Interactive skeleton-driven simulation
Encyclopedia
Interactive skeleton-driven simulation (or Interactive skeleton-driven dynamic deformations) is a scientific computer simulation
technique used to approximate realistic physical deformations of dynamic bodies in real-time
. It involves using elastic
dynamics
and mathematical optimization
s to decide the body-shapes during motion and interaction with force
s. It has various applications within realistic simulations for medicine
, 3D computer animation
and virtual reality
.
is well known in computer animation
and 3D character simulation. Because of the calculation intensitivity of the simulation, few interactive systems are available which realistically can simulate dynamic bodies in real-time
. Being able to interact with such a realistic
3D model would mean that calculations would have to be performed within the constraints of a frame rate
which would be acceptable via a user interface
.
Recent research has been able to build on previously developed models and methods to provide sufficiently efficient and realistic simulations. The promise for this technique can be as widespread as mimic
ing human facial expression
s for perception
of simulating a human actor in real-time or other cell
organism
s. Using skeletal constraints and parameterized force to calculate deformations also has the benefit of matching how a single cell has a shaping skeleton
, as well as how a larger living organism might have an internal bone skeleton - such as the vertebraes. The generalized external body force simulations makes elasticity
calculations more efficient, and means real-time interaction
s are possible.
domain with calculations of these hierarchical functions similar to that of lazy
wavelet
s
Rather than fitting the object to the skeleton, as is common, the skeleton is used to set constraints for deformation. Also the hierarchical basis means that detail levels can be introduced or removed when needed - for example, observing from a distance or hidden surfaces.
Pre-calculated pose
s are used to be able to interpolate between shapes and achieve realistic deformations throughout motions. This means traditional keyframes are avoided.
There are performance tuning
similarities between this technique and procedural generation
, wavelet
and data compression
methods.
Start by defining the object you wish to animate as a set (ie define all the points):
.
Then get a handle on it.
Let
Then you need to define the rest state of the object (the non-wobble point):
, with available reference of details. Academic institutions and commercial enterprises like Alias Systems Corporation
(the makers of the Maya
rendering software), Intel and Electronic Arts
are among the known proponents of this work. There are also videos available showcasing the techniques, with editors showing interactivity in real-time with realistic results. The computer game Spore
also has showcased similar techniques.
Computer simulation
A computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...
technique used to approximate realistic physical deformations of dynamic bodies in real-time
Real-time computing
In computer science, real-time computing , or reactive computing, is the study of hardware and software systems that are subject to a "real-time constraint"— e.g. operational deadlines from event to system response. Real-time programs must guarantee response within strict time constraints...
. It involves using elastic
Elasticity (physics)
In physics, elasticity is the physical property of a material that returns to its original shape after the stress that made it deform or distort is removed. The relative amount of deformation is called the strain....
dynamics
Dynamics (mechanics)
In the field of physics, the study of the causes of motion and changes in motion is dynamics. In other words the study of forces and why objects are in motion. Dynamics includes the study of the effect of torques on motion...
and mathematical optimization
Optimization (mathematics)
In mathematics, computational science, or management science, mathematical optimization refers to the selection of a best element from some set of available alternatives....
s to decide the body-shapes during motion and interaction with force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
s. It has various applications within realistic simulations for medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, 3D computer animation
Computer animation
Computer animation is the process used for generating animated images by using computer graphics. The more general term computer generated imagery encompasses both static scenes and dynamic images, while computer animation only refers to moving images....
and virtual reality
Virtual reality
Virtual reality , also known as virtuality, is a term that applies to computer-simulated environments that can simulate physical presence in places in the real world, as well as in imaginary worlds...
.
Background
Methods for simulating deformation, such as changes of shapes, of dynamic bodies involve intensive calculations, and several models have been developed. Some of these are known as free-form deformation, skeleton-driven deformation, dynamic deformation and anatomical modelling. Skeletal animationSkeletal animation
Skeletal animation is a technique in computer animation in which a character is represented in two parts: a surface representation used to draw the character and a hierarchical set of interconnected bones used to animate the mesh...
is well known in computer animation
Computer animation
Computer animation is the process used for generating animated images by using computer graphics. The more general term computer generated imagery encompasses both static scenes and dynamic images, while computer animation only refers to moving images....
and 3D character simulation. Because of the calculation intensitivity of the simulation, few interactive systems are available which realistically can simulate dynamic bodies in real-time
Real-time computing
In computer science, real-time computing , or reactive computing, is the study of hardware and software systems that are subject to a "real-time constraint"— e.g. operational deadlines from event to system response. Real-time programs must guarantee response within strict time constraints...
