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Evolving 3D morphology and behavior by competition
 Proceedings of Artificial Life IV
, 1994
"... This paper describes a system for the evolution and coevolution of virtual creatures that compete in physically simulated threedimensional worlds. Pairs of individuals enter oneonone contests in which they contend to gain control of a common resource. The winners receive higher relative fitness ..."
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Cited by 335 (0 self)
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This paper describes a system for the evolution and coevolution of virtual creatures that compete in physically simulated threedimensional worlds. Pairs of individuals enter oneonone contests in which they contend to gain control of a common resource. The winners receive higher relative fitness scores allowing them to survive and reproduce. Realistic dynamics simulation including gravity, collisions, and friction, restricts the actions to physically plausible behaviors. The morphology of these creatures and the neural systems for controlling their muscle forces are both genetically determined, and the morphology and behavior can adapt to each other as they evolve simultaneously. The genotypes are structured as directed graphs of nodes and connections, and they can efficiently but flexibly describe instructions for the development of creatures ’ bodies and control systems with repeating or recursive components. When simulated evolutions are performed with populations of competing creatures, interesting and diverse strategies and counterstrategies emerge. 1
Evolving Virtual Creatures
 in SIGGRAPH 94 Conference Proceedings, ser. Annual Conference Series
, 1994
"... This paper describes a novel system for creating virtual creatures that move and behave in simulated threedimensional physical worlds. The morphologies of creatures and the neural systems for controlling their muscle forces are both generated automatically using genetic algorithms. Different fitnes ..."
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Cited by 296 (1 self)
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This paper describes a novel system for creating virtual creatures that move and behave in simulated threedimensional physical worlds. The morphologies of creatures and the neural systems for controlling their muscle forces are both generated automatically using genetic algorithms. Different fitness evaluation functions are used to direct simulated evolutions towards specific behaviors such as swimming, walking, jumping, and following. A genetic language is presented that uses nodes and connections as its primitive elements to represent directed graphs, which are used to describe both the morphology and the neural circuitry of these creatures. This genetic language defines a hyperspace containing an indefinite number of possible creatures with behaviors, and when it is searched using optimization techniques, a variety of successful and interesting locomotion strategies emerge, some of which would be difficult to invent or build by design. 1
Curved Surfaces and Coherence for Nonpenetrating Rigid Body Simulation
, 1990
"... A formulation for the contact forces between curved surfaces in resting (noncolliding) contact is presented. In contrast to previous formulations, constraints on the allowable tangential movement between contacting surfaces are not required. Surfaces are restricted to be twicedifferentiable surfac ..."
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Cited by 136 (6 self)
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A formulation for the contact forces between curved surfaces in resting (noncolliding) contact is presented. In contrast to previous formulations, constraints on the allowable tangential movement between contacting surfaces are not required. Surfaces are restricted to be twicedifferentiable surfaces without boundary. Only finitely many contact points between surfaces are allowed; however, the surfaces need not be convex. The formulation yields the contact forces between curved surfaces and polyhedra as well. Algorithms for performing collision detection during simulation on bodies composed of both polyhedra and strictly convex curved surfaces are also presented. The collision detection algorithms exploit the geometric coherence between successive time steps of the simulation to achieve efficient running times.
Lineartime dynamics using lagrange multipliers
 In SIGGRAPH 96 Conference Proceedings, Computer Graphics Proceedings, Annual Conference Series
, 1996
"... Current lineartime simulation methods for articulated figures are based exclusively on reducedcoordinate formulations. This paper describes a general, noniterative lineartime simulation method based instead on Lagrange multipliers. Lagrange multiplier methods are important for computer graphics ..."
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Cited by 101 (0 self)
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Current lineartime simulation methods for articulated figures are based exclusively on reducedcoordinate formulations. This paper describes a general, noniterative lineartime simulation method based instead on Lagrange multipliers. Lagrange multiplier methods are important for computer graphics applications because they bypass the difficult (and often intractable) problem of parameterizing a system’s degrees of freedom. Given a loopfree set of n equality constraints acting between pairs of bodies, the method takes O(n) time to compute the system’s dynamics. The method does not rely on matrix bandwidth, so no assumptions about the constraints’ topology are needed. Bodies need not be rigid, constraints can be of various dimensions, and unlike reducedcoordinate approaches, nonholonomic (e.g. velocitydependent) constraints are allowed. An additional set of k onedimensional constraints which induce loops and/or handle inequalities can be accommodated with cost O(kn). This makes it practical to simulate complicated, closedloop articulated figures with jointlimits and contact at interactive rates. A complete description of a sample implementation is provided in pseudocode. 1
Efficient Synthesis of Physically Valid Human Motion
, 2003
"... Optimization is a promising way to generate new animations from a minimal amount of input data. Physically based optimization techniques, however, are difficult to scale to complex animated characters, in part because evaluating and differentiating physical quantities becomes prohibitively slow. Tra ..."
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Cited by 91 (3 self)
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Optimization is a promising way to generate new animations from a minimal amount of input data. Physically based optimization techniques, however, are difficult to scale to complex animated characters, in part because evaluating and differentiating physical quantities becomes prohibitively slow. Traditional approaches often require optimizing or constraining parameters involving joint torques; obtaining first derivatives for these parameters is generally an O(D²) process, where D is the number of degrees of freedom of the character. In this paper, we describe a set of objective functions and constraints that lead to linear time analytical first derivatives. The surprising finding is that this set includes constraints on physical validity, such as ground contact constraints. Considering only constraints and objective functions that lead to linear time first derivatives results in fast periteration computation times and an optimization problem that appears to scale well to more complex characters. We show that qualities such as squashandstretch that are expected from physically based optimization result from our approach. Our animation system is particularly useful for synthesizing highly dynamic motions, and we show examples of swinging and leaping motions for characters having from 7 to 22 degrees of freedom.
