S. Kircher and M. Garland. Free-Form Motion processing. ACM Transactions on Graphics, 27(2):1-13, April 2008. [Preprint (PDF)] [Movie (34MB MPEG4)] [Movie (40MB WMV)]

Motion is the center of attention in many applications of computer graphics. Skeletal motion for articulated characters can be processed and altered in a great variety of ways to increase the versatility of each motion clip. However, analogous techniques have not yet been developed for free-form deforming surfaces like cloth and faces. Given the time consuming nature of producing each free-form motion clip, the ability to alter and reuse free-form motion would be very desirable. We present a novel method for processing free-form motion that opens up a broad range of possible motion alterations, including motion blending, keyframe insertion, and temporal signal processing. Our method is based on a simple, yet powerful, differential surface representation that is invariant under rotation and translation, and which is well suited for surface editing in both space and time.

S. Kircher. Approximating, Editing, and Processing Free-Form Motion. Ph.D. Dissertation, Computer Science Department, University of Illinois at Urbana-Champaign. UIUCDCS-R-2007-2821. May 2007. [Online (97MB PDF)]

Motion is an important part of computer graphics. Skeletal motion, in particular, has been the focus of a great deal of research. Today, there exists a large body of techniques for processing and editing skeletal motion, increasing the versatility of each animation clip. However, analogous techniques have not yet been developed for deforming surface animations, where the surface geometry undergoes completely free-form motion. Likewise, polygonal meshes are a central part of computer graphics, and have also been the focus of much research. Many techniques have been developed for editing and approximating meshes with static geometry. However, these techniques do not generally carry over to deforming surfaces. This is unfortunate, as free-form deforming surfaces are becoming increasingly common in movies, games, and scientific applications. Moreover, these surfaces are frequently quite time-consuming to generate. It is therefore important to develop ways to increase the versatility of each generated motion clip. This dissertation presents the methods I have developed to do just that, allowing motion clips to be edited and processed in ways analogous to existing static mesh and skeletal motion methods. Also, deforming surfaces are frequently generated with entirely too many vertices for any given frame. This is especially true of physically generated animations (such as cloth), since the surface must be subdivided enough to accommodate any possible deformation. After generation, however, this extra detail is not needed for tasks such as rendering and playback. This dissertation presents my deforming surface approximation method, which yields a temporally coherent sequence of multiresolution meshes that approximate the surface at multiple levels of detail. I have also developed a simple but powerful rotation-invariant differential mesh representation that can easily accommodate any connected triangle mesh (including non-manifold and non-orientable surfaces). This representation is useful not only for free-form motion processing but also for general geometric mesh editing.

S. Kircher and M. Garland. Editing arbitrarily deforming surface animations. ACM Transactions on Graphics, Proceedings of SIGGRAPH 2006, July 2006. [Preprint (PDF)] [Movie (33MB WMV)] [Slides (118MB PPT)]

Deforming surfaces, such as cloth, can be generated through physical simulation, morphing, and even video capture. Up to this point, such data has been very dif ficult to alter after the generation process is complete. Data generated for one purpose cannot, for the most part, be adapted to other uses. Such adaption, however, would be extremely useful. Being able to take cloth captured from a flapping flag and attach it to a character to make a cape, or enhance the wrinkles on a simulated garment, would greatly enhance the usability and re-usability of deforming surface data. In addition, it is often necessary to cleanup or "tweak" simulation results. Doing this by editing each frame individually is a very time consuming and tedious process. Extensive research has investigated how to edit and re-use skeletal motion capture data, but very little has addressed completely non-rigid deforming surfaces. We have developed a novel method that now makes it easy to edit such arbitrary deforming surfaces. Our system enables global signal processing, direct manipulation, multiresolution embossing, and constraint editing on arbitrarily deforming surfaces, such as simulated cloth, motion-captured cloth, morphs, and other animations. The foundation of our method is a novel time-varying multiresolution transform, which adapts to the changing geometry of the surface in a temporally coherent manner.