. Being able to interact with such a realistic
Realistic
Realistic may refer to:*Realism *Realistic , a former RadioShack brand used to market audio electronics...
3D model would mean that calculations would have to be performed within the constraints of a frame rate
Frame rate
Frame rate is the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems...
which would be acceptable via a user interface
User interface
The user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the...
.
Recent research has been able to build on previously developed models and methods to provide sufficiently efficient and realistic simulations. The promise for this technique can be as widespread as mimic
Mimic
In evolutionary biology, mimicry is the similarity of one species to another which protects one or both. This similarity can be in appearance, behaviour, sound, scent and even location, with the mimics found in similar places to their models....
ing human facial expression
Facial expression
A facial expression one or more motions or positions of the muscles in the skin. These movements convey the emotional state of the individual to observers. Facial expressions are a form of nonverbal communication. They are a primary means of conveying social information among humans, but also occur...
s for perception
Face perception
Face perception is the process by which the brain and mind understand and interpret the face, particularly the human face.The human face's proportions and expressions are important to identify origin, emotional tendencies, health qualities, and some social information. From birth, faces are...
of simulating a human actor in real-time or other cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s. Using skeletal constraints and parameterized force to calculate deformations also has the benefit of matching how a single cell has a shaping skeleton
Skeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
, as well as how a larger living organism might have an internal bone skeleton - such as the vertebraes. The generalized external body force simulations makes elasticity
Elasticity (physics)
In physics, elasticity is the physical property of a material that returns to its original shape after the stress that made it deform or distort is removed. The relative amount of deformation is called the strain....
calculations more efficient, and means real-time interaction
Interaction
Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way causal effect...
s are possible.
Basic theory
There are several components to such a simulation system:- a polygon meshPolygon meshA polygon mesh or unstructured grid is a collection of vertices, edges and faces that defines the shape of a polyhedral object in 3D computer graphics and solid modeling...
defining the body shape of the model - a coarse volumetric mesh using finite element methodFinite element methodThe finite element method is a numerical technique for finding approximate solutions of partial differential equations as well as integral equations...
s to ensure complete integration over the model - line constraints corresponding to internal skeleton and instrumented to the model
- linearLinearIn mathematics, a linear map or function f is a function which satisfies the following two properties:* Additivity : f = f + f...
izing of equations of motion to achieve interactive rates - hierarchical regions of the mesh associated with skeletal lines
- blending of locally linearlized simulations
- a control lattice through subdivision fitting the model by surrounding and covering it
- a hierarchical basis containing functions which will provide values for deformation of each lattice
domain with calculations of these hierarchical functions similar to that of lazy
Lazy evaluation
In programming language theory, lazy evaluation or call-by-need is an evaluation strategy which delays the evaluation of an expression until the value of this is actually required and which also avoids repeated evaluations...
wavelet
Wavelet
A wavelet is a wave-like oscillation with an amplitude that starts out at zero, increases, and then decreases back to zero. It can typically be visualized as a "brief oscillation" like one might see recorded by a seismograph or heart monitor. Generally, wavelets are purposefully crafted to have...
s
Rather than fitting the object to the skeleton, as is common, the skeleton is used to set constraints for deformation. Also the hierarchical basis means that detail levels can be introduced or removed when needed - for example, observing from a distance or hidden surfaces.
Pre-calculated pose
Pose
"Pose" is the first single by Puerto Rico reggaeton artist Daddy Yankee from the movie soundtrack to the motion picture Talento de Barrio, and was released on May 14, 2008, by Machete Music and El Cartel Records. The single was made available through online music stores on August 12, 2008...
s are used to be able to interpolate between shapes and achieve realistic deformations throughout motions. This means traditional keyframes are avoided.
