Avatars

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Avatars

• MAJ Thomas E. Miller
• Naval Postgraduate School
• millert_at_cs.nps.navy.mil

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Avatars

• In virtual reality, an avatar is a
  symbolic-virtual-world representation of a
  real-world person. Using an avatar, the
  real-world person moves through the virtual
  world, seeing what the avatar sees, and
  interacting by telling the avatar what to do.

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Overview

• Motivation
• Avatar Features
• Geometric Body Modeling
• Behaviors
• Participants
• Conclusions
• References
• Questions

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Motivation

• Human Factors Analysis
• Crash simulation, Motion analysis, Workplace
  assessment
• Entertainment
• Dance or movement notation, animation, games
• Communication
• Virtual conferencing
• Education and Training
• Motion understanding, Battlefield Simulation

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Avatar Features

• Features of an avatar can be divided into two
  groups
• Physical description of the avatar
• Behaviors of the avatar ( how it moves, interacts
  with its environment etc )
• 
  

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Example
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Geometric Body Modeling

• There are two basic schemes to model bodies
• Boundary Schemes models surfaces
• Collection of 3D points, Lines or Parallel Rings
  Polygons Curved Surfaces ( Patches )
• Volumetric Schemes
• Voxels, Constructive Solid Geometry, Potential
  Functions

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Boundary Schemes

• Collection of 3D points, Lines or Strips
• Used in vector graphic displays
• Polygons ( Polyhedral )
• Relatively simple to define, manipulate and
  display
• Polygons best define flat shapes, therefore
  models get complex
• Most common form of modeling

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JackMOO
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Boundary Schemes continued

• Curved Surfaces
• Use curved surfaces defined by parametric
  equations called patches
• Display constraints make these models bad for
  real-time use but good for animation
• Care must be taken in modeling the joint
  connections
• Tin Toy ( 1988, Pixar ) 1st Computer animated
  film to win an Oscar!
  

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Tin Toy
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Volumetric Schemes

• Voxels
• Tessellation of cubes or parallelepipeds
• Very accurate representation ( anatomical )
• High resolution image is expensive in space
• Real time display is difficult
• 
  

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Volumetric Schemes continued

• Constructive Solid Geometry
• Dont need to regularly tessalate
• Not restricted to cubes
• Must polygonize primitives for display
• More useful if the set of primitives is
  restricted in one or more ways
• 
  

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Volumetric Schemes continued

• Single Primitive Systems
• Ellipsoids cartoony looking
• Cylinders used for early models joint
  connections bad, bad cross sections
• Superquadrics ( mathematical generalization of
  spheres ) used overlapping for faces and
  figures
• Spheres regular 3D objects or as flat shaded
  disks to form scales ( high density of overlap )

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Volumetric Schemes continued

• Potential Functions
• Volume of a sphere treated as a potential
  function with a center and a field function that
  decreases monotonically from the center outward
• No set radius, surface is determined by threshold
  values
• Adjacent potential functions have overlapping
  fields, therefore a point in space is defined by
  their sums and they blend smoothly
• Difficulty in generating many overlapping
  functions
• Very slow display times

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Behaviors

• Avatar Motion
• Autonomy
• Attention Control motor behaviors triggered by
  action requests
• Locomotion with Anticipation avatar positions
  itself appropriately to interact with a target
  object

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Defining Avatar Motion

• Motion capture from direct live video or sensors
• Pre-stored motion data
• 2D sprites
• 3D global transformations
• 3D local (joint) transformations

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Defining Avatar Motioncontinued

• Motion synthesis
• Joint angle interpolation
• Inverse kinematics ( Determining joint angles
  from postures )
• Dynamics
• Other generators (e.g. locomotion, faces)

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Motion Synthesis Examples

• End effector position and orientation can control
  joints along an articulated chain
• A path or footsteps can control leg and foot
  rotations through a locomotion model
• A balance constraint can be superimposed on gross
  body motions

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Motion Synthesis Examplescontinued

• Dynamics calculations can move joints subject to
  arbitrary external and internal applied forces
• Secondary motions can enhance a simpler form

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Pre-stored Motion Data

• Advantages
• Speed of execution
• Algorithmic security
• minimizes computation

• Disadvantages
• Lack of generality
• every joint must be controlled explicitly
• Lack of anthropometric extensibility
• changing joint-to-joint distances will change the
  computed locations of end effectors, making
  external constraints and contacts impossible to
  maintain

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Motion Synthesis

• Advantages
• Reduced parameter set size
• less information needs to be acquired or
  communicated
• Generalized motion control
• walk, run, jump, etc.

• Disadvantages
• Difficulty of inventing natural-looking motions
• Possibility of no solution or poor computational
  result
• Invalid position results

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Whos Doing What ?

• Jack UPenn, Transom Corp/EAI
• DI-Guy Boston Dynamics Video
• Blaxxun Avatar Den, Avatar Studio,
• Cybertown

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Whos Doing What ?continued

• Chatteries - Active Worlds, Excite Chat
• Games - Everquest
• Web3D Consortium Human Animation Working Group
• HoloDesk/Skeleton Builder continuous mesh
  conversions of H-Anim humanoids

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Jack

• An interactive system for definition,
  manipulation, animation, and performance analysis
  of virtual human figures
• Can be substituted for live individuals for
  workspace or cockpit evaluation.
• Demonstrates various human limitations,
  constraints, and capabilities.

