1. Spring 2014 CS274: Automatic Rigging
Zhinan Xu, Tianyuan Qin, Yue Liu

2. Motivation

3. Algorithm Overview Primary 3D Silhouette Detection
global search, local search
Curve Skeleton Extraction
triangulation, pruning, joint detection
Animation Skeleton Generation
decomposition, refinement
Skin Attachment
skeleton hierarchical movement
skin transformation interpolation

4. Primary 3D Silhouette Detection
Global Search:
Project all points to a 2D plane
Find the 2D silhouette using a process similar to Jarvis’ March for convex hull computation
Local Search:
Connect all vertices according to the connectivity of the original 3D mesh model.

5. Curve Skeleton Extraction
Triangulation
Perform constrained Delaunay triangulation on 2D silhouette.
Extract the 2D medial axes.
Generate 3D medial axes from the 2D medial axes coupled with depth information which is interpolated from the 3D silhouette.

6. Triangle Pruning

7. Prune & Joint detection
Terminal Prune (cryan line)
iteration
Junction Prune
BFS
Joint Detection(red point)
local minimal
Branch Connection
straight skeleton

8. Curve Skeleton Extraction
Decomposition
Medial axes generated from the previous step are separated to different branches.
Assign vertices on the mesh to different groups base on their distance to each branches.
Each branch now has a group of vertices belongs to it.

9. Curve Skeleton Extraction
Curve Skeleton Refinement
Depth information of the branches is not accurate.
For each part, find a second projection plane that is perpendicular to the first projection plane.
Construct another 3D silhouette based on the second projection.
Adjust the depth of the branch base on it distance to the second silhouette
Smooth the branches to get the curve skeleton

11. Animation Skeleton Generation
Generate Skeleton Hierarchy
Refined joint position
Connection information
Calculate the mass center joint as root
Generate hierarchy starting from root with DFS
Father
Child
Grandchild
Rotate Hierarchy

12. Skin Attachment Linear Blend Skinning
Find joints related to the skin vertices with weight
Interpolate the joint transformations as vertices transformation
Control them with UI

13. Result by demo

14. Implemenetation
Language: C++
Libraries:
OpenGL, OpenMesh, Face2D, Qt.

15. Future Work Algorithm Limitations Future Work
Models need to be fully extended
Algorithm is too sensitive to the occlusion
Linear blend skinning causes lots of artifact
Future Work
Instead of forward kinematics, implement inverse kinematics
Implement dual quaternion skinning

16. Questions ???

17. Thank you!!!