IMD4003: Exam Review Notes

For IMD 4003: Computer Animation, taught by Chris Joslin

Lecture 13 – Character Animation V

• Walking and Locomotion: no drawing but certain elements are important (key positions)
• Walking is the main (skipping and jumping are less significant)
• Feet and Legs: shoulders opposing, motion of the legs are important
• Hips, Spine and Shoulders: maintaining centre of gravity; opposing rotation, swinging of arms and head
• Concept of Walking Forward
• Not the concept of timing the walk (maybe giving a range? But doubtful)
• Possible Question: How do different moods will affect posture style, stride length, personality, hips?
• Stride and Gait will definitely be on it
• Lower Body positions maybe but doubtful
• Transitions are less important
• Going up and down slopes will likely be a question
• Details are less important in this lecture

Lecture 14 – Match Moving 1

• Nothing about software
• Process is important (the diagram in the slides)
• Make sure you know a broad overview of each step, not the intricate details
• Pipeline is a good question (very important not to mix this with the process)
• Perspective Matching:
  • Focal Length, Height of Camera, Distance from Cam and Scale of Object, Film Back
  • Understand the process
  • Steps for adding rough geometry

Lecture 15 – Match Moving 2

• Software process is an interesting thing
• Photogrammetry is not as important but you should know
  • 3D, 2D projection: number of points you need to fix the rotation of the axis
  • Calculate degrees of freedom
  • Points of Intersect
  • Understand Parallax
• 2D Tracking:
  • Anatomy
  • Key-framing
  • Minimum Number of Tracks and Stair-stepping
• Plate Issues (MINOLS)

Lecture 16 – Match Moving 3

• Define Residuals
• 2 Types of Lens Distortion
• Masking
• Checkerboards may be a 2-mark question

Lecture 17 – Audio for Animation

• Definitions in red: types of sounds (diegetic, etc)
• Sound classifications
• Sound Effects: 3 categories and explain
• Examples are not replacements for answers
• Visual and Audio Processing: less important
• Time Perception: less important
• Sound for Character Development: pitch shifting ,etc is a good question
• Define Motifs and Lemotifs
• Plausibility vs. Reality: okay question
• Metaphoric Sound is an okay question – may ask for an example
• Sound Design Theory is less important
• Dialogue:
  • Walla will be on the exam
  • On-Screen Dialogue
  • Narration
  • Synthetic Languages maybe
  • Differences in Microphones
  • What’s a pop-shield
  • Sibilance and Plosives (maybe explain)

Lecture 18 – Particle Systems

• Many questions because it’s easy to ask them and its objective
• Example of fuzzy phenomena
• Generation (attributes; describe what is an emitter, particle, where it should be created, where the particle density is low; initial attributes like velocity, size, colour etc; understand, explain and regurgitate the equations), Dynamics (what forces may be applied, damping maybe, collisions maybe, other variables yes with an example) and Extinction (very good question – Age and Lifetime with 3 different ideas) are the most important
• Rendering is less important
• Metaballs is a 2-mark question
• Uses are less important

Lecture 19 – Motion Control 1

• Bad set of slides so this lecture and next lecture will most likely be combined
• Representation is important: describe the 3 types of representation
• No Motion Capture
• Time Manipulation yes (why we use them, what they are)
• Motion Curves is not likely
• Motion Retargeting might be on there (why we do it)
• Path Editing is doubtful

Lecture 20 – Motion Control 2

Interpolation

• Equation in terms of slow-in and slow-out are important (1 question combined – may give the equation and ask you to describe what they are) or he’ll most likely give you the 2 types of equations and ask you to give the interpolation
• Splines, etc

Quaternion

• Equations won’t be on it
• Concatenation equation will be a 4 mark question maybe
• Vector Rotations equation is important
• Why we do certain interpolations, why certain ones fail
• LERP and SLERP are 2 main things we should for sure remember

Lecture 22 – Dynamic Systems 1 (Cloth)

• Do not remember Cloth equations
• Understand spring damper, particle edge, how they’re connect, measured, assessed
• May give you an equation and ask you what’s going on
• Springs and Dampers: Computing Forces and Integrating Motions is a good question (steps)
• Spring and Damping Constants
• Forces equation is important – break it down
• Calculating Forces (with the e) is less important because it’s complicated
• Definitely break down aerodynamics question
• Calculate drag
• Give you fdrag equation and break it down
• Won’t give you n* equation
• Bending Forces
• Plastics Deformations is a good question
• Fracturing and Tearing is a good question
• System Stability: remember 2 of them (he won’ tell you which ones) understand what they are but you should understand time-step and why we choose more complex equations
• Other methods may be a 2-mark question at the end