Formulating Dynamic Multirigidbody Contact Problems with Friction as Solvable Linear Complementarity Problems
 NONLINEAR DYNAMICS
, 1997
"... A linear complementarity formulation for dynamic multirigidbody contact problems with Coulomb friction is presented. The formulation, based on explicit Euler integration and polygonal approximation of the friction cone, is guaranteed to have a solution for any number of contacts and contact config ..."
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Cited by 91 (21 self)
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A linear complementarity formulation for dynamic multirigidbody contact problems with Coulomb friction is presented. The formulation, based on explicit Euler integration and polygonal approximation of the friction cone, is guaranteed to have a solution for any number of contacts and contact configuration. A model with the same property is formulated for impact problems with friction and nonzero elasticity coefficient. An explicit Euler scheme based on these formulations is presented and is proved to have uniformly bounded velocities as the stepsize tends to zero for the NewtonEuler formulation in body coordinates.
Coping with Friction for Nonpenetrating Rigid Body Simulation
, 1991
"... Algorithms and computational complexity measures for simulating the motion of contacting bodies with friction are presented. The bodies are restricted to be perfectly rigid bodies that contact at finitely many points. Contact forces between bodies must satisfy the Coulomb model of friction. A tradit ..."
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Cited by 81 (0 self)
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Algorithms and computational complexity measures for simulating the motion of contacting bodies with friction are presented. The bodies are restricted to be perfectly rigid bodies that contact at finitely many points. Contact forces between bodies must satisfy the Coulomb model of friction. A traditional principle of mechanics is that contact forces are impulsive if and only if nonimpulsive contact forces are insufficient to maintain the nonpenetration constraints between bodies. When friction is allowed, it is known that impulsive contact forces can be necessary even in the absence of collisions between bodies. This paper shows that computing contact forces according to this traditional principle is likely to require exponential time. An analysis of this result reveals that the principle for when impulses can occur is too restrictive, and a natural reformulation of the principle is proposed. Using the reformulated principle, an algorithm with expected polynomial time behavior for co...
STRANDS: Interactive Simulation of Thin Solids using Cosserat Models
 EUROGRAPHICS 2002
, 2002
"... STRANDS are thin elastic solids that are visually well approximated as smooth curves, and yet possess essential physical behaviors characteristic of solid objects such as twisting. Common examples in computer graphics include: sutures, catheters, and tendons in surgical simulation; hairs, ropes, a ..."
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Cited by 65 (4 self)
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STRANDS are thin elastic solids that are visually well approximated as smooth curves, and yet possess essential physical behaviors characteristic of solid objects such as twisting. Common examples in computer graphics include: sutures, catheters, and tendons in surgical simulation; hairs, ropes, and vegetation in animation. Physical models based on spring meshes or 3D finite elements for such thin solids are either inaccurate or inefficient for interactive simulation. In this paper we show that models based on the Cosserat theory of elastic rods are very well suited for interactive simulation of these objects. The physical model reduces to a system of spatial ordinary differential equations that can be solved efficiently for typical boundary conditions. The model handles the important geometric nonlinearity due to large changes in shape. We introduce Cosserattype physical models, describe efficient numerical methods for interactive simulation of these models, and implementation results.
The ALIVE System: Wireless, Fullbody Interaction with Autonomous Agents
, 1996
"... The cumbersome nature of wired interfaces often limits the range of application of virtual environments. In this paper we discuss the design and implementation of a novel system, called ALIVE, which allows unencumbered fullbody interaction between a human participant and a rich graphical world i ..."
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Cited by 54 (5 self)
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The cumbersome nature of wired interfaces often limits the range of application of virtual environments. In this paper we discuss the design and implementation of a novel system, called ALIVE, which allows unencumbered fullbody interaction between a human participant and a rich graphical world inhabited by autonomous agents. Based on results obtained with thousands of users, the paper argues that this kind of system can provide more complex and very different experiences than traditional virtual reality systems. The ALIVE system significantly broadens the range of potential applications of virtual reality systems; in particular, the paper discusses novel applications in the area of training and teaching, entertainment, and digital assistants or interface agents. We overview the methods used in the implementation of the exiting ALIVE systems.
A Practical Model for Hair Mutual Interactions
, 2002
"... Hair exhibits strong anisotropic dynamic properties which demand distinct dynamic models for single strands and hairhair interactions. While a single strand can be modeled as a multibody open chain expressed in generalized coordinates, modeling hairhair interactions is a more difficult problem. A ..."
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Cited by 46 (0 self)
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Hair exhibits strong anisotropic dynamic properties which demand distinct dynamic models for single strands and hairhair interactions. While a single strand can be modeled as a multibody open chain expressed in generalized coordinates, modeling hairhair interactions is a more difficult problem. A dynamic model for this purpose is proposed based on a sparse set of guide strands. Long range connections among the strands are modeled as breakable static links formulated as nonreversible positional springs. Dynamic hairtohair collision is solved with the help of auxiliary triangle strips among nearby strands. Adaptive guide strands can be generated and removed on the fly to dynamically control the accuracy of a simulation. A highquality dense hair model can be obtained at the end by transforming and interpolating the sparse guide strands. Fine imagery of the final dense model is rendered by considering both primary scattering and selfshadowing inside the hair volume which is modeled as being partially translucent.