W60: 3D Modeling and Animation

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W60 3D Modeling and Animation
Modeling and Animation Concepts
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Overview

• Modeling
• Animation
• Many figures and examples in this set of lectures
  are from The Art of 3D Computer Animation and
  Imaging, by I. Kerlow

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Skin and Bones

• Skeleton with joined bones
• Can add skin on top of bones
• Automatic or hand-tunedskinning

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Particles
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Algorithmic Primitives
Algorithms for trees, mountains, grass, fur,
lightning, fire,
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Hierarchical models

• When animation is desired, objects may have parts
  that move with respect to each other
• Object represented as hierarchy
• Often there are joints with motion constraints
• E.g. represent wheels of car as sub-objects with
  rotational motion (car moves 2 pi r per rotation)

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DAG models

• Could use tree torepresent object
• Actually, a DAG (directed acyclicgraph) is
  better can re-use objects
• Note that each arrow needs aseparate modeling
  transform
• In object-oriented graphics, alsoneed motion
  constraints with eacharrow

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Example Robot

• Traverse DAG using DFS (or BFS)
• Push and pop matrices along the way (e.g.
  left-child right-sibling) (joint position
  parameters?)

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Animation

• Suppose you want the robot to pick up a can of
  oil to drink. How?
• You could set the joint positions at each
  moment in the animation (kinematics)

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Inverse Kinematics

• You cant just invert the joint transformations
• Joint settings arent even necessarily unique
  for a hand position!
• Inverse kinematics figure out from the hand
  position where the joints should be set.

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Using Inverse Kinematics

• Specify joint constraintsand priorities
• Move end effector(or object pose)
• Let the system figureout joint positions

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Motion Capture

• More realistic motion sequences can be
  generated by Motion Capture
• Attach joint position indicatorsto real actors
• Record live action

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Morphing

• Image/video morphing smoothly shifting from one
  image to another
• First popularized in a Michael Jackson video
• Method for video a combination of
• Identifying corresponding points in images over
  time
• Warping both images, gradually moving control
  points from location in first image to location
  in the second
• Cross-fading from first image sequence to second

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3D Morphing

• Define 3D before andafter shapes as e.g. NURBS
  surfaces with same number ofcontrol points
• Gradually move control points fromfirst setting
  to second
• Specify key poses e.g. smile, frown, 12 frames
  of walking motion

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Combined approaches
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Character Animation

• To make computer graphics(or cartoon drawings)
  come alive

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Personality through Pose, Expression, Motion,
Timing
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