El mundo de la computacion grafica

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Computer Animation Where we are (overview) Where
we are going (perhaps)
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Animation overview
Computer Animation
Popular perception - CGI is animation (full
length animations, CGI effects films or computer
games).
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Animation overview
Off-line/pre-recorded Animation is expensive
Production effort same as handmade
animation   The Fox and the Hound Toy Story
(1)   Time 4 years 4 years (1.5 story 2.5
production) Frames 110,000 110,064 Time
2.9 hours/frame 45mins-24hrs/frame Paint
450 gallons 110 SUNs
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Animation overview
Real-time Computer Animation in Games

• Animation control (script) in games is
• pre-recorded (MOCAP) or pre-designed (currently
  the de facto standard in games)
• calculated in real time
• (IK and dynamics)
• a mix of pre-recorded and real time

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Animation overview
MOCAP in Games is select and blend
Game events
Animate skeleton
MoCap 1
skin
Render
MoCap 2
For example a football game will have 200-300
sequences.
MoCap n
MoCap X
blend
MoCap Y
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Animation overview
Script creation methods
? Recording real motion (MOCAP) 1st ? By
hand using proprietary or in-house software,
keyframe animation 1st ? Posing real motion
using a digital input device (DID) (film special
effects) ? Executing dynamic equations
(scientific visualisation, computer games) ?
Behaviour models (film special effects)
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Animation overview
Script creation -Motion quality-best is MOCAP
Animación (portero)
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Animation overview
Script creation -Motion quality-best is MOCAP
z
x
Hombro 3 DOFs
y
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Animation overview
Script creation -Motion quality-best is MOCAP
Applying MOCAP to a skeleton
y
y
x
x
z
z
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Animation overview
Motion Capture quality motion is always
perceivable as such (even with stick figures)
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Animation overview
MOCAP-bones-skinning is a well-established
technology
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Animation overview
Script creation
 By hand using proprietary or in-house
software. The most popular method is keyframe
animation.
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Animation overview
Real time dynamics
Executing dynamic equations (computer games,
scientific visualisation) Flong Ftraction
Fdrag a F/m v v dta p p dtv
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Animation overview
Script creation methods
High level behavioural models original was
flocking
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Animation overview
Script creation methods
Posing real motion - stop motion animation was
used in Jurassic Park (Dinosaur Input Device) to
script the computer models
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Animation overview
Animation in Science
Zajac 1966 Bell Telephone Lab First Computer
animation in science
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Animation overview
Animation in Science
Max Born 1935
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Animation overview
Animation in Science
Max Born 1935 The Restless Universe
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Animation overview
Animation in Science

• Muscle Fibres of the heart

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Animation overview
Forensic Animation - ethics?
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Animation overview
Forensic Animation ethics?

• Technology blesses the production with veracity?
• Who controls the content of simulation?
• How can the accuracy be guaranteed?
• No cross examination possible

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Animation overview
Synthetic vision

• Provides a synthetic view of reality,
  constructed from a database, which cannot be seen
  because of, for example, weather conditions. The
  best example is civil aviation.
• Principles used are exactlty the same as games
  where a view frustum is driven through an
  environment under user control.

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Animation overview
Synthetic vision in civil aviation

• Cockpit view

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Animation overview
Synthetic vision in civil aviation

• Landing display

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Animation overview
Synthetic vision in civil aviation

• Uses as database
• Shuttle Radar Topography Mission (SRTM)
• Wide Area Augmentation System (WASS)
• Local Area Augmentation System (LASS)
• Derives 3D position (Accuracy lt 1m) from
• GPS INS
• On-board sensors (such as RADAR altimeters)

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Animation overview
Synthetic vision in civil aviation

• Animation of an approach

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Animation overview
Where we are

• Off-line -manual
• Combining off-line event driven
• Event driven dynamic simulations walk
  throughs

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Animation overview
The future ?

• Whats wrong with MOCAP
• Although pre-reorded aninimation is of high
  quality, it is inherently
• limited the more complex the game the more
  clips are required.
• Cannot MOCAP animals.
• MOCAP transitions blending is unsatifactory
• What we would like
• Increase the quality of real-time animation and
  obtain any motion in
• real time accoording to the action demand
  event driven
• Speech/emotion expression needs to be event
  driven

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Event driven animation for humanoids
What we have now event driven recorded animation
Game events
Animate skeleton
MoCap 1
skin
Render
MoCap 2
This model can only react to completely
pre-determined actions
MoCap n
MoCap X
blend
MoCap Y
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Event driven animation for humanoids
What we have now- MOCAP more general
One generic motion fits all characters
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Event driven animation for humanoids
Why do we need it?
Important element in an anthropomorphic interface
computer vision
camera
speech recogn.
NLP
query system
game
text generatn.
visual speech
expressn
emotion generatn.
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Event driven animation for humanoids
What do we aim for

• Seems sensible to retain MOCAP technology high
  quality, well established so increase its
  flexibility - adaptation
• BUT oranges are not the only fruit. Can we
  generate animation in real time.