Lecture 23 – Dynamic Systems 2 (Fluids)

Broken down into:

• Dynamic Systems
  • Fluid Dynamics – vector fields (rate of change by…), 2D Vector function
  • Diff between fluid and particle system
  • 10-mark question; Break down the Navier-Stokes equation (remember the equation)
  • Diffusion (…) term – have a clear idea of what it is and an example
  • Cell representation is important – so understand it
• Implementing Fluid Dynamics
• Problems with Fluid Simulation
  • 2-mark question

Lecture 24 – Dynamic Systems 3 (Hair)

Original lecture notes can be found at: Wen Tang (choose the Wen Tang.ppt slides).

IMD 4003: Match-Moving I

For IMD 4003: Computer Animation, taught by Chris Joslin

Contents

1. 1. Six Step Match-Moving Process
   1. Step 1. Evaluate Source Footage
   2. Step 2. Apply Additional Information
   3. Step 3. Define the Camera
   4. Step 4. Set Fitting and Layout
   5. Step 5. Testing the Match Move
   6. Step 6. Deliver the Scene
2. 2. Six Step Perspective Matching Process
   1. Step 1. Gather Data
   2. Step 2. Setting up the Camera
   3. Step 3. Add Rough Geometry
   4. Step 4. Create the Camera Rig
   5. Step 5. Evaluate and Adjust Camera
   6. Step 6. Finalize

1. Six Step Match-Moving Process

Match Moving: the process of taking a 2D image (single or sequence) and placing 3D objects, 3D lights and 3D cameras into it.

Step 1. Evaluate Source Footage

You need to know the following:

• Camera movement: how it's moving and its speed.
• Object visibility: what objects are in the scene, are the tracking markers there and when are they occluded.
• Format of the footage (ex. film or digital - graininess tends to be a problem).
• 3D Object: where it's going to go and how much accuracy you need.
• Final use: how will the footage be used and by whom.

Step 2. Apply Additional Information

You'll be using additional information to help you with the Match Move. This will come from the following:

• Camera Information: focal length, aperture, film time (length of shot).
• Survey Data: a detailed measurement of the set.
• Set Measurements: camera height, focus distance and real-lie scene object measurements.

Step 3. Define the Camera

You need to define the internal and external parameters of the camera using the software. There are 2 ways to do this:

1. Manual: this involves perspective matching and hand-tracking. This method is time-consuming because it's guesswork.
2. Automagic: software uses Photogrammetry (explained in the next lecture) to...
   1. Track the 2D features in the sequence;
   2. Analyze the movements of the 2D features using tracking markers (that you can set yourself); and finally
   3. Generate animated cameras and 3D tracking markers.
   This is the easiest method to use because it's automagic.

Step 4. Set Fitting and Layout

In this stage, you want to determine the spatial layout of the environment. You need to know:

• Amount of environment you need to reproduce which depends on what you're putting into the footage.

Step 5. Testing the Match Move

In this stage, you can composite a 3D Proxy Object (which is basically a crappy reference object) over the image sequence. Use a checkerboard texture to check for 3D "slippage".

Step 6. Deliver the Scene

You need to deliver your final scene to other people in the production pipeline. Some considerations you should take into account are the orientation and scale of the scene, objects that will need to be put into the scene, naming conventions, format, etc.

2. Six Step Perspective Matching Process

Perspective Matching: matching the perspective of a single image to a 3D scene you want to create.
This process is about exactly the same as the Match-Moving Process but with slight tweaks. Go through the tutorial, T07 - Match-Moving and it basically outlines everything here.

Step 1. Gather Data

There are 3 things you will likely need to guess: camera Focal Length, Set Measurements and Distance of Objects from camera. You can generally make a pretty good educated guess about all of them and the tweak the settings later in the process.

Step 2. Setting up the Camera

You do 3 things in this stage:

1. Evaluate the Scene: determine where the 3D object will go, the camera's position in the scene and position of the objects already in the scene.
2. Create a Camera with an Image Plane as the backdrop.
3. Estimate the Focal Length, Aperture and Height of Camera (yes, this is exactly like the last step).

