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Modeling Skin

Modeling Skin. Separate object(s) per limb (and joints). Continuous Skin. Rigidly transform vertices. Transform vertices between bisectors. Blend using multiple bones. Pose space deformations. Wrap skin around model of internal structure. Separate objects.

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Modeling Skin

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  1. Modeling Skin Separate object(s) per limb (and joints) Continuous Skin Rigidly transform vertices Transform vertices between bisectors Blend using multiple bones Pose space deformations Wrap skin around model of internal structure

  2. Separate objects Overlapping gives appearance of continuous surface - somewhat Add element at joint to smooth between limbs

  3. Design character skin Define underlying skeleton from skin Continuous skin Bind skin vertex to skeleton

  4. Rigidly bind vertex to closest bone Skin vertex Closest bone Associate vertex with closest ‘bone’ Rigidly transform vertex as bone transforms

  5. Problems with overlap and stretching Rigidly transform vertices

  6. Normal of bisecting plane t s d Joint bisectors Distance from vertex to bone Line parallel to bone through vertex s – distance from vertex to first bisector t – distance between bisectors Bind vertex to bone - bisectors Locate vertex relative to closest bone Skin vertex v p2 p0 p1

  7. Map vertices to relative location Use d, s, t to reconstruct location of vertex relative to bone

  8. Bind vertex to multiple bones Locate vertex relative to closest bone Skin vertex 20% 80% User ‘paints’ which bones affect what vertices Relative distance used to compute weights

  9. Vertices around joint are affected by both bones Blend transformation of vertices

  10. But twists can collapse vertices So add addition joints or use alternatives to linear blending

  11. Pose space deformations User ‘sculpts’ skin in various poses For each vertex solve weights to use with Radial Basis Functions for scattered data interpolation See: www.cs.wisc.edu/graphics/Course/cs-838-2001/Students/tx/p2.htm

  12. Use anatomy to model deep structure What artists do Surface geometry affected by what’s happening underneath Skin wraps bones, muscles, tendons, subcutaneous tissue

  13. Warp skin based on model of internal structure Skeletal articulation modifies shape of muscle Muscle shape modifies skin shape Add model of tendons, fatty tissue

  14. Reference material • Artistic Anatomy • Anatomy related to surface appearance • versus Medical Anatomy • Well-developed literature • Forensic Science • Facial Reconstruction • Plastic Surgery • Surface Appearance Reconstruction

  15. Layered: Bone-Muscle-Skin Muscle &Tendons Fatty Tissue Bone Skin

  16. Modeling - • Layered FFD muslces John Chadwick, ABD CSE OSU ‘90

  17. Modeling - Thalmann, EPFL Implicit surfaces From http://ligwww.epfl.ch/

  18. Modeling • Embed polyhedra in implicit surface • Implicits used for approx. collision detect & respond • Polyhedra used for display Use M.-P. Cani technique to distort implicits based on collisions Karan Singh, PhD CSE OSU ‘95

  19. Human Figure Ferdi Scheepers, PhD CSE OSU ‘97 Use artistic anatomy to design muscles

  20. Human Figure

  21. Human Figure

  22. Figures - Wilhelms, UCSB http://www.cse.ucsc.edu/~wilhelms/fauna/Monkeys/5monk_parts.gif

  23. Use Visible Human dataset Skeletal Muscle Modeling Using a NURBS-Based Finite Element Method www.digital-humans.org/Report2004/Documents/13-MuscleStressAndStrain.htm http://graphics.stanford.edu/~fedkiw/

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