1. Hair and strand-like deformable models 15-863: Class #15 (Mar 11) Doug James, CMU

2. Overview Class #15 (Mar 11) Course project & proposal Strand-like deformable models –Hair, sutures, cables, and other 1D structures –Flexible chains geometrically large deformation –Twist DOF makes things more interesting

3. Project Proposal 2 pages or less Use SIGGRAPH style LaTeX formatting http://www.siggraph.org/publications/instructions Proposal section structure: 1.Abstract 2.Introduction (What, why, related work) 3.Details of approach 4.Proposed work (incrementally defined) 1.Will do (core material) 2.Hope to do (time-permitting) 3.Ultimately would like to do (if 1 & 2 get done) 5.Summary of proposed contributions 6.References (e.g., use BibTeX & graphbib)

4. Project Calendar Proposal: Thursday, March 20. Progress report: Tuesday, April 15. Presentation: Thursday, April 24(?) Final report: Tuesday, April 29. ACM I3D: Away Tu-April 29 & Th-May 1.

5. Project Software Don’t have to reinvent the wheel Can explore PBMIS applications versus modeling fundamentals FEM, BEM, rigid bodies, collision detection, my code, etc. Constraint: project must be substantial

6. Possible evaluation choice OPTION A 30% - 2 assignments 60% - project 10% - presentation OPTION B 45% - 3 assignments 45% - project 10% - presentation

7. Strand-like deformable models Hair, sutures, cables, and other 1D structures Flexible chains –geometrically large deformation Twist DOF makes things more interesting Application determines utility of physically based models

8. Interactive Multiresolution Hair Modeling and Editing Tae-Yong Kim, Ulrich Neumann. ACM Transactions on Graphics. 21(3), pp. 620-629, 2002. Sometimes physics just gets in the way Hairstyling doesn’t require physically accurate hair Good survey: –N.Magnenat-Thalmann, S.Hadap, P.Kalra, State of the Art in Hair Simulation, International Workshop on Human Modeling and Animation, Seoul, Korea, Korea Computer Graphics Society, pp. 3-9, June, 2002.State of the Art in Hair Simulation

9. Interactive Multiresolution Hair Modeling and Editing Tae-Yong Kim, Ulrich Neumann. ACM Transactions on Graphics. 21(3), pp. 620-629, 2002.

10. Faking Dynamics of Ropes and Springs Ronen Barzel. IEEE Computer Graphics & Applications. 17(3), pp. 31-39, 1997. Animator key frames amplitudes of shape functions

11. Faking Dynamics of Ropes and Springs Ronen Barzel. IEEE Computer Graphics & Applications. 17(3), pp. 31-39, 1997.

13. Recall...

19. Some other approaches Could add torsional springs –[Rosenblum et al. 91] –[Daldegan et al. 93] Simulated Knot Tying. J.M. Phillips, A.M. Ladd, L.E. Kavraki. IEEE International Conference on Robotics and Automation 2002.Simulated Knot Tying See webpage for more examples. From [Hadap and Magnenat-Thalmann 01]

20. Open Kinematic Chains Hair is basically inextensible  numerical stiffness Multibody open chain approx. is now common for hair Can be solved efficiently Articulated-Body Method –Reduced coordinate formulation –O(n) forward dynamics –Featherstone, R., Robot Dynamics Algorithms, Kluwer, Boston, 1987. Could (of course) use fast O(n) Lagrange multiplier methods

21. A Practical Model for Hair Mutual Interactions Johnny T. Chang, Jingyi Jin, Yizhou Yu. ACM SIGGRAPH Symp. on Computer Animation. pp. 73-80, 2002. Recent example “Static links” Hair-hair interactions Hair interpolated using guide hairs Use Featherstone’s algorithm

22. A Practical Model for Hair Mutual Interactions Johnny T. Chang, Jingyi Jin, Yizhou Yu. ACM SIGGRAPH Symp. on Computer Animation. pp. 73-80, 2002.

26. Eric Plante, Marie-Paule Cani, Pierre Poulin, Capturing the Complexity of Hair Motion, GMOD numéro 1 volume 64, january 2002. Capturing the Complexity of Hair Motion

27. Next class... Thursday, March 13 Fast and Flexible 3D Scanning Szymon Rusinkiewicz, Princeton University Wean Hall 4623, Talk 12:30pm - 2:00pm The digitization of the 3D shape of real objects is a rapidly expanding field, with applications in design, manufacturing, and mapping spaces such as buildings and caves. This talk will describe recent research aimed at increasing the speed and flexibility of 3D scanning systems. Two new scanner designs will be presented, one based on active temporal stereo and the other based on projected structured light with stripe boundary coding. Both are based on a space-time stereo framework, in which correspondences between two cameras or between a camera and projector are obtained by considering windows with extent in both space and time. The scanners are the first stage in a 3D model acquisition pipeline, which also includes algorithms for aligning and merging successive range images. The talk will discuss the value of having the entire pipeline operate in real time, which allows the user to see holes in the model and determine when the object has been completely covered. Results are presented from a prototype that incorporates 60 Hz. structured-light rangefinder, a real- time variant of ICP (iterative closest points) for alignment, and point-based merging and rendering algorithms.

28. D. K. Pai, STRANDS: Interactive Simulation of Thin Solids using Cosserat Models, Computer Graphics Forum, 21(3), pp. 347-352, 2002.