Step 3. Add Rough Geometry

Place geometry with approximately correct dimensions into your scene. These objects represent real-life scene objects. Make sure they're approximately the right distance from the camera.

Step 4. Create the Camera Rig

Here is where we adjust the camera to view the scene better:

• Create a null Locator and snap it to a good rotational point in the scene;
• Make the Camera the child of the Locator;
• Use the Locator to rotate the camera into position;

Step 5. Evaluate and Adjust Camera

• Adjust the Focal Length: longer (bigger) lenses look flat whereas wide (smaller) lenses look distorted.
• Adjust the Scale and Position of the 3D Objects.

Step 6. Finalize

Use the objects in the scene to cast shadows and provide occlusion for your artificially placed 3D object.

Celebrate with a beer.

IMD 4003: Character Animation V

For IMD 4003: Computer Animation, taught by Chris Joslin

Contents

1. 1. The Mechanics of Walking
   1. 1.1 Four-Step Walk Cycle
   2. 1.2 Specific Body Movements
2. 2. Controlling Movement
   1. 2.1 Multiple Characters
   2. 2.2 Motion Transitions

1. The Mechanics of Walking

1.1 Four-Step Walk Cycle

There are 4 steps to this walk cycle that are repeated for each leg:

1. Extended Position: Feet are far apart and weight shifts to forward foot.
2. Recoil: Lowest point in the cycle; weight is distributed to the forward foot and the forward knee bends.
3. Passing: Forward knee straightens out and the back leg curls under the body.
4. High-Point: As the forward leg straightens, the body moves into its highest position. The weight is transferred to the ball of the forward foot and the passing foot 'catches' the fall.

The image below uses the term, “Contact” where we use the term, “Extended Position.rdquo; There is no difference.

The above image is from idelworm.com. Visit this site for a thorough explanation of how to create your own walk-cycle.

1.2 Specific Body Movements

The following outlines the different parts of your body that are affected when you're walking. One thing to note is that you should always start animating from the extreme poses (ie. start with the Extended Position and fill in the rest).

Feet and Legs

• The feet propel the body forward by pushing your body out of balance and then catch your weight. Always keep your joints slightly bend to look natural.
• Add Personality to the walk by changing the stride:
  • Stride Width: the stide width affects the perceived weight of the character; wide stances appear heavier, stronger and more masculine, whereas narrow stances appear feminine. Faster walks have longer strides (vice-versa for slower walks).
  • Stride Length: should appear equal otherwise your character will look like they have a limp.

Hips, Spine and Shoulders

• Your balance starts at your hips so therefore all of your motions (within reason) start at your hips (it's your centre of gravity).
• 1. Hips rotate along the spine axis with the legs.
  2. At the Passing Point, the free leg pulls the hips out of centre, rocking the hips side-to-side.
• Both of these motions are transmitted through the spine and shoulders (which mirror the hips motion) to maintain balance.
• The spine absorbs the shock transmitted to the hips.
• The head bobs around slightly to stay balanced.
• Add Personality by adding a swing to the hips - this tends to look more feminine.

Arms

• When walking, the arms act like a pendulum, dragging a few frames behind the hips and shoulders. And like the legs, ensure that the arms are always slightly bent.
• Add Personality by adding purpose to the swing (think of the way your arms move when you're in a rush, sad or happy).

2. Controlling Movement

2.1 Multiple Characters

Walk cycles often appear repetitive and lifeless, especially when multiple characters have the same walk cycle (appears robot-like). And normal walk cycle work well only on level terrain.

Solution: Stagger the walk cycle of different characters and give them all different gaits by varying the frames per step, and stride and leg length.

2.2 Motion Transitions

Walk to Run vs. Run to Walk

• Walk to Run: Your body leans forward and the forward knee bends as the body prepares for a leap. Then the body straightens out in the 1^st step of the run.
• Run to Walk: In the last step of the run, the shoulders move back and the hips pivot forward and the knees absorb the shock of the impact. As the energy dissapates, the body slows to a walk.

Turning

• Turns are created by turning the hips and feet with each successive step. The shoulders will lean slightly towards the turn.

Going Up and Down Slopes

• Uphill: You need to maintain relatively vertical stance so the upper body leans forward. Because you're exerting more energy (blame gravity), your knee bend more and the timing of the walk is affected.
• Downhill: The upper body leans back slightly and the arms stay out to maintain balance (walk down a hill with your arms across your chest to see the difference). The knees bend to absorb the shock and the timing of the walk is affected.