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Download L18_ModelingSkin - Computer Science and Engineering
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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 Rick Parent - CIS682 Separate objects Overlapping gives appearance of continuous surface - somewhat Add element at joint to smooth between limbs Rick Parent - CIS682 Continuous skin Design character skin Define underlying skeleton from skin Bind skin vertex to skeleton Rick Parent - CIS682 Rigidly bind vertex to closest bone Skin vertex Closest bone Associate vertex with closest ‘bone’ Rigidly transform vertex as bone transforms Rick Parent - CIS682 Rigidly transform vertices Problems with overlap and stretching Rick Parent - CIS682 Bind vertex to bone - bisectors Locate vertex relative to closest bone Normal of bisecting plane p1 p0 p2 p1 n p1 p0 p2 p1 Skin vertex v s t d p2 p0 Distance from vertex to bone (v p1) ( p2 p1) d p2 p1 p1 Joint bisectors Line parallel to bone through vertex s – distance from vertex to first bisector t – distance between bisectors Rick Parent - CIS682 Map vertices to relative location Use d, s, t to reconstruct location of vertex relative to bone Rick Parent - CIS682 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 Rick Parent - CIS682 Blend transformation of vertices v i Ci v Vertices around joint are affected by both bones Rick Parent - CIS682 But twists can collapse vertices So add addition joints or use alternatives to linear blending Rick Parent - CIS682 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 Rick Parent - CIS682 Use anatomy to model deep structure What artists do Surface geometry affected by what’s happening underneath Skin wraps bones, muscles, tendons, subcutaneous tissue Rick Parent - CIS682 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 Rick Parent - CIS682 Reference material Artistic Anatomy Anatomy related to surface appearance versus Medical Anatomy Well-developed literature Forensic Science Facial Reconstruction Plastic Surgery Surface Appearance Reconstruction Rick Parent - CIS682 Layered: Bone-Muscle-Skin Muscle &Tendons Fatty Tissue Bone Skin Rick Parent - CIS682 Modeling Layered FFD muslces John Chadwick, ABD CSE OSU ‘90 Rick Parent - CIS682 Modeling - Thalmann, EPFL Implicit surfaces From http://ligwww.epfl.ch/ Rick Parent - CIS682 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 Rick Parent - CIS682 Human Figure Ferdi Scheepers, PhD CSE OSU ‘97 Use artistic anatomy to design muscles Rick Parent - CIS682 Human Figure Rick Parent - CIS682 Human Figure Rick Parent - CIS682 Figures - Wilhelms, UCSB http://www.cse.ucsc.edu/~wilhelms/fauna/Monkeys/5monk_parts.gif Rick Parent - CIS682 Use Visible Human dataset Skeletal Muscle Modeling Using a NURBSBased Finite Element Method www.digital-humans.org/Report2004/Documents/13-MuscleStressAndStrain.htm http://graphics.stanford.edu/~fedkiw/ Rick Parent - CIS682
