We combine the often opposing forces of artistic freedom and mathematical determinism to enrich a given animation or simulation of a surface with physically based detail. We present a process called tracking, which takes as input a rough animation or simulation and enhances it with physically simulated detail. Building on the foundation of constrained Lagrangian mechanics, we propose weak-form constraints for tracking the input motion. This method allows the artist to choose where to add details such as characteristic wrinkles and folds of various thin shell materials and dynamicaleffects of physical forces. We demonstrate multiple applications ranging from enhancing an artist's animated character to guiding a simulated inanimate object.


"TRACKS: Toward Directable Thin Shells"
Miklós Bergou, Saurabh Mathur, Max Wardetzky, Eitan Grinspun
ACM Transactions on Graphics (SIGGRAPH) 2007
[PDF] [Errata]
         title = {{TRACKS: Toward Directable Thin Shells}},
         author = {Mikl{\'{o}}s Bergou and Saurabh Mathur and Max Wardetzky and Eitan Grinspun},
         journal = {ACM Transactions on Graphics (SIGGRAPH)},
         volume = {26},
         number = {3},
         pages = {50:1--50:10},
         year = {2007},
         month = {jul}


You can download the PowerPoint presentation along with all of the movies that was shown at SIGGRAPH 2007. Please feel free to use any of the material, but make sure to give credit where it is due.
[PowerPoint slides]


These images show the results obtained from applying our framework to motion-capture data of a backflip. We apply the motion-capture data to a coarse mesh of a bag (top-left), and run our simulator with a variety of different parameters to achieve many different looks while maintaining the coarse shape.


Here are some datasets containing .obj files of the images seen in the paper. Feel free to use them as you wish.
[Backflipping bags] [Twisting boxes] [Xavier]


This video presents a brief overview of the capabilities of a tracking solver.

This video shows some additional results obtained with our solver.