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7M836 Animation & Rendering. Animation. Jakob Beetz J.Beetz@tue.nl. Joran Jessurun A.J.Jessurun@tue.nl. Week 8. Subject: Virtual Reality and Examples When: June 14 th Where: Design Systems Lab. (Vertigo 9.16). Animation. History of cartoon and computer animation

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7m836 animation rendering

7M836 Animation & Rendering


Jakob Beetz


Joran Jessurun


week 8
Week 8

Subject: Virtual Reality and Examples

When: June 14th

Where: Design Systems Lab. (Vertigo 9.16)

  • History of cartoon and computer animation
  • Extensive description of techniques and algorithms

Rick ParentComputer Animation, Algorithms and Techniqueswww.cis.ohio-state.edu/~parent/book/outline.html

  • How to make an animation
  • Exampleswww.pixar.com
  • Animation
    • “To give live to”
    • Make objects change over timeaccording to scripted actions
    • By showing a sequence of fastchanging images
  • Series images (frames)
    • Film 24 fps
    • Video 30 fps => 1 hour animation 108000 frames
what can be animated
What can be animated?
  • Position and orientation of objects
  • Geometry (shape) and scaling of objects
  • Illumination
  • Reflection
  • Camera
  • In fact, everything!
animation process traditional
Animation process - traditional
  • Storyboard
    • The story
    • Sequence of images with descriptions
  • Key frames
    • Draw a number of important images (key frames)
    • Motion-based description
  • Inbetweens
    • Draw the rest of the frames
  • Painting
    • Redraw frames onto cels
    • Color them in
  • Put animation onto film
computer animation

Key framing

Computer animation
  • Computer animation pipeline
    • 3D modeling
    • Motion specification
    • Motion simulation
    • Rendering
    • Post-processing
keyframe animation
Keyframe animation
  • Each “keyframe” specified by a number of key-parameters (state)
  • Inbetweening: Interpolate these parameters
keyframe animation1
Keyframe animation
  • For each key parameter, specify value at “important” frames
  • Computer creates path for each parameter by interpolating this key parameter for inbetween frames
  • Linear interpolation
    • Usually discontinuities
    • Not a smooth movement
  • Spline interpolation
    • Smooth transitions
    • Beware of unwanted side effects
interpolation speed control
Interpolation – speed control
  • Include velocity of interpolation
    • It is often more realistic to start a movement slowly, then speed up, and end it again slowly
    • Use speed curve
      • Speed curve relates time with position on interpolation spline
      • Position on interpolation spline determines interpolated key parameter value
keyframing summarized
Keyframing summarized
  • Specification of key frames/parameters
    • Determine key parameters and their values at certain important points in time
    • Specify type of interpolation
  • Specify speed curve for interpolation
  • Computer generates inbetween frames
animation of articulated structures
Animation of articulated structures
  • Articulated structure:
    • Object consists of a number of (sub-)objects (links) connected by joints
    • Each joint is specified by at least one (key-)parameter
    • Movement of object described by changing parameter values
articulated structure
Skeleton consists of 14 joints

Each joint has 2 or 3 degrees of freedom

Some parameters constrained

Articulated structure
  • Kinematics is the study of movement of (hierarchical) objects
    • Position, orientation, velocity, acceleration
    • Without taking into account dynamic properties (forces) (dynamics)
  • Forward kinematics
  • Inverse kinematics
forward kinematics
Forward kinematics
  • Animator sets parameter values for joints
  • Computer computes positions/orientations for links links:
forward kinematics1
Forward kinematics
  • Animation by specification / interpolation of joint parameters
  • What to do when animation knows the desired end-position of the (sub-)object?
    • E.g. to grab something?
inverse kinematics
Inverse kinematics
  • Animator specifies position (and orientation) within scene at wich link (end-effector) has to be positioned
  • Computer computes joint parameter values to get link at desired position:
  • After that. computer computes positions of all links by applying these joint parameter values for all joints
inverse kinematics2
Inverse kinematics
  • Animation by specification / interpolation of end-effector position
  • Or animation by interpolation of joint parameter values at start and end frame
inverse kinematics3
Inverse kinematics
  • Problems
    • Often more than one solution
      • Extra requirements to solution
    • Result not always desired path (e.g. collisions)
    • What to do when end-effector position specified outside operation area of object?
inverse kinematics4
Inverse kinematics
  • Inverse kinematics is also used to compute dependency of joint parameter values
    • E.g. for object with closed loops
kinematics summarized
Kinematics summarized
  • Forward kinematics
    • Animator controls through joint parameters
    • Direct control over object state
    • Often many parameters to control
  • Inverse kinematics
    • Animator controls through position/orientation end-effector
    • Simpler specification of movements
      • Less parameters
      • Better feeling for positions in scene
    • Complex computations