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Animation Low-Level behaviors Overview Keyframing Motion Capture Simulation Low-Level Behaviors Keyframing Motion Capture Simulation Generating Motion What matters? Quality of motion appropriate for rendering style and frame rate Controllable from UI Controllable from AI

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Animation l.jpg

Animation

Low-Level behaviors Overview

Keyframing

Motion Capture

Simulation

IAT 410


Low level behaviors l.jpg
Low-Level Behaviors

  • Keyframing

  • Motion Capture

  • Simulation

IAT 410


Generating motion l.jpg
Generating Motion

  • What matters?

    • Quality of motion appropriate for rendering style and frame rate

    • Controllable from UI

    • Controllable from AI

    • Personality of the animated character

IAT 410



Keyframing l.jpg
Keyframing

  • Fine level of control

  • Quality of motion depends on skill of animator

IAT 410


Motion capture l.jpg
Motion Capture

  • Natural-looking motion

  • Hard to generalize motions

    • Registration is difficult

    • “Weightless” according to professional animators

IAT 410


Motion capture images courtesy microsoft motion capture group l.jpg
Motion CaptureImages courtesy Microsoft Motion Capture Group

IAT 410


Simulation broadly defined l.jpg
Simulation (Broadly Defined)

  • Physics is hard to simulate

  • Pseudo-physics is somewhat hard

  • Control is very hard

  • Gives Generalization + Interactivity

Desired

Behavior

Forces and Torques

Model

Numerical Integrator

User/AI

Control

State

Graphics

IAT 410


When to use what method l.jpg
When to Use What Method?

  • Keyframing

    • Sprites and other simple animations

    • Non-human characters

    • Coarse collision detection

  • Motion Capture

    • Human figures

    • Subtle motions, long motions

  • Simulation

    • Passive simulations

    • When interactivity w/ motion is important

IAT 410


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Keyframing

IAT 410


Keyframing11 l.jpg
Keyframing

IAT 410



Keyframing13 l.jpg
Keyframing

  • Fine level of control

  • Quality of motion depends on skill of animator

IAT 410


Hand drawn animation 2d l.jpg
Hand Drawn Animation -- 2D

  • Sketches

  • Pencil tests

  • Inking

  • Coloring

  • Digitize to sprites

IAT 410


Computer animation 2d or 3d l.jpg
Computer Animation: 2D or 3D

  • Sketches

  • Models and materials

  • Key configurations

  • Playback of motion or render to sprites

IAT 410


Keyframing16 l.jpg

The development process:

Adjust trajectory

Playback motion

Parameters:

Locations

Joint angles

Shape -- flexible objects

Material properties

Camera Motion

Lighting

Keyframing

IAT 410


Keyframing interpolation l.jpg
Keyframing Interpolation

  • Inbetweening

v

1,2,3 4 5 6 7,8,9…

Linear

time

v

1,2,3 4 5 6 7,8,9…

Slow in, Slow out

time

IAT 410



Key frames l.jpg
Key Frames

1

2

3

IAT 410


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Key Frames

  • Timeline

  • 1 2 3 3 1

IAT 410


Inbetweening l.jpg
Inbetweening

  • Frame dependent (“wrong”) slow-in/out

    • Iterate once per frame

    • This is a variant on the Infinite Impulse Response (IIR) filter:

IAT 410


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Inbetweening

  • Frame-Independent (“right”) slow in/out

    • Compute acceleration a

Time of last frame

Time

Tend

IAT 410


Spline driven animation l.jpg
Spline-driven Animation

y

x,y = Q(u)

for u:[0,1]

  • Equal arc lengths

  • Equal spacing in u

x

IAT 410


Reparameterize arc length l.jpg
Reparameterize Arc Length

  • S= A(u) = arc length

  • Reparam:

  • Find:

    Bisection search for a value

    of u where A(u) = S with a

    numerical evaluation of A(u)

    (Details in Watt & Watt)

IAT 410


Keyframing constraints l.jpg
Keyframing -- Constraints

  • Joint limits

  • Position limits

  • Inverse kinematics

IAT 410




Kinematics l.jpg
Kinematics

  • The study of motion without regard to the forces that cause it

Draw graphics

Specify fewer Degrees Of

Freedom (DOF)

More intuitive control of DOF

Pull on hand

Glue feet to ground

IAT 410




What makes ik hard l.jpg
What makes IK Hard?