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Jackcontinued

• May be moved in real-time by position and
  orientation information or other motion
  generators such as walk-to or look-at.
• May have its actions synthesized by a program so
  that it can make its own decisions, navigate
  spaces, and so on.
• Represents anyone'' rather than a single
  specific person or character

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Transom/EAI

• In 1996, Transom acquired from the University of
  Pennsylvania the worldwide, exclusive rights to
  further develop, commercialize, and support the
  Jack software.
• Now in its third commercial release under the
  trade name Transom Jack, the original Jack
  software was the result of over 10 years and 14
  million of research and development at Penns
  Center for Human Modeling Simulation under the
  direction of Professor Norman I. Badler.

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Jack
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More Jack
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DI Guy

• DI-Guy is software for adding life-like human
  characters to real-time simulated environments.
• Each character moves realistically, responds to
  simple commands, and travels about the
  environment as directed.
• DI-Guy animates each character automatically
• Even when switching from one activity to another,
  DI-Guy makes seamless transitions and moves
  naturally like a real person.

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DI Guycontinued

• DI-Guy is Real Time
• Fully interactive
• DI-Guy Works in DIS/HLA
• Used for high-end simulation and virtual reality
  application by customers like Lockheed Martin,
  Booz Allen Hamilton, Raytheon, STRICOM, CBDCOM,
  ARDEC, Naval Air Warfare Center, Mitsubishi Heavy
  Industries, and the US Army, Navy, and Marines.

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DI Guy Actions

• Stand
• Walk, Walk backwards Walk crouched
• Go prone
• Kneel
• Crawl
• Fire Weapon
• Die

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Boston Dynamics

• Boston Dynamics was formed in 1992 as a spin-off
  from the MIT Artificial Intelligence Laboratory,
  where the founders developed advanced robotic
  systems.
• The robotics work done at MIT was adapted at
  Boston Dynamics to apply it to lifelike human
  animation and analysis.

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The DI Guy
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Show BDI Video
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Blaxxun Avatar Den
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Blaxxun Avatar Studio( Set Body Type/Dimensions )
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Blaxxun Avatar Studio( Select Clothing )
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Blaxxun Avatar Studio( Add Animations )
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Blaxxun Avatar Studio( Scan In Your Face )
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Active Worlds
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Excite Chat
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Humanoid Animation Standard 1.1

• Goal is create a scheme for interoperable virtual
  humans
• Model once, animate anywhere
• Guiding Principles
• Compatibility
• Flexibility
• Simplicity

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H-ANIM

• Humanoid is a hierarchical collection of
  segments, each of which is attached to a joint
• Each segment is a separate piece of geometry
• Joints allow segments to be rotated relative to
  one another

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Essential Elements of H-Anim

• Naming Convention
• Defines a set of names for each joint and segment
  in the human body
• Neutral Body Pose ( default starting position )
• All joint rotations are zero

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JointHierarchy
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Nancy
Nancy, Running Woman, Stricom Demo
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Evaluating Avatars

• What do you want to model with your avatar?
• What does the avatar need to look like?
• What characteristics of the avatar are important
  to success of the application?

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Some Evaluation Criteria

• Appearance
• Cartoon Shape to Physiologically Accurate Model
• Function
• Cartoon Actions to Human Limitations
• Time
• Off-Line Generation to Real-Time Production

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Some Evaluation Criteriacontinued

• Autonomy
• Direct animation to Intelligent/Cognitive
• Individuality
• Specific Person to Varying Personalities
• Level and Control of Detail
• Appropriate level of detail for model

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Conclusions

• Build avatars to meet your modeling needs.
• Never build your own avatar. Use a tool or buy it
  from someone.
• Adds visually compelling content to your
  simulation.
• ActiveWorlds ticker symbol is AWLD.

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References

• 1. Ames, Nadeau, D. and Moreland. VRML 2.0
  Sourcebook , ed. 2. John Wiley Sons, Inc, NY,
  1997.
• 2. Badler, Phillips, Webber. Simulating Humans.
  Oxford University Press, NY, 1993.
• 3. Pixar
• http//www.pixar.com/funstuff/sh_videodescrip.html

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References continued

• JackMoo A web-based system for virtual human
  simulation
• http//www.cis.upenn.edu/jshi/JackMOO/webs.htm
• 5. The Humanoid Animation Working Group
• http//ece.uwaterloo.ca/h-anim/

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References continued

• Roehl and Fletcher. The H-Anim Standard (Tutorial
  Notes), web3D/ VRML2000, Feb 21 24, 2000.
• Cindy Ballreich
• http//www.ballreich.net/vrml/h-anim/

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References continued

• Transom Corporation
• http//www.transom.com/Public/index.html
• 9. Dr. Norman Badler
• http//www.cis.upenn.edu/badler/paperlist.html
• 10. Boston Dynamics
• http//www.bdi.com

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Questions ?