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Event driven animation for humanoids
Examples

• Using IK adapted MOCAP in human motion
• Total IK solution for human motion
• Using MOCAP in visual speech
• total solution for visual speech

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Event driven animation for humanoids
Character adaptation not straight forward

• Change scale joint angles change in non-linear
  manner

From Shin et al 2001
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Event driven animation for humanoids
Cheating for real-time
Use v.simple skeleton and complex skin. C.G
skeletons 50 DOFs human skeletons - gt250
DOFs Motion from skeleton, visual complexity from
skin
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Event driven animation for humanoids
MOCAP is forward kinematics
Motion of end effector
f(
)
MOCAP
)
X
f(
q
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Event driven animation for humanoids
Inverse Kinematics an old idea
Circa 1985
use for complete soln. use to adapt MOCAP
x f (?)
Forward Kinematics
joint space ?
Cartesian space x
? f-1 (x)
Inverse Kinematics
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Event driven animation for humanoids
Inverse Kinematics solutions

• Geometric/Analytical This class of solvers
  generate a solution in a single step for a given
  goal and therefore fast. They can be used as
  part of a solution in a hybrid method.
• Differential Algorithms The task is transformed
  into a linear problem based on small changes
  using the Jacobian and iteratively refining the
  system to meet the goal position.
• Cyclic Co-ordinate Descent An algorithm which
  again moves towards a solution in small steps.
  This time, however, the steps are formed
  heuristically.
• Hybrid Methods Uses a combination of
  approaches. Their motivation is usually real-time
  performance.

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Event driven animation for humanoids
Differential IK the Jacobian
The Jacobian is the multidimensional extension to
differentiation of a single variable. Given a
function X f(?) where X is of dimension n
and ? of dimension m, the Jacobian J is the n x m
matrix of partial derivatives relating
differential changes of ?, to differential
changes in X, written as dX J(?)d? ? d?
J-1(?)dX where the (i, j)th element of J is given
by Jij ?fi/??j
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Event driven animation for humanoids
Event driven animation for humanoids
Inverse Kinematics an old idea
Differential IK - iteration

• Calculate the incremental step ?X Xgoal X
• Calculate the Jacobian matrix using the current
  joint angles
• Calculate the inverse of the Jacobian using
  right-hand generalised inverse if required J-1
  JT(JJT)-1
• Check for iterative convergence i.e. make sure
  the Jacobian inverse is suitably accurate
• (a) If (I JJ-1) gt e, reduce ?X?X/2 and
  repeat 4 (where e is a convergence threshold)
• (b) If (I JJ-1) gt e after a number of
  steps then the goal is likely out of reach so
  terminate
• Calculate the updated values for the joint angles
  where ? ?J-1?X
• Using forward kinematics to determine whether the
  solution is close enough to the goal. If the
  solution is adequate then terminate iteration
  else go back to step 1 (as step 4 could have
  reduced ?X).

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Event driven animation for humanoids
Event driven animation for humanoids
Inverse Kinematics an old idea
Differential IK example Jacobian
Determining the Jacobian Consider
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Event driven animation for humanoids
Event driven animation for humanoids
Inverse Kinematics an old idea
Differential IK example Jacobian
where
?
?
?
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Event driven animation for humanoids
Differential IK the Jacobian

• For large articulations the complexity of
  analytically expressing the differentiation is
  very tedious.
• The Jacobian can be viewed as expressing the
  velocity of the end of the chain in terms of
  local angular velocities with respect to a base
  frame.
• This information is easily extracted from
  transformation matrices that already exist in the
  graphics pipeline i.e. the matrix concatenation
  of child-parent relationships as the articulation
  is built up.
• When the Jacobian is not square (whenever the
  number of DOFs in the chain increase past the
  dimension of the end-effector), a pseudo-inverse
  is required, which could lead to numerical error.
• Singularities a decrease in the rank of the
  Jacobian can result in the loss of a degree of
  freedom that usually happens when the chain is
  fully extended

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Event driven animation for humanoids
Differential IK- main problem

• Underdetermined System
• The purpose of Inverse kinematics is to produce
  a set of joint angles that allows an end-effector
  to be positioned in a given location. This is an
  underdetermined system therefore many solutions
  exist.