There are performance tuning
Performance tuning
Performance tuning is the improvement of system performance. This is typically a computer application, but the same methods can be applied to economic markets, bureaucracies or other complex systems. The motivation for such activity is called a performance problem, which can be real or anticipated....
similarities between this technique and procedural generation
Procedural generation
Procedural generation is a widely used term in the production of media; it refers to content generated algorithmically rather than manually. Often, this means creating content on the fly rather than prior to distribution...
, wavelet
Wavelet
A wavelet is a wave-like oscillation with an amplitude that starts out at zero, increases, and then decreases back to zero. It can typically be visualized as a "brief oscillation" like one might see recorded by a seismograph or heart monitor. Generally, wavelets are purposefully crafted to have...
and data compression
Data compression
In computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....
methods.
Algorithmic considerations
To achieve interactivity there are several optimizations necessary which are implementation specific.Start by defining the object you wish to animate as a set (ie define all the points):
.Then get a handle on it.
Let
Then you need to define the rest state of the object (the non-wobble point):
Projects
Projects are taking place to further develop this technique and presenting results to SIGGRAPHSIGGRAPH
SIGGRAPH is the name of the annual conference on computer graphics convened by the ACM SIGGRAPH organization. The first SIGGRAPH conference was in 1974. The conference is attended by tens of thousands of computer professionals...
, with available reference of details. Academic institutions and commercial enterprises like Alias Systems Corporation
Alias Systems Corporation
Alias Systems Corporation , headquartered in Toronto, Ontario, Canada, was a software company that produced high-end 3D graphics software. The company was formed in 1995 when Silicon Graphics bought Alias Research, which was founded in 1983, and Wavefront Technologies, founded in 1984, then merged...
(the makers of the Maya
Maya (software)
Autodesk Maya , commonly shortened to Maya, is 3D computer graphics software that runs on Microsoft Windows, Mac OS and Linux, originally developed by Alias Systems Corporation and currently owned and developed by Autodesk, Inc. It is used to create interactive 3D applications, including video...
rendering software), Intel and Electronic Arts
Electronic Arts
Electronic Arts, Inc. is a major American developer, marketer, publisher and distributor of video games. Founded and incorporated on May 28, 1982 by Trip Hawkins, the company was a pioneer of the early home computer games industry and was notable for promoting the designers and programmers...
are among the known proponents of this work. There are also videos available showcasing the techniques, with editors showing interactivity in real-time with realistic results. The computer game Spore
Spore (2008 video game)
Spore is a multi-genre single-player god game developed by Maxis and designed by Will Wright. The game was released for the Microsoft Windows and Macintosh operating systems in September 2008 as Spore...
also has showcased similar techniques.
See also
- KinematicsKinematicsKinematics is the branch of classical mechanics that describes the motion of bodies and systems without consideration of the forces that cause the motion....
- DynamicsDynamics (mechanics)In the field of physics, the study of the causes of motion and changes in motion is dynamics. In other words the study of forces and why objects are in motion. Dynamics includes the study of the effect of torques on motion...
- Computer animationComputer animationComputer animation is the process used for generating animated images by using computer graphics. The more general term computer generated imagery encompasses both static scenes and dynamic images, while computer animation only refers to moving images....
- Skeletal animationSkeletal animationSkeletal animation is a technique in computer animation in which a character is represented in two parts: a surface representation used to draw the character and a hierarchical set of interconnected bones used to animate the mesh...
- Morph target animationMorph target animationMorph target animation, per-vertex animation, shape interpolation, or blend shapes is a method of 3D computer animation used together with techniques such as skeletal animation. In a morph target animation, a "deformed" version of a mesh is stored as a series of vertex positions...
- 3D computer graphics3D computer graphics3D computer graphics are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images...
- Development of SporeDevelopment of SporeSpore is a video game developed by Maxis and designed by Will Wright, released in September 2008. The game has drawn wide attention for its ability to simulate the development of a species on a galactic scope, using its innovation of user-guided evolution via the use of procedural generation for...
External links
- Video of a interactive skeletal and model editor with introduction to the basic theory, University of Washington, USA.
- Deformable Objects and Characters project, University of Washington, USA. Has example videos of the techniques.
- Motion Libraries for Character Animation project, University of Washington, USA. Has example videos of the techniques.