Richard Kulpa

Morphology-independent representation of motions for interactive human-like animation

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 a fight training. Hence, each character has to deal with geometric constraints that can change at every time, depending on the opponents’ morphology and gestures.

Realistic following behaviors for crowd simulation

While walking through a crowd, a pedestrian experiences a large number of interactions with his neighbors. The nature of these interactions is varied, and it has been observed that macroscopic phenomena emerge from the combination of these local interactions. Crowd models have hitherto considered collision avoidance as the unique type of interactions between individuals, few have considered walking in groups. By contrast, our paper focuses on interactions due to the following behaviors of pedestrians. Following is frequently observed when people walk in corridors or when they queue. Typical macroscopic stop‐and‐go waves emerge under such traffic conditions. Our contributions are, first, an experimental study on following behaviors, second, a numerical model for simulating such interactions, and third, its calibration, evaluation and applications. Through an experimental approach, we elaborate and calibrate a model from microscopic analysis of real kinematics data collected during experiments. We carefully evaluate our model both at the microscopic and the macroscopic levels. We also demonstrate our approach on applications where following interactions are prominent.

Balancing Deceit and Disguise: How to successfully fool the defender in a 1 vs. 1 situation in rugby

Suddenly changing direction requires a whole body reorientation strategy. In sporting duels such as an attacker vs. a defender in rugby, successful body orientation/reorientation strategies are essential for successful performance. The aim of this study is to examine which biomechanical factors, while taking into account biomechanical constraints, are used by an attacker in a 1 vs. 1 duel in rugby. More specifically we wanted to examine how an attacker tries to deceive the defender yet disguise his intentions by comparing effective deceptive movements (DM(+)), ineffective deceptive movements (DM(-)), and non-deceptive movements (NDM). Eight French amateur expert rugby union players were asked to perform DMs and NDMs in a real 1 vs. 1 duel. For each type of movement (DM(+), DM(-), NDM) different relevant orientation/reorientation parameters, medio-lateral displacement of the center of mass (COM), foot, head, upper trunk, and lower trunk yaw; and upper trunk roll were analyzed and compared. Results showed that COM displacement and lower trunk yaw were minimized during DMs while foot displacement along with head and upper trunk yaw were exaggerated during DMs (DM(+) and DM(-)). This would suggest that the player is using exaggerated body-related information to consciously deceive the defender into thinking he will run in a given direction while minimizing other postural control parameters to disguise a sudden change in posture necessary to modify final running direction. Further analysis of the efficacy of deceptive movements showed how the disguise and deceit strategies needed to be carefully balanced to successfully fool the defender.

Detecting deception in movement: the case of the side-step in rugby

Although coordinated patterns of body movement can be used to communicate action intention, they can also be used to deceive. Often known as deceptive movements, these unpredictable patterns of body movement can give a competitive advantage to an attacker when trying to outwit a defender. In this particular study, we immersed novice and expert rugby players in an interactive virtual rugby environment to understand how the dynamics of deceptive body movement influence a defending player’s decisions about how and when to act. When asked to judge final running direction, expert players who were found to tune into prospective tau-based information specified in the dynamics of ‘honest’ movement signals (Centre of Mass), performed significantly better than novices who tuned into the dynamics of ‘deceptive’ movement signals (upper trunk yaw and out-foot placement) (p<.001). These findings were further corroborated in a second experiment where players were able to move as if to intercept or ‘tackle’ the virtual attacker. An analysis of action responses showed that experts waited significantly longer before initiating movement (p<.001). By waiting longer and picking up more information that would inform about future running direction these experts made significantly fewer errors (p<.05). In this paper we not only present a mathematical model that describes how deception in body-based movement is detected, but we also show how perceptual expertise is manifested in action expertise. We conclude that being able to tune into the ‘honest’ information specifying true running action intention gives a strong competitive advantage.

Mkm: A global framework for animating humans in virtual reality applications

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 these natural laws, 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 users orders. This framework enables VR applications 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.

Fast inverse kinematics and kinetics solver for human-like figures

Applying complex motions to humanoids involves to deal 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 30 Hz on a classical P4 computer

Synchronization for dynamic blending of motions

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.

Cloning crowd motions

This paper introduces a method to clone crowd motion data. Our goal is to efficiently animate large crowds from existing examples of motions of groups of characters by applying an enhanced copy and paste technique on them. Specifically, we address spatial and temporal continuity problems to enable animation of significantly larger crowds than our initial data. We animate many characters from the few examples with no limitation on duration. Moreover, our animation technique answers the needs of real-time applications through a technique of linear complexity. Therefore, it is significantly more efficient than any existing crowd simulation-based technique, and in addition, we ensure a predictable level of realism for animations. We provide virtual population designers and animators with a powerful framework which (i) enables them to clone crowd motion examples while preserving the complexity and the aspect of group motion and (ii) is able to animate large-scale crowds in real-time. Our contribution is the formulation of the cloning problem as a double search problem. Firstly, we search for almost periodic portions of crowd motion data through the available examples. Secondly, we search for almost symmetries between the conditions at the limits of these portions in order to interconnect them. The result of our searches is a set of crowd patches that contain portions of example data that can be used to compose large and endless animations. Through several examples prepared from real crowd motion data, we demonstrate the advantageous properties of our approach as well as identify its potential for future developments.

Motion blending for real-time animation while accounting for the environment

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 to 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 to animate up to one hundred actors in interactive environments

Professional tennis players' serve: correlation between segmental angular momentums and ball velocity

The purpose of the study was to identify the relationships between segmental angular momentum and ball velocity between the following events: ball toss, maximal elbow flexion (MEF), racket lowest point (RLP), maximal shoulder external rotation (MER), and ball impact (BI). Ten tennis players performed serves recorded with a real-time motion capture. Mean angular momentums of the trunk, upper arm, forearm, and the hand-racket were calculated. The anteroposterior axis angular momentum of the trunk was significantly related with ball velocity during the MEF–RLP, RLP–MER, and MER–BI phases. The strongest relationships between the transverse-axis angular momentums and ball velocity followed a proximal-to-distal timing sequence that allows the transfer of angular momentum from the trunk (MEF–RLP and RLP–MER phases) to the upper arm (RLP–MER phase), forearm (RLP–MER and MER–BI phases), and the hand-racket (MER–BI phase). Since sequence is crucial for ball velocity, players should increase angular momentums of the trunk during MEF–MER, upper arm during RLP–MER, forearm during RLP–BI, and the hand-racket during MER–BI.