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Group Motion Editing

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SIGGRAPH 08

SIGGRAPH 08

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  • 1. SIGGRAPH 2008 Presented by Ting-sheng Lin Taesoo Kwon 1 1 Seoul National University Kang Hoon Lee 2 2 Kwangoon University Jehee Lee 3 3 Seoul National University Shigeo Takahashi 4 4 University of Tokyo
  • 2.
    • Introduction
    • Background
    • Graph Construction
    • Editing Group Motions
    • Stitching Group Motions
    • Postprocess
    • Experimental Results
    • Discussion
  • 3.  
  • 4.
  • 5.
    • Crowd Scenes
      • Feature animation films
      • Video game
    • State of the art
      • Simulating each individual that chooses its action
      • Rules, decision models, force fields
      • Careful parameter tuning
      • Lack precise control of individuals
      • Laborious trial and error
  • 6.
    • Interactive editing scheme
      • Complements such simulation-based techniques
      • Animators have direct control over animated crowd behaviors
      • Selectively edit and combine some portions of the simulation results to achieve globally satisfactory results
    • Manipulating the motion of multiple characters
      • Repositioning only a few characters
      • Preserve each individual trajectory and group formation of individuals
  • 7.
    • Novel graph structure
      • Each vertex : location of an individual at a sampled frame
      • Connecting edge : individual moving trajectories and neighborhood formation
    • Mesh editing method [Igarashi et al. 2005]
      • Deform a group motion
      • Stitch two independent group motions
      • Avoiding collisions
  • 8.  
  • 9.
    • Synthesizing realistic group
      • Agent models [Reynolds 1987; Musse and Thalmann 1997; Pelechano et al. 2005, Shao and Terzopoulos 2005]
      • Directly model [Chenney 2004, Hughes 2003; Treuille et al. 2006]
      • Data-driven method of constructing group behavior models [Lai et al. 2005; Lee et al. 2007; Lerner et al. 2007; Courth and Corpetti 2007; Paris et al. 2007]
  • 10.
    • Motion editing
      • Motion clips to be manipulated with constraints [Gleicher 1997; Lee and Shin 1999]
      • Concatenated [Rose et al. 1996]
      • Interpolated [Rose et al. 1998; Mukai and Kuriyama 2005]
      • Rearranged [Lee et al. 2002; Kovar et al. 2002; Arikan et al. 2003]
    • Our goal is to provide users with a similar level of flexibility in edition group motions
  • 11.
    • Our approach
      • Data-preserving shape editing [Igarashi et al. 2005]
      • Maintaining the local arrangement of vertices allows user to intuitively manipulate 2D and 3D shapes
      • As-Rigid-As-Possible Shape Manipulation [Igarashi et al. SIGGARPH 05]
  • 12.  
  • 13.
    • Large crowd animation
      • Tractable motion clips
      • Each group motion clip consists of a set two-dimensional moving trajectories of individual characters
      • Preserving spatial relations among individuals
  • 14.
    • .
    • Formation edge
      • Represent the neighborhood relationships between individuals
      • Challenge: correctly identify the formational relationships
        • Neighborhoods can vary according to time
        • Don’t keep pace with other characters and moves at variable speeds
      • Delaunay triangulation of vertices at each plane
    • Motion edge
      • Connect with the vertex of the corresponding character at the previous plane and next plane
  • 15.  
  • 16.
  • 17.
    • It is invariant on the uniform scaling of local features
      • Unnaturally enlarged , shrunken
    G G’
  • 18.
    • Two-step optimization scheme [Igarashi et al. 2005]
      • Step one: scale-free construction
      • Step two: scale adjustment
      • Graph undergoes a large deformation
        • Highly-distorted
        • Near-degenerate triangles
    • Group motion editing
      • Motion artifacts: sudden velocity changes
      • Spatial group formation: scale-adjustment
      • Temporal distortion: time-warping
  • 19.
    • We consider three types of triangular features
      • Spatial , temporal , spatiotemporal features
    V t V t+1 V t-1 w t s t u t V t V t+1 V t-1 w t s t u t V t V t+1 V t-1 w t s t u t
  • 20.
      • Spatial feature
    temporal feature spatiotemporal feature
  • 21.
    • Only the spatial features are scaled
    • Construct a spare linear system that can solve E 1 and E 2
      • Variable elimination [Igarashi et al. 2005]
      • Lagrange multiplier scheme
  • 22.  
  • 23.
    • G and G’ having the same number of individuals N
    • Stitching two graphs requires three steps
    • First step
    Bipartite graph matching algorithm [Belongie et al. 2002] G G’ G G’
  • 24.
    • Second step
    • Final step: smoothly morphing group formations
      • Linear blending don’t generate desired results
      • We blend triangular (spatial, temporal, spatiotemporal)
    Aligned two motion clips by translating and rotating them to best match the boundary [Kovar et al. 2002] G’’ G G’
  • 25.  
  • 26.
    • Deformation or stitching of a group motion
      • Collision , insufficient clearance
      • Collision avoidance algorithm: approximate and iterative method
      • Certain threshold : two trajectories
      • Pulls the trajectories away by 10% of the threshold and repeats this process until all collision are resolved
    • Avoid collision with obstacles
      • We pull the deepest penetrating point toward the nearest point on the boundary of the obstacle
  • 27.
    • This speed change is often irregular
      • Irregular speed change is usually undesirable in motion editing
      • Time warping
  • 28.  
  • 29. 1. Battle field scene 2. Downtown scene
  • 30.  
  • 31.
    • Conclusions
      • Animators to manipulate existing group motion data interactively
      • Detail-preserving approach
      • Advantage: direct, precise control
    • Limitations
      • Cannot large deformation, but lead to unnatural speedup/slowdown
      • Cannot handle a large crowd consisting of thousands character
    • Future work
      • Deal with a wider variety of group behaviors (e.g: chatting, Olympic …)