A technique for representing a visual scene as a directed acyclic graph of data and operators that generates a sequence of image frames over specified time intervals. The graph specifies temporal and spatial values for associated visual elements of the scene. Time is modeled in the inheritance properties explicitly defined within the scene graph hierarchy, by assigning temporal attributes to each media element. Branch nodes of the graph specify transforms for the temporal and spatial coordinate systems. To evaluate the appearance or behavior of the scene and in particular the global time values of particular elements at a given time instant, the graph is traversed in a direction from a root node down toward the leaf nodes, thereby causing temporal transformations specified along the branches of the graph to modify time parameters of the scene data at the nodes. Child nodes are preferably evaluated after being transformed, to determine the extent to which they contribute the data to the final scene. Temporal transformations may include translation operations that offset temporal event times; scaling operations that change the rate at which time passes; or clipping operations, that restrict the range of time parameters to exclude the evaluation of parts of the graph.

Time inheritance scene graph for representation of media content

Reference VRLAB-CONF-2007-052View record in Web of Science Record created on 2007-03-05, modified on 2017-05-12

Crowd simulation for interactive virtual environments and VRtraining systems

In this paper we present recent results concerning development of the crowd simulation for interactive virtual environments such as virtual reality training system for urban emergency situations. Our system aims to reproduce realistic scenarios involving large number of the virtual human agents with behaviors based on the behaviors of the real persons in such situations. We define architecture of multi-agent system allowing both scripted and autonomous behaviors of the agents as well as interactions among them, with the virtual environment and with the real human participants.

/pdf/crowd-simulation-for-interactive-virtual-environments-and-vr-52414jwdvo.pdf

Crowd simulation for interactive virtual environments and VR training systems

We present an interactive modeling and animation system that facilitates the integration of a variety of simulation and animation paradigms. This system permits the modeling of diverse objects that change in shape, appearance, and behaviour over time. Our system thus extends modeling tools to include animation controls. Changes can be effected by various methods of control, including scripted, gestural, and behavioral specification. The system is an extensible testbed that supports research in the interaction of disparate control methods embodied in controller objects. This paper discusses some of the issues involved in modeling such interactions and the mechanisms implemented to provide solutions to some of these issues.The system's object-oriented architecture uses delegation hierarchies to let objects change all of their attributes dynamically. Objects include displayable objects, controllers, cameras, lights, renderers, and user interfaces. Techniques used to obtain interactive performance include the use of data-dependency networks, lazy evaluation, and extensive caching to exploit inter- and intra-frame coherency.

/pdf/an-object-oriented-framework-for-the-integration-of-2q0m6k6kj5.pdf

An object-oriented framework for the integration of interactive animation techniques

In this paper, we present research results and future challenges in creating realistic and believable Virtual Humans. To realize these modeling goals, real-time realistic representation is essential, but we also need interactive and perceptive Virtual Humans to populate the Virtual Worlds. Three levels of modeling should be considered to create these believable Virtual Humans: 1) realistic appearance modeling, 2) realistic, smooth and flexible motion modeling, and 3) realistic high-level behaviors modeling. At first, the issues of creating virtual humans with better skeleton and realistic deformable bodies are illustrated. To give a level of believable behavior, challenges are laid on generating on the fly flexible motion and complex behaviours of Virtual Humans inside their environments using a realistic perception of the environment. Interactivity and group behaviours are also important parameters to create believable Virtual Humans which have challenges in creating believable relationship between real and virtual humans based on emotion and personality, and simulating realistic and believable behaviors of groups and crowds. Finally, issues in generating realistic virtual clothed and haired people are presented.

/pdf/virtual-humans-thirty-years-of-research-what-next-3o7fyoz4k1.pdf

Virtual humans: thirty years of research, what next?

In this paper, we present a general, systematic and consistent treatment of time and events for computer animation. We first formalize the concepts of events and create a time primitive called an event unit. We then present a succession of organization schemes to compose event units for generating complex motion sequences. We present a directed graph representation for the organization of time and events that suggests the form of an event-based time programming language. Details of implementation of a general event simulation system are given. Our approach provides a clean partitioning for the problem of motion design, a hierarchical scheme to compose motion behaviors from time primitives and a programming model for organizing animation. Traditional methods of kinematic controls and key frame interpolation are special cases of our general scheme. In addition, our treatment of events can be combined with kinematics, dynamics or constraint-based systems to generate powerful motion modeling systems.

Modeling with Time and Events in Computer Animation

A Constraint-Based Figure-Maker

Constraint-based modeling techniques are emerging as an effective computer graphics approach for modeling and designing objects and their behaviors. In this thesis, computer graphics constraint techniques are unified into a single conceptual framework. The central themes of the thesis are methods to partition an arbitrary constraint problem in different domains and at different levels, and to provide a language and computational environment for modeling with constraints. Using partitioning and composition schemes, complex simulations can be built hierarchically from simpler simulations by "plugging" together separate modules. Fundamental and basic structures are designed and implemented to provide an "Assembly Language" for simulation systems. These structures are put together through a collection of interfaces, much like multiple languages that use the same assembler on a computer. We use strategies called refinement and partitioning to integrate seemingly disparate constraint techniques. We present Temporal Sequencing as an approach to design complex time behaviors of simulation systems. Refinement is a top-down approach of transforming high level representations of a constraint modeling problem into representations that are closer to the basic solution mechanisms available in the constraint environment, such as numerical solution methods. Partitioning is the decomposition of one constraint problem into multiple simpler constraint problems that are then studied separately. Temporal Sequencing is a methodology to design the time behavior of a simulation system by composing time behaviors of the system over subintervals of time. Using the above partitioning schemes for the solution and specification of a general constraint problem, we create a unified constraint environment with the capability to both solve constraint problem instances and to create specialized constraint systems. New methods of constraint specification and solution can be added into the same constraint framework as new methods are developed. Based on the above approach, a modeling system called "Our Constraint Environment" (OCE) has been implemented. A programming language as an extension to C++ has been designed to provide an interface to OCE. The language provides the constructs for the partitioning schemes discussed above. Simulations created using OCE have shown the efficacy of our design approach. Constraint-based modeling techniques are emerging as an effective computer graphics approach for modeling and designing objects and their behaviors. In this thesis, computer graphics constraint techniques are unified into a single conceptual framework. The central themes of the thesis are methods to partition an arbitrary constraint problem in different domains and at different levels, and to provide a language and computational environment for modeling with constraints. Using partitioning and composition schemes, complex simulations can be built hierarchically from simpler simula

/pdf/a-unified-framework-for-constraint-based-modeling-2pjgqw508e.pdf

A unified framework for constraint-based modeling

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Modeling with Time and Events in Computer Animation

A Constraint-Based Figure-Maker

A unified framework for constraint-based modeling