered as consumers). The trajectories applied to the skeleton consist of a weighted sum of the motions trajectories. A new technique to compute the weights is proposed. Finally, the system adapts the resulting trajectories to the synthetic skeleton and to the environment. The results enabled us to animate up to a hundred of actors in interactive environments.
Bibtex
@inproceedings{MENARDAIS04,
author={S. M{\'e}nardais and F. Multon and R. Kulpa and B. Arnaldi},
title={Motion blending for real-time animation while accounting for the environment},
booktitle={Computer Graphics International},
year={2004},
month={June},
address={Crete, Greece},
pages={156-159}
}
Real Handball Goalk eeper v s. Virtual Handball Thrower
B. Bideau, R. Kulpa, S. Ménardais, L. Fradet, F. Multon, P. Delamarche, B. Arnaldi
Abstract
Virtual reality offers new tools for human motion understanding. Several applications have been widely used in teleoperation, military training, driving and flying simulators, and so forth. We propose to test if virtual reality is a valid training tool for the game of handball. We focused on the duel between a handball goalkeeper and a thrower. To this end, we defined a pilot experiment divided into two steps: an experiment with real subjects and another one with virtual throwers. The throwers' motions were captured in order to animate their avatar in a reality center. In this paper, we focused on the evaluation of presence when a goalkeeper is confronting these avatars. To this end, we compared the goalkeeper's gestures in the real and in the virtual experiment to determine if virtual reality engendered the same movements for the same throw. Our results show that gestures did not differ between the real and virtual environment. As a consequence, we can say that the virtual environment offered enough realism to initiate natural gestures. Moreover, as in real games, we observed the goalkeeper's anticipation to allow us to use virtual reality in future work as a way to understand the goalkeeper and thrower interactions. The main originality of this work was to measure presence in a sporting application with new evaluation methods based on motion capture.
Bibtex
@article{BIDEAU03,
author={Benoit Bideau and Richard Kulpa and Stephane Menardais and Laetitia
Fradet
and Franck Multon and Paul Delamarche and Bruno Arnaldi},
title={Real handball goalkeeper vs. virtual handball thrower},
journal={Presence: Teleoper. Virtual Environ.},
volume={12},
year={2003},
pages={411--421},
number={4},
publisher={MIT Press},
issn={1054-7460}
}
Using virtual reality to analyze links between handball
thrower kinematics and goalkeeper's reactions
B. Bideau, F. Multon, R. Kulpa, L. Fradet, B. Arnaldi, P. Delamarche
Abstract
This work investigates the design of a new method to evaluate the importance of visual elements taken into account by a handball goalkeeper facing a thrower. Virtual reality was used to design and reproduce standardised situations in a controlled environment. Under such conditions, it was possible to isolate for investigation one visual element in the thrower's gestures. The goalkeeper's movements were recorded in order to compare his reactions to two separate throws where only one visual element was modified. Our systems allowed us to measure and record the effects of small changes in the thrower's movements. With the numerical values we obtained from our results we were able to come up with a scale of significance for each isolated element. These preliminary results look promising for neuroscience, allowing us to better understand the strategies used in duel situations.
Bibtex
@article{BIDEAU04,
author={B. Bideau and F. Multon and R. Kulpa and L. Fradet and B. Arnaldi and
P.
Delamarche},
title={Virtual reality, a new tool to investigate anticipation skills: application
to the goalkeeper and handball thrower duel},
journal={Neuroscience letters},
volume={372},
year={2004},
pages={119-122},
number={1-2}
}
From bone to plausible bipedal locomotion using inverse
kinematics and goalkeeper's reactions
G. Nicolas, F. Multon, G. Berillon, F. Marchal
Abstract
The purpose of this study is to validate a method based on anatomical data and biomechanical locomotor hypotheses that could be applied in palaeontology to simulate locomotion in fossil hominids. The main problem is to ensure that purely mathematical simulation, based on anatomical descriptions, is enough to test hypotheses on human motion control. A 3D geometric model of the lower limb was therefore processed from anatomical descriptions. From this 3D model, we developed a method to retrieve natural lower-limb motion depending on chosen constraints. We assumed that the role of lower-limb motion is to make the feet move from one footprint to the next by following a trajectory that resembles that of living humans (primary task). This method based on inverse kinematics also allows biomechanical laws of bipedal locomotion to be taken into account (secondary tasks). The laws tested in this study relate to preserving joint limits, minimizing energy and minimizing the distance to a rest posture proposed by anthropologists and viewed as input to our system. A weighted sum of the resulting derivable cost functions enabled us to select a specific solution in the null space of the primary task. In order to validate this approach, we compared simulated and captured motion from ten subjects for whom anthropometrical data were recorded. We concluded that this ''anatomically based bipedalism simulation'' seems promising as a means of investigating natural locomotion behaviour and might also be used to retrieve natural locomotion in fossil hominids where only little knowledge is available.
Bibtex
@article{Nicolas06,
author={G. Nicolas and F. Multon and G. Berillon and F. Marchal },
title={From bone to plausible bipedal locomotion using inverse kinematics},
journal={Journal of Biomechanics},
volume={40},
number={5},
pages={1048-1057},
year={2007}
}