Over the past several years, I've worked on a variety of research topics including 3D texture synthesis, stereology, rapid visualization of large terrain datasets, realtime deformable models, procedural modeling, and haptic interfaces. I completed my Ph.D. at MIT in the Computer Graphics Group within the Computer Science & Artificial Intelligence Laboratory (CSAIL). Listed below are the abstracts from select publications. Please also visit my personal homepage. |

Stereological Techniques for Synthesizing Solid Textures from Images of Aggregate MaterialsRobert JagnowDoctoral Thesis, MIT.pdf (42Mb) When creating photorealistic digital scenes, textures are commonly used to depict complex variation in surface appearance. For materials that have spatial variation in three dimensions, such as wood or marble, solid textures offer a natural representation. Unlike 2D textures, which can be easily captured with a photograph, it can be difficult to obtain a 3D material volume. This thesis addresses the challenge of extrapolating tileable 3D solid textures from images of aggregate materials, such as concrete, asphalt, terrazzo or granite. |

Stereological Techniques for Solid TexturesRobert Jagnow, Julie Dorsey, and Holly RushmeierProceedings of SIGGRAPH 2004.pdf (16.5Mb) Powerpoint XP Slides (4.8Mb) .pdf Slides (0.7Mb) We describe the use of traditional stereological methods to synthesize 3D solid textures from 2D images of existing materials. We first illustrate our approach for aggregate materials of spherical particles, and then extend the technique to apply to particles of arbitrary shapes. We demonstrate the effectiveness of the approach with side-by-side comparisons of a real material and a synthetic model with its appearance parameters derived from its physical counterpart. Unlike ad hoc methods for texture synthesis, stereology provides a disciplined, systematic basis for predicting material structure with well-defined assumptions. |

Virtual Sculpting with Haptic Displacement MapsRobert Jagnow and Julie DorseyProceedings of Graphics Interface, May 2002..pdf (15Mb) Movie (2 minutes, 10 Mb, MPEG 1) This paper presents an efficient data structure that facilitates high-speed haptic (force feedback) interaction with detailed digital models. Models are partitioned into coarse slabs, which collectively define a piecewise continuous vector field over a thick volumetric region surrounding the surface of the model. Within each slab, the surface is represented as a displacement map, which uses the vector field to define a relationship between points in space and corresponding points on the model's surface. This representation facilitates efficient haptic interaction without compromising the visual complexity of the scene. Furthermore, the data structure provides a basis for interactive local editing of a model's color and geometry using the haptic interface. We describe implementation details and demonstrate the use of the data structure with a variety of digital models. |

A Procedural Approach to Authoring Solid ModelsBarbara Cutler, Julie Dorsey, Leonard McMillan, Matthias Mueller, and Robert JagnowProceedings of ACM SIGGRAPH 2002.pdf (11.3Mb) Project Homepage We present a procedural approach to authoring layered, solid models. Using a simple scripting language, we define the internal structure of a volume from one or more input meshes. Sculpting and simulation operators are applied within the context of the language to shape and modify the model. Our framework treats simulation as a modeling operator rather than simply as a tool for animation, thereby suggesting a new paradigm for modeling as well as a new level of abstraction for interacting with simulation environments. Capturing real-world effects with standard modeling techniques is extremely challenging. Our key contribution is a concise procedural approach for seamlessly building and modifying complex solid geometry. We present an implementation of our language using a flexible tetrahedral representation. We show a variety of complex objects modeled in our system using tools that interface with finite element method and particle system simulations. |

Stable Real-Time DeformationsMatthias Müller, Julie Dorsey, Leonard McMillan, Robert Jagnow, and Barbara CutlerProceedings of ACM SIGGRAPH Symposium on Computer Animation 2002.pdf (1.3Mb) Live Java Demo The linear strain measures that are commonly used in real-time animations of deformable objects yield fast and stable simulations. However, they are not suitable for large deformations. Recently, more realistic results have been achieved in computer graphics by using Green's non-linear strain tensor, but the non-linearity makes the simulation more costly and introduces numerical problems. In this paper, we present a new simulation technique that is stable and fast like linear models, but without the disturbing artifacts that occur with large deformations. As a precomputation step, a linear stiffness matrix is computed for the system. At every time step of the simulation, we compute a tensor field that describes the local rotations of all the vertices in the mesh. This field allows us to compute the elastic forces in a non-rotated reference frame while using the precomputed stiffness matrix. The method can be applied to both finite element models and mass-spring systems. Our approach provides robustness, speed, and a realistic appearance in the simulation of large deformations. |

Real-Time Simulation of Deformation and Fracture of Stiff MaterialsMatthias Müller, Leonard McMillan, Julie Dorsey, and Robert JagnowProceedings of EUROGRAPHICS 2001.pdf (1Mb) Existing techniques for real-time simulation of object deformation are well suited for animating soft materials like human tissue or two-dimensional systems such as cloth. However, simulation of deformation in malleable materials and fracture in brittle materials has only been done offline because the underlying equations of motion are numerically stiff, requiring many small steps in explicit integration schemes. In contrast, the better-behaved implicit integration techniques are computationally expensive, particularly for volumetric meshes. We present a stable hybrid method for simulating deformation and fracture of materials in real-time. In our system, the effects of impact forces are computed only at discrete collision events. At these impacts, we treat objects as if they are anchored and compute their static equilibrium response using the Finite Element technique. Static analysis is not time-step bound and its stability is independent of the stiffness of the equations. The resulting deformations, or possible fractures, are computed based on internal stress tensors. Between collisions, disconnected objects are treated as rigid bodies. The simulator is demonstrated as part of a system that provides the user with physically-based tools to interactively manipulate 3D models. |

Last Modified February 13, 2006