# TAMU CSCE 641 - motion editing (48 pages)

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- Pages:
- 48
- School:
- Texas A&M University
- Course:
- Csce 641 - Computer Graphics

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Motion Editing and Retargetting Jinxiang Chai Outline Motion editing video click here Motion retargeting video click here Required Readings Comparing Constraint Based Motion Editing Methods Retargeting Motion to New Characters Kinematic Motion Editing Goal Edit an input motion sequence to achiev e new goals specified by the user Kinematic Motion Editing Goal Edit an input motion sequence to satisfy achieve new goals specified by the user e g edit the motion to meet new constraints Kinematic Motion Editing Goal Edit an input motion sequence to satisfy achieve new goals specified by the user e g edit the motion to meet new constraints could be multiple constraints Toy Examples Edit 1D function to match user constraints m t Old motion M m t t 1 T t Toy Examples Edit 1D function to match user constraints m t Old motion M m t t 1 T t Toy Examples Edit 1D function to match user constraints could be multiple constraints m t Old motion M m t t 1 T t Toy Examples Edit 1D function to match user constraints could be multiple constraints m t Old motion m t t 1 T t So how can we generate a new motion M to satisfy new constraints c Toy Examples Idea 1 Modify the motion m t t 1 T using new co nstraints C M t Old motion m t t 1 T t Toy Examples Idea 1 Modify the motion m t t 1 T using new co nstraints C m t t Does this work Toy Examples Idea 1 Modify the motion m t t 1 T using new co nstraints C m t t Does this work probably not the new motion is not smooth Toy Examples Idea 1 Modify the motion m t t 1 T using new co nstraints C M t t Does this work probably not the new motion is not smooth filter the motion Toy Examples Idea 1 Modify the motion m t t 1 T using new co nstraints C Filter the edited motion M M t t Does this work probably no the new motion is not smooth filter the motion but the new motion now does not meet cons Toy Examples Idea 1 Modify the motion m t t 1 T using new co nstraints C Filter the edited motion M M t t Does this work probably no the new motion is not smooth filter the motion repeat modification and filtering process Idea 1 Modification Filter Another Example Three Constraints Another Example Three Constraints Idea 1 Summary Pros easy to implement computationally efficient Cons does not handle complex constraints e g constraint functions involved more than one frames m t e g m t1 m t2 5 Old motion M m t t 1 T t1 t2 t Idea 1 Summary Pros easy to implement computationally efficient Cons does not handle complex constraints e g constraint functions involved more than one frames How to address this limitation Idea 2 Constrained Optimization Modify the motion M to satisfy new constraint sC m t Old motion m t t 1 T t Idea 2 Constrained Optimization Modify the motion M to satisfy new constraint sC m t Old motion m t t 1 T t But this is an ill posed problem There are tons of solutions that satisfy the new constraints C Idea 2 Constrained Optimization Modify the motion M to satisfy new constraint sC m t Old motion m t t 1 T t But this is an ill posed problem There are tons of solutions that satisfy the new constraints C Remove the ambiguity by picking the solution with a minimal change across an entire motion Idea 2 Constrained Optimization Modify the motion M to satisfy new constraint sC m t Old motion m t t 1 T arg min m t t 1 T m t m t f M C 2 t Idea 2 Constrained Optimization Modify the motion M to satisfy new constraint sC m t Old motion m t t 1 T arg min m t t 1 T m t m t f M C 2 t Minimize the changes Satisfy new constraints Idea 2 Constrained Optimization We can also formulate this as an unconstraine d optimization problem m t Old motion m t t 1 T 2 t arg min m t t 1 T m t m t f M C 2 Idea 2 Constrained Optimization This is also called as spacetime optimization or trajectory optimization Simultaneously compute the entire motion m t Old motion m t t 1 T 2 t arg min m t t 1 T m t m t f M C 2 Idea 2 Constrained Optimization This is also called as spacetime optimization or trajectory optimization Simultaneously compute the entire motion m t Old motion m t t 1 T 2 t arg min m t t 1 T m t m t f M C 2 Now Back to Human Motion Editing Human motion representation A sequence of poses q1 q2 qT Each pose is represented as a high dimensional vector q t Rn Pose qt Motion q1 qT Motion trajectories Human Motion Editing Human motion is a high dimensional function Constraints could be any kinematic constraints User Constraints Any kinematic constraints throughout the motion Position cons Orientation cons Distance cons Joint angle cons Solution 1 Per frame IK Filtering Step 1 Per frame inverse kinematics to modify po ses in each frame with new constraints this might be ill posed remove ambiguity by minimizing the difference between old poses and new poses Step 2 motion filtering Repeat step 1 and 2 until the solution converges Solution 2 Spacetime Motion Editing Consider all constraints simultaneously Use optimization to solve the entire motion 2 arg min m t t 1 T m t m t f M C 2 Solution 2 Spacetime Motion Editing Consider all constraints simultaneously Use optimization to solve the entire motion 2 arg min m t t 1 T m t m t f M C 2 Currently minimizing joint angle poses across the entire sequence A better criterion is possible Solution 2 Spacetime Editing Better Criterion Geometric constraints such as contact constraints are often more important Solution 2 Spacetime Editing Better Criterion Frequency Content or details Solution 2 Spacetime Motion Editing 2 arg min m t t 1 T m t m t f M C 2 Implementation details use Spline representation to reduce the solution space often computationally expensive optimization over sub windows when working on a long motion sequence Motion Retargeting One motion a cast of characters Focus on similar structure Motion Retargeting Key Idea Formulated as motion editing problem 2 arg min m t t 1 T m t m t f M snew C Skeleton of new characters 2 Motion Retargeting Key Idea Step 1 Extract constraints properties C from source motion 2 arg min m t t 1 T m t m t f M snew C 2 Extracted constraints Motion Retargeting Key Idea Step 1 Extract constraints properties C from source motion 2 arg min m t t 1 T m t m t …

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