Week 3/4 - Principles of Animation

Question 1

What are the stages of animation (in order)

Answer 1

Modelling
Rigging
Skinning
Animation

Question 2

What fps is appropriate for film?

Answer 2

24 fps

Question 3

What fps is appropriate for VR?

Answer 3

90 fps

Question 4

What is squash in animation?

Answer 4

Flattening an object or character by pressure or it’s own power

Question 5

What is stretch in animation?

Answer 5

Increase the sense of speed and emphasis it’s squash by contrast

Question 6

What timing in animation is used for heavy and light objects? Which ones move faster/slower?

Answer 6

Heavy objects move slower, lighter ones faster.

Note: timing completely changes the interpolation of the motion

Question 7

What are the two ways we describe and generate motion in a scene?

Answer 7

production - always offline rendered like movies, fancier because we get more time to generate them

interactive - games, simulators, VR

This is why less realism in games/simulators vs movies

Question 8

What is tweening?

Answer 8

Generating frames in between keyframes of real movement

Is boring so is normally automatically generated

Question 9

What is rigging?

Answer 9

Building animation controls for 3D models (maybe construct bones for a user animation)

Question 10

What information does the articulated skeleton carry?

Answer 10

Topology, what is connected to what

Geometric relations of joins

Tree structure of the body parts, which should be in absence of loops

Question 11

What does forward kinematics predict?

Answer 11

Describes the position of the body part (end effector) as a function of the joined angles

Animator provides the angles
Computer determines the position of the end effector

Question 12

What is the first phase for rigging?

Answer 12

Forward kinematics

Question 13

What do inverse kinematics predict?

Answer 13

Given the end effector position, returns the joint angles

Question 14

What makes inverse kinematics hard? What is it good for?

Answer 14

There could be multiple correct answers

There are constraints on the joints to be considered (might not be able to bend an elbow more than 180 degrees) this may cause no correct answer to exist

Can be time consuming for artists to design them

Animation may be inconsistent with physics

Pros:
Direct control is convenient

Implementation is straightforward

Question 15

Motion Capture

Answer 15

Recording a real world performance and extracts poses as a function of time from the raw data

Usually uses optical markers and high speed cameras

Good:
captures style, very subtle. nuance and very perfect realism

Cons:
Needs the ability to record someone

Question 16

What is retargeting for motion capture?

Answer 16

Translating marker positions into character controls (bone transformations)

Question 17

Most popular technique for skinning?

Answer 17

SSD (Skeleton subspace deformation)

Question 18

Techniques for skinning

Answer 18

Skeleton subspace deformation (SSD)

Out of scope:
- vertex blending
- matrix palette
- linear blend skinning

Question 19

Describe sub space deformation (SSD)

Answer 19

Attaching each vertex of the skin to single/multiple bones using weightings

The weights over all bones should be 1 for every vertex, and each weight should be non-negative

A vertex with multiple weights has all transformations applied to it and then the weighted average of those transformations is computed

This is not perfect though, it gets more complicated with the inner part of the arm. (not important for the courses high level view to go deeper than this)