  • Many DOF -- non-linear transcendental equations

  • Redundancies

    • Choose a solution that is “closest” to the current configuration

    • Move outermost links the most

    • Energy minimization

    • Minimum time

IAT 410


Ik difficulties l.jpg
IK Difficulties

  • Singularities

    • Equations are ill-conditioned near singularities

    • High state-space velocities for low Cartesian velocities

  • Goal of “Natural Looking” motion

    • Minimize jerk (3rd derivative)

IAT 410


Motion capture33 l.jpg
Motion Capture

  • What do we need to know?

    • X, Y, Z

    • Roll, Pitch, Yaw

  • Errors cause

    • Joints to come apart

    • Links grow/shrink

    • Bad contact points

  • Sampling Rate and Accuracy

IAT 410


Motion capture34 l.jpg
Motion Capture

  • Goals:

    • Realistic motion

    • Lots of different motions (300-1000)

    • Contact

  • Appropriate game genres

    • Sports

    • Fighting

    • Human characters

IAT 410


Applications l.jpg
Applications

Movies, TV

Video games

Performance animation

IAT 410




Plan out shoots carefully l.jpg
Plan out Shoots Carefully

  • Know needed actions (80-100 takes/day)

    • Bridges between actions

    • Speed of actions

    • Starting/ending positions

  • Hire the right actor

    • Watch for idiosyncrasies in motion

    • Good match in proportions

IAT 410


Sensor placement l.jpg
Sensor Placement

  • Place markers carefully

    • Capture enough information

    • Watch for marker movement

  • Check data part way through shoot

  • Videotape everything!

IAT 410



Technology l.jpg
Technology

  • Numerous technologies

  • Record energy transfer

    • Light

    • Electromagnetism

    • Mechanical skeletons

IAT 410


Technology42 l.jpg
Technology

  • Passive reflection – Peak Performance Tech

    • Hand or semi-automatically digitized

    • Video

    • Time consuming

  • Issues

    • No glossy or reflective materials

    • Tight clothing

    • Marker occlusion by props

    • High frames/sec

IAT 410


Technology43 l.jpg
Technology

  • Passive reflection --Acclaim, Motion Analysis

    • Automatically digitized

    • 240Hz

    • Not real-time, Correspondence

    • 3+ markers/body part

    • 2+ cameras for 3D position data

IAT 410


Technology44 l.jpg
Technology

  • Vicon Motion Systems

    • Retroreflective paint on reflectors

    • Lights on camera

    • Very high contrast markers

IAT 410


Technology45 l.jpg
Technology

  • Active light sources -- Optotrak

    • Automatically digitized

    • 256 markers

    • 3500 marker/sec

    • Real-time

    • Specialized cameras

IAT 410


Technology46 l.jpg
Technology

  • Electromagnetic Transducers

    • Ascension Flock of Birds, etc

    • Polhemus Fastrak, etc

  • Limited range/resolution

    • Tethered (cables to box)

    • Metal in environment (treadmill, Rebar!)

    • No identification problem

    • 6DOF Realtime

    • 30-144 Hz 13-18 markers

IAT 410


Technology47 l.jpg
Technology

  • Exoskeleton + angle sensors

    • Analogous

    • Tethered

    • No identification problem

    • Realtime - 500Hz

    • No range limit - Fit

    • Rigid body approximation

IAT 410


Technology48 l.jpg

Dataglove

Low accuracy

Focused resolution

Monkey

High accuracy

High data rate

Not realistic motion

No paid actor

Technology

Mechanical motion capture

IAT 410


Technology49 l.jpg
Technology

  • Technology issues

    • Resolution/range of motion

    • Calibration

    • Accuracy

    • Occlusion/Correspondence

IAT 410


Animation issues l.jpg
Animation Issues

  • Style

  • Scaling

  • Generalization

IAT 410


Resolution l.jpg
Resolution

  • Positioning of camera

IAT 410


Markers calibration l.jpg
Markers, Calibration

  • Marker Placement

    • Location should move rigidly with joint

    • Stay away from bulging muscles, loose skin

    • Shoulders: Skeletal motion not closely tied to skin motion

  • Calibration

    • Zero position

    • Fine calibration by hand

IAT 410


Calibration l.jpg
Calibration

  • Finding Joint Locations

    • Move markers to joint centers

      • Assume rigid links, rotary joints

  • Shoulder?

