Rick Parent – CSE788 Modeling Skin Blend using multiple bones Continuous Skin Separate object(s)...
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Transcript of Rick Parent – CSE788 Modeling Skin Blend using multiple bones Continuous Skin Separate object(s)...
Rick Parent – CSE788
Modeling Skin
Blend using multiple bones
Continuous Skin
Separate object(s) per limb (and joints)
Rigidly transform vertices
Transform vertices between bisectors
Pose space deformations
Wrap skin around model of internal structure
Rick Parent – CSE788
Separate objects
Overlapping gives appearance of continuous surface - somewhat
Add element at joint to smooth between limbs
Works best with uniform color
Rick Parent – CSE788
Continuous skin
Define underlying skeleton from skin
Design character skin
Bind skin vertex to skeleton
Rick Parent – CSE788
Rigidly bind vertex to closest bone
Skin vertex
Associate vertex with closest ‘bone’
Closest bone
Rigidly transform vertex as bone transforms
Rick Parent – CSE788
Rigidly transform vertices
Problems with overlap and stretching
Rick Parent – CSE788
Bind vertex to bone - bisectors
Skin vertex
Locate vertex relative to closest bone
p1p2
p0
Joint bisectors
12
12
01
01
pp
pp
pp
ppn
Normal of bisecting plane
12
)12()1(
pp
pppvd
Distance from vertex to bone
d
Line parallel to bone through vertex
s
t
s – distance from vertex to first bisectort – distance between bisectors
v
Rick Parent – CSE788
Map vertices to relative location
Use d, s, t to reconstruct location of vertex relative to
bone
Rick Parent – CSE788
Bind vertex to multiple bones
Skin vertex
Locate vertex relative to closest bone
80%20%
User ‘paints’ which bones affect what vertices
Relative distance used to compute weights
Rick Parent – CSE788
Blend transformation of vertices
Vertices around joint are affected by both bones
vCv ii
Rick Parent – CSE788
But twists can collapse vertices
So add addition joints or use alternatives to linear blending
Rick Parent – CSE788
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/Courses/cs-838-2001/Students/lx/p2.htm
Rick Parent – CSE788
Use anatomy to model deep structure
What artists do
Skin wraps bones, muscles, tendons, subcutaneous tissue
Surface geometry affected by what’s happening underneath
Rick Parent – CSE788
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 – CSE788
Reference material
Artistic AnatomyAnatomy related to surface appearanceversus Medical AnatomyWell-developed literature
Forensic ScienceFacial Reconstruction
Plastic SurgerySurface Appearance Reconstruction
Rick Parent – CSE788
Layered: Bone-Muscle-Skin
Bone
Muscle &Tendons
Skin
Fatty Tissue
Rick Parent – CSE788
Modeling - Layered
FFD muslces
John Chadwick, ABDCSE OSU ‘90
Rick Parent – CSE788
Modeling - Thalmann, EPFL
From http://ligwww.epfl.ch/
Implicit surfaces
Rick Parent – CSE788
Modeling
Embed polyhedra in implicit surfaceImplicits used for approx. collision detect & respondPolyhedra used for display
Use M.-P. Cani technique to distort implicits based on collisions
Karan Singh, PhDCSE OSU ‘95
Rick Parent – CSE788
Human Figure
Use artistic anatomy to design muscles
Ferdi Scheepers, PhDCSE OSU ‘97
Rick Parent – CSE788
Human Figure
Rick Parent – CSE788
Human Figure
Rick Parent – CSE788
Figures - Wilhelms, UCSB
http://www.cse.ucsc.edu/~wilhelms/fauna/Monkeys/5monk_parts.gif
Rick Parent – CSE788
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/