Quiz 3, Go to www.cs.northwestern.edu/~animation/Project3/project.php

Please list the author and basic scene description.Write notes for our in-class critique based upon the following criteria

(positive and negative comments) • Created a Scene (backdrop & ground-plane): • Hero lighting

– Is it obvious where the viewer should be looking: – Interesting composition & sense of relationship: – Shadows

• Mood lighting:– Same objects, same composition, same camera angle as hero lighting: – Different light focusing on different character: – Conveys mood: – Main character still visible: – Main character still belongs to scene: – Shadows

Business

• Thanks carefully naming your Project 3 files – (Your TA appreciates it :)

• Final project proposal round 2 due Thursday– Start a web page (HTML format)– Who's in your group

– Overview with Goals

– Time table (schedule for what will be done when)• Include model sheets, story boards, material examples, etc

Character Modeling: Key Frame Animation

Amy Gooch

CS395: Intro to Animation

Summer 2004

3D Animation

Rendering• 3D Scene and Motion• Sequence of Frames

– Rates: Video 30fps, Film 24fps

• Persistence of Vision

Animator must create ..• Illusion of Life• Weight

Animation

• Almost every property of every object in the scene can be animated (changed through time) – Models, cameras, …

– Transformations: ‘• Move

• Rotate

• Scale

– Modifications/Deformation: edits, bends, twists, manipulating a skeleton

– materials, colors, textures

Animation

• 3D Scene does not have – Gravity – Weight– Force – interactions between objects– (bit of a lie)

• You must make it seem so!

Preproduction Phases

• Screen-play

• Storyboards

• Character development

3D Characters

• Digital actor– Tin can– Sack of flower– Butterfly, beetle – Bird– Flower– Robot– Humanoid– Etc…

Typical Character

• Mechanics of movement must be convincing

• Skin and clothing moves & bends appropriately

• This process of preparing character controls is called rigging– Fully rigged character has

• Skeleton joints, surfaces, deformers, expressions, Set Driven Key, constraints, IK, Blendshapes, etc

Typical Character

Character Resolution

• Use low resolution character that has surfaces “parented” to skeleton– Allows interactive animations– Switch to full resolution character later

• Rag Doll; Skeleton by Proxy tutorial

http://www.goldenxp.com/tutorials/ragdoll/ragdoll1.htm

Typical Character Animation Workflow

• Character Design

• Model

• Skeleton Rigging

• Binding

• Animation

• Integration

• Rendering

For Project 4

• Concentrate on – Character Design

• Model Sheet with poses

– Modeling (simple)– Skeleton Rigging– Binding

12Principles.ppt

Thursday

• Quiz

• Character Model Sheets due

• Read Project 4 Web page carefully

Character Modeling: Key Frame Animation

Amy Gooch

CS395: Intro to Animation

Summer 2004

Primary methods of Animation

• Keyframe

• Procedural– Expressions– Scripting

• Dynamics/Simulation– Physics

• Motion Capture

• Combinations of the above

Keyframe Workflow

1. Set Keys– Usually extreme positions– Less is more: Keys only the properties being

animated

2. Set Interpolation– Specify how to get from one key to another. – Secondary, but a necessary step.

3. Scrub Time slider and refine motion curve

Setting Keys

• Start with extreme positions

• Add intermediate positions– Secondary motion

• Less is more– Don’t add keys for properties that you are not

animating– Easier to manage/edit fewer keys

Motion Curves: Position vs. Time

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Motion Curves

When is the box going

• Forward?• Backward?• Fastest?

Is the box • Starting from stop

or at rest?• Stopping at the end

or continuing?

Interpolation

• Specify how to get from one key to the other (inbetweening)

• Common types– Step: stay at the same value, then suddenly

switch– Linear: change at constant rate– Spline/Smooth: make it smooth

• All of these (and more) are useful and appropriate in the right circumstance

Smooth Interpolation

Soft changes of direction

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Linear Interpolation

Hard changes of direction

Appears to be contacting other objects, instant changes

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Step Interpolation

Object reappears in a totally different position

This is very useful. When?

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Ease In/Out

Heavy objects take a while to get going

• trains

Use interpolation to emphasize this.

Ease in/out –or- Slow in/out means to leave the key slowly

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Timing of the action

• Ahead of the story– Something will happened before we know what it is

• audience not yet aware

• character may knows what’s up

– Ex Alien Song

• Behind the story– Audience knows before character knows

– Ex: KnickKnack (1989)

• Keep audience Interested!

Motion of characters

• Along with key frame animation we can use kinematics– Kinematics = study of motion without regard to

the forces that cause it

Specify fewer degrees of freedom

More intuitive control

User Control of Kinematic Characters

• Joint Space– Position all joints (fine level of control)

• Cartesian Space– Specify environmental interactions easily

• Most DOF computed automatically

Inverse Kinematics

• Balance = keep center-of-mass over support polygon

• Control– Ex: position vaulter’s hands on line between

shoulder and vault– Ex: Compute knee angles that will give runner

the right leg length

What makes IK hard

• Redundancy

What makes IK hard

• Singularities

What make IK hard

• Goal of “natural looking” motion– Minimum jerk– Equilibrium point trajectories

Resources

• Laws of Cartoon Physics– http://www.cc.gatech.edu

/classes/cs8113f_97_spring/cartoon.html

• Learning Maya Tutorial list– http://www.learning-maya.com/rigging.php – Skeleton Tutorial

• http://web.alfredstate.edu/ciat/tutorials/SkeletonSetup.htm

– Rag Doll; Skeleton by Proxy tutorial• http://www.goldenxp.com/tutorials/ragdoll/ragdoll1.htm

– 5-minute Leg Rig• http://www.noir.org/tutorials/Xen%20Wildman/legrig/legrigtut.html

Credits

• Winny

• Jessica Hodgins

• http://www.cs.dartmouth.edu/~brd/Teaching/Animation/animation.html