IAT 410


Calibration54 l.jpg
Calibration

  • Extract best limb lengths

  • Use estimator to compute limb length

  • Minimize or reject outliers

IAT 410


Calibration55 l.jpg
Calibration

  • Example estimator:

    • 508 frames of walking

    • 6 bad frames

    • Collarbone to shoulder:

      • Hand editing: 13.3cm

      • Estimator: 13.2cm

      • Arithmetic mean: 14.1cm

IAT 410


Accuracy l.jpg
Accuracy

  • Marker movement

  • Noise in sensor readings

  • Skew in measurement time

  • Environment restrictions

  • Frame rate

    • High frame rate allows good filtering

IAT 410


Camera calibration l.jpg
Camera Calibration

  • Internal camera parameters

    • Optical distortion of lens

  • External parameters

    • Position and orientation

  • Correlation between multiple cameras

IAT 410


Model based techniques l.jpg
Model-Based Techniques

  • Restricted search space for markers

  • Dynamics (velocity integration)

    • No infinite accelerations

  • Model of behavior

  • Model of bodies of occlusion

    • Objects don’t pass through each other

IAT 410


Scaling animation l.jpg
Scaling Animation

  • Contact

  • Movement style

  • Inverse kinematics

IAT 410


Generalizating animation l.jpg
Generalizating Animation

  • Interpolation Synthesis for Articulated Figure Motion

  • Wiley and Hahn

  • IEEE CG&A v17#6

IAT 410


Generalizating animation61 l.jpg
Generalizating Animation

  • Keyframes as constraints in a smooth deformation

    • Create functions by hand that warp the joint angle curves through time

  • Keyframe placing the ball on the racket at impact

    Motion Warping

    Witkin and Popovic, SIGGRAPH’95

IAT 410


Motion warping l.jpg
Motion Warping

  • For each joint angle curve C(t)

  • Cnew(t) = C(t) * A(t) + B(t)

  • A(t) is usually a smooth, gentle curve

IAT 410


Generalizating animation63 l.jpg
Generalizating Animation

  • Motion Editing With Spacetime Constraints

    • Michael Gleicher

    • 1997 Symposium on Interactive 3D Graphics

IAT 410


Blending animations l.jpg
Blending Animations

  • Efficient Generation of Motion Transitions Using Spacetime Constraints

    • Rose, Guenter, Bodenheimer, Cohen

    • Siggraph ’96

    • Uses dynamics to compute plausible paths

    • Blends these paths

IAT 410


Simulation l.jpg
Simulation

  • Modeling the real world with simple physics

    • Realism

    • A set of rules

    • Better interactivity

  • Objects or Characters

IAT 410


Passive no muscles or motors l.jpg
Passive -- No muscles or motors

Active -- Internal source of energy

IAT 410


Equations of motion l.jpg
Equations of Motion

  • Water

  • Explosions

  • Rigid body models

IAT 410


Control systems l.jpg
Control Systems

  • Wide variety of behaviors

  • Transitions between behaviors

  • Controllable by AI or UI

  • Robust

IAT 410



Generating motion70 l.jpg
Generating Motion

  • What matters?

    • Quality of motion appropriate for rendering style and frame rate

    • Controllable from UI

    • Controllable from AI

    • Skills of the animated character

    • Personality of the animated character

IAT 410


Keyframing71 l.jpg
Keyframing

  • Fine level of control

  • Quality of motion depends on skill of animator

IAT 410


Motion capture72 l.jpg
Motion Capture

  • Natural-looking motion

  • Hard to generalize motions

    • Registration is difficult

  • Often seems “weightless” – Bill Kroyer, Rhythm & Hues

IAT 410


Simulation broadly defined73 l.jpg
Simulation (Broadly Defined)

  • Physics is hard to simulate

  • Pseudo-physics is somewhat hard

  • Control is very hard

  • Gives Generalization + Interactivity

Desired

Behavior

Forces and Torques

Model

Numerical Integrator

User/AI

Control

State

Graphics

IAT 410


When to use what method74 l.jpg
When to Use What Method?

  • Keyframing

    • Sprites and other simple animations

    • Non-human characters

    • Coarse collision detection

  • Motion Capture

    • Human figures

    • Subtle motions, long motions

  • Simulation

    • Passive simulations

    • When interactivity w/ motion is important

IAT 410


Integration of technologies l.jpg
Integration of Technologies

  • Layering

    • Add hand/finger motion later

    • Facial animation

  • Use keyframing to modify data

    • Fix holes in data

  • Use motion capture to drive simulation

IAT 410


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