Adapting Motion Capture Data to Follow Adapting Motion Capture Data to Follow an Arbitrary Pathan Arbitrary Path

Presented by Mark WhitfieldSupervisors: Shaun Bangay and Adele Lobb

ProblemProblem

Avatar must follow an arbitrary path in a Avatar must follow an arbitrary path in a realistic fashionrealistic fashion

Why use motion capture?Why use motion capture?

Motion capture expensiveMotion capture expensive

OverviewOverview

Schools of thoughtSchools of thought

BVH filesBVH files

Motion path editingMotion path editing PathsPaths ResidualsResiduals Arc-length ReparameterizationArc-length Reparameterization

ResultsResults

DemonstrationDemonstration

QuestionsQuestions

3 Schools of Thought3 Schools of Thought

Alter a base motionAlter a base motion

Synthesize a new motionSynthesize a new motion

Cyclic MotionsCyclic Motions

BioVision Hierarchical (BVH) FilesBioVision Hierarchical (BVH) Files

Motion Path EditingMotion Path Editing

Altering a base motionAltering a base motion

Path is an abstraction of the motionPath is an abstraction of the motion

Motion represented relative to the pathMotion represented relative to the path

Alter path Alter path →→ alter motion alter motion

Creating the Initial PathCreating the Initial Path

Initial path is created using a least squares fit of the root Initial path is created using a least squares fit of the root node translation datanode translation dataInitialPath(t) = point (x(t), y(t), z(t))InitialPath(t) = point (x(t), y(t), z(t))

x

t

ResidualsResiduals

Original path (left)Original path (left)Adapted path (right)Adapted path (right)

ResidualsResiduals

Original path and motion (left)Original path and motion (left)Adapted path and motion when residuals represented Adapted path and motion when residuals represented absolutely (centre)absolutely (centre)Adapted path and motion when residuals represented Adapted path and motion when residuals represented relative to the path (right)relative to the path (right)

Moving Co-Ordinate SystemMoving Co-Ordinate System

Y-Up moving co-ordinate systemY-Up moving co-ordinate system

Z axis points in the direction of the tangent Z axis points in the direction of the tangent projected on the horizontalprojected on the horizontal

X axis is their cross productX axis is their cross product

Transform using the residuals in the Transform using the residuals in the moving co-ordinate systemmoving co-ordinate system

Then place this co-ordinate system in the Then place this co-ordinate system in the world co-ordinate systemworld co-ordinate system

Moving Co-Ordinate SystemMoving Co-Ordinate System

•Apply residuals in the moving co-ordinate system

Moving Co-Ordinate SystemMoving Co-Ordinate System

Moving Co-Ordinate SystemMoving Co-Ordinate System

Moving Co-Ordinate SystemMoving Co-Ordinate System

Tangent Vector Projected on HorizontalTangent Vector Projected on Horizontal

•Original path and motion •Adapted path with motion represented relative to the tangent

•Adapted path with motion represented relative to the tangent projected on the horizontal

Arc-Length ReparameterizationArc-Length Reparameterization

Altering the path may also alter the speed of the avatar.

The arc-length of frame f is the distance along the path from the start of the path to the position on the path at frame f.

Frame f in the new path must have the same arc-length as frame f in the original path.

Arc-Length ReparameterizationArc-Length Reparameterization

•Original path on the left•Adapted path on the right•Not using arc-length reparameterization

•Original path on the left•Adapted path on the right•Using arc-length reparameterization

Shorter and Longer PathsShorter and Longer Paths

End of path handlingEnd of path handling

CyclingCycling

ResultsResults

This technique is successful adapting This technique is successful adapting motion capture data to follow an arbitrary motion capture data to follow an arbitrary pathpath

The adapted motion does not look 100% The adapted motion does not look 100% realisticrealistic

FootskateFootskate

Constraints were not implementedConstraints were not implemented

Future WorkFuture Work

Implement constraints Implement constraints

Adapt the motion for avatars of different Adapt the motion for avatars of different sizesize

Multiple avatars which all have paths Multiple avatars which all have paths assigned to them. Implement collision assigned to them. Implement collision detection and resolution for the avatarsdetection and resolution for the avatars

DEMONSTRATIONDEMONSTRATION