Computer Animation and Simulation ’96

Consider the following problem: A viewpoint moves amongst a set of line segments in the plane and it is desired to maintain the sequence of lines visible from the viewpoint at every increment in its position. The sequence of visible lines is identical for most increments in the position of the viewpoint. It is different only when the viewpoint crosses a visual discontinuity line. Our objective is to be able to quickly report whether the sequence of visible lines needs to be updated and perform the update quickly in that case. We propose an algorithm that satisfies both criteria while using space linear in the number of visual discontinuity lines. This last condition is important because constructing the arrangement of these lines would take space quadratic in their number.

this paper describes an improvement of the self-organizing feature map (SOFM) obtained with the Kohonen neural network. The ameliorations are dedicated to its usage in computer graphics and mainly in animation of particle-based systems. We show its application in the context of the visualization of molecular dynamic systems. Comparison with other works based on particle systems is then made. Finally, we propose some possible extensions to this work.

Mass/Spring networks are commonly used to produce simulations of deformable bodies for computer animation. However, such an approach can produce inaccurate results if too coarse a discretisation is employed, and so many animators use excessively large (and slow) networks. In order to remove the ‘guesswork’ from such an approach this paper presents a mechanism for adaptively refining portions of such systems to a required accuracy, thereby producing more pleasing results at a reduced computational cost. Following a discussion of the use of such an approach in simulating a deformable sheet, we present several characteristic examples to demonstrate its suitability.

In this paper we present a model for fire in 2-D animation. Here the emphasis is on a stylistic representation of fires and the flames which arise from the bodies of such fires. We show how to devise a skeleton framework for generating animation sequences which match the hand-drawn series, and in particular how to match the flame orientations, shapes, and the connection curves, as required by the simulated style, between them. The parameters associated with these skeletons, flame types and connection curves are brought together into a matrix tableau for the particular representation of the fire base in the model. The model for the flames at the top of the fire are made up from of three simple sub-models. By stochastically varying the parameters the model can generate plausible looking sequences of animated fire and include the effects of wind straightforwardly.

This paper presents a new formalism for simulating highly deformable bodies with a particle system. Smoothed particles represent sample points that enable the approximation of the values and derivatives of local physical quantities inside a medium. They ensure valid and stable simulation of state equations that describe the physical behavior of the material.

We extend the initial formalism, first introduced for simulating cosmological fluids, to the animation of inelastic bodies with a wide range of stiffness and viscosity. We show that the smoothed particles paradigm leads to a coherent definition of the object’s surface as an iso-surface of the mass density function. Implementation issues are discussed, including an efficient integration scheme using individually adapted time steps to integrate particle motion. Animation requires a linear complexity in the number of particles, offering reasonable time and memory use.

There are many possible ways of identifying the posture of a human character from a set of known positions. These methods differ in subtle but important ways. We propose an alternative method to the jacobian-based Inverse Kinematics, one which allows for simple calibration, allows for sensors slippage, and can take advantage of knowledge of the type of motion being performed. This approach gives real-time conversion of magnetic sensors measurements into human anatomical rotations. Our converter is used in a wide range of applications from real time applications to animation design. It provides a useful complement to the traditional keyframe editing software.

This paper describes a locomotion control technique for articulated figures in which new movements are interactively generated from a set of reference movements. Reference movements based on walking and running gait patterns are used to form a locomotion framework. An animator interactively specifies an envisioned movement as an interpolation between these reference movements by drawing a path within the locomotion framework and by traversing the path to produce a temporal mapping (or by applying a predefined temporal mapping). The result is a high-level locomotion control mechanism that supports real-time creation of new movements from an existing movement base.

This paper presents an optimization based technique for solving optimal control problems. Unlike the spacetime constraint approach which discretizes both the state and control variables, our method transforms the optimal control problem into an optimization task that depends only upon the control variables. Using a spline to represent the control trajectory, we derive an efficient, analytic technique for computing the gradient of the objective function in terms of the spline control points. Our approach has the advantage of reducing the number of unknowns and ensuring consistency between the state and control variables. We demonstrate the viability of our algorithm by using it to simulate a human figure performing a high jump.

In this paper, we provide the biomechanical model of human upper limb we have designed and applied to the three-dimensional left human arm reconstructed from the Visible Human imaging Dataset. This model includes the mechanical properties for bones, joints and muscles lines of action. This work has been done as a part of the European Esprit Project CHARM. Its objective is to develop a Comprehensive Human Animation Resource Model allowing the dynamic simulation of complex musculoskeletal systems, including finite element deformation of soft-tissues and muscular contraction. In our approach, simplifications have been done so as to ensure the feasibility of the project while preserving the biomechanical validity of the model.

We present a method for interactive modelling and animation of natural branching structures such as plants. Objects are created according to a rule based description. Geometric information is encapsulated in the objects and can be edited by methods such as free form deformation and spline techniques. Global and partial constraints allow the modelling of specific plants. The rule system is represented by a structure tree with components of high functionality, that can be edited graphically. Keyframe techniques are applicable and allow to simulate parts of the models with local time. In comparison to other rulebased approaches, complex branching structures can be developed faster and more flexible.

During a simulation of plant development evaluation of the amount of light plays a significant role. Most of the previous works take into account only constant amount and constant direction of the light in the scene without respect to local shadows in the tree. In the other works this evaluation strongly depends on the number of objects in the scene.

This paper introduces a new method for evaluation of amount of light for the artificial plants. This technique is based on Z-buffer algorithm and has the ability to evaluate the direction and the amount of light for every leaf in the plant with a significantly decreased time of calculation. Several new aspects of lifetime of the plant elements and of the whole plant are discussed.

Motions such as flips and jumps are challenging to animate and to perform in real life. The difficulty arises from the dynamic nature of the movements and the precise timing required for their successful execution. This paper presents a decision-tree search algorithm for planning the control for these types of motion. Several types of results are presented, including cartwheels, flips and hops for a two-link gymnastic ‘acrobot’. It is also shown that the same search algorithm is effective at a macroscopic scale for planning dynamic motions across rugged terrain.

Accuracy is the ubiquitous goal of dynamic simulation, in order to yield the “correct” motion. But for creating animation, what is really of interest is “plausible” motion, which is somewhat different. We discuss what we mean by plausible simulation, how it differs from “accurate” simulation, and why we think it’s a worthwhile area to study. The discussion touches on questions of physically plausible vs. visually plausible motion, plausible simulation in a noisy or textured environment, and probability measures for motion, as well as issues for forward and inverse problems.

A technique is proposed for creating new animations from a set of representative example motions stored in a motion database. Animations are created by cutting-and-pasting together the example motion segments as required. Motion segments are selected based upon how well they fit into a desired motion and are then automatically tailored for a precise fit. Various fundamental problems associated with the use of motion databases are outlined. A prototype implementation is used to validate the proposed concepts and to explore possible solutions to the aforementioned problems.