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
Works best with uniform color

3. Bind skin vertex to skeleton
Continuous skin
Design character skin
Define underlying skeleton from 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
Problems with overlap and stretching

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

7. Use d, s, t to reconstruct location of vertex relative to bone
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
Vertices around joint are affected by both bones

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

11. See: www.cs.wisc.edu/graphics/Courses/cs-838-2001/Students/lx/p2.htm
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:

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

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

23. Use Visible Human dataset
Skeletal Muscle Modeling Using a NURBS-Based Finite Element Method