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Event driven animation for humanoids
Differential IK- joint constraints

• Removal of redundant DOFs from the Jacobian
• Angular Constraints Modification of step 5 of
  the iterative algorithm to include boundary
  constraints on specified DOFs
• ? lower bound if ?J-1?P lt lower bound
• upper bound if ?J-1?P gt upper bound
• ?J-1?P otherwise

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Event driven animation for humanoids
Differential IK- demo
Unconstrained IK chain
Constrained IK chain
0??0?180 0??1?90 -30??2?30 -18??3?-18
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Event driven animation for humanoids
Differential IK- MOCAP adaptation
Change scale joint angles change in non-linear
manner
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Event driven animation for humanoids
Differential IK- MOCAP adaptation
Retargetting by simply scaling
Retargetting using IK constraints to maintain
foot plants
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Event driven animation for humanoids
Differential IK
Scaled Retargetting IK Retargetting to
maintain foot plants
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Event driven animation for humanoids
Differential IK- total solution-walking
Foot flight curve
(a) (b) (a)
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Event driven animation for humanoids
Differential IK- main problem
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Event driven animation for humanoids
Facial Animation two level model

• Apply motion to bones which control the skin
• Motivation is identical script applied to
  bones and bones control face vertices
• No. of bones 2-3 orders of magnitude less than
  face vertices

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Event driven animation for humanoids
Facial Animation two level model - muscles
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Event driven animation for humanoids
MOCAP concatenating
text
Blahblahblahblahblah
phonemes
visemes
Muscle values
Keys and interpolate
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Event driven animation for humanoids
Facial Animation muscles problem?
Interpolating between static targets does NOT
produce convincing mouth motion
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Event driven animation for humanoids
Facial Animation two level - bones
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Event driven animation for humanoids
Facial Animation two level - bones
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Event driven animation for humanoids
Facial Animation bones problem?
Incapable of particularly subtle expressions and
so unsuitable for expressive speech
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Event driven animation for humanoids
Facial Animation visual speech

• MOCAP can be used to
• Cure subtlety problem
• Implement general domain speech by
  concatenation
• BUT
• How do we retarget? Face changes both scale and
  shape
• How do we concatenate motion? will conventional
  blending work?

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Event driven animation for humanoids
MOCAP mesh control from sparse markers
SOFFD mesh from markers
MOCAP markers
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Event driven animation for humanoids
MOCAP mesh control from sparse markers
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2) Deform reference mesh to fit target mesh
2
1
3

1. Position markers on reference mesh to define a
   control surface - 667 for head motion

3) Retargetted control surface
MOCAP retargetting
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Event driven animation for humanoids
MOCAP retargetting
Marker motion
speech
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Event driven animation for humanoids
MOCAP retargetting
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Event driven animation for humanoids
MOCAP retargetting
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Event driven animation for humanoids
MOCAP for visual speech

• Can use variable length fragments (sentences,
  words or syllables)
• Overcomes the co-articulation problem
• Conventional blending seems to work

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Event driven animation for humanoids
MOCAP concatenating
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Event driven animation for humanoids
MOCAP concatenating

• So is MOCAP speech the answer? NO
• Because
• The inherent quality advantage derives from using
  variable length units (sentences, phrases, words)
  and this would demand masses of data for general
  domain speech.
• Expressive speech? E.g combine a smile with an
  utterance.

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Event driven animation for humanoids
Facial Animation the return of static phonemes
text
Phonemes/visemes as static a units are a good
solution for general domain speech Can we do
better than interpolation?
Blahblahblahblahblah
phonemes
visemes
Muscle values
Keys and interpolate
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Event driven animation for humanoids
Facial Animation the return of static phonemes
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Event driven animation for humanoids
Facial Animation constraint based global
solution

• Treat V as a point in 13D space
• Assign a weight/dominance to each V
• For each unit (sentence) find a global solution
  a trajectory through this space
• Solution does NOT interpolate the means exactly

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Event driven animation for humanoids
Facial Animation the return of static phonemes
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Event driven animation for humanoids
Facial Animation the return of static phonemes
Decreasing the dominance of the 4th segment
reduces its effect over the entire trajectory
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Acknowledgments/contacts Mocap/inverse
kinematics m.meredith_at_dcs.shef.ac.uk Visual
speech j.edge_at_dcs.shef.ac.uk