David E. Breen

Predicting the drape of woven cloth using interacting particles

We demonstrate a physically-based technique for predicting the drape of a wide variety of woven fabrics. The approach exploits a theoretical model that explicitly represents the microstructure of woven cloth with interacting particles, rather than utilizing a continuum approximation. By testing a cloth sample in a Kawabata fabric testing device, we obtain data that is used to tune the models energy functions, so that it reproduces the draping behavior of the original material. Photographs, comparing the drape of actual cloth with visualizations of simulation results, show that we are able to reliably model the unique large-scale draping characteristics of distinctly different fabric types.

Level set surface editing operators

We present a level set framework for implementing editing operators for surfaces. Level set models are deformable implicit surfaces where the deformation of the surface is controlled by a speed function in the level set partial differential equation. In this paper we define a collection of speed functions that produce a set of surface editing operators. The speed functions describe the velocity at each point on the evolving surface in the direction of the surface normal. All of the information needed to deform a surface is encapsulated in the speed function, providing a simple, unified computational framework. The user combines pre-defined building blocks to create the desired speed function. The surface editing operators are quickly computed and may be applied both regionally and globally. The level set framework offers several advantages. 1) By construction, self-intersection cannot occur, which guarantees the generation of physically-realizable, simple, closed surfaces. 2) Level set models easily change topological genus, and 3) are free of the edge connectivity and mesh quality problems associated with mesh models. We present five examples of surface editing operators: blending, smoothing, sharpening, openings/closings and embossing. We demonstrate their effectiveness on several scanned objects and scan-converted models.

Cloth modeling and animation

Written by leaders in the field of computer clothing design and simulation, Cloth Modeling and Animation is a vital resource for researchers and developers of cloth simulation software as well as computer animators and graphics programmers. Readers will learn about cloths nature and structure, scientific approaches to understanding its behavior and look, and the latest modeling and simulation techniques for automatically animating cloth on the computer.

Calibration requirements and procedures for a monitor-based augmented reality system

Augmented reality entails the use of models and their associated renderings to supplement information in a real scene. In order for this information to be relevant or meaningful, the models must be positioned and displayed in such a way that they blend into the real world in terms of alignments, perspectives, illuminations, etc. For practical reasons the information necessary to obtain this realistic blending cannot be known a priori, and cannot be hard wired into a system. Instead a number of calibration procedures are necessary so that the location and parameters of each of the system components are known. We identify the calibration steps necessary to build a computer model of the real world and then, using the monitor based augmented reality system developed at ECRC (GRASP) as an example, we describe each of the calibration processes. These processes determine the internal parameters of our imaging devices (scan converter, frame grabber, and video camera), as well as the geometric transformations that relate all of the physical objects of the system to a known world coordinate system. >

A particle-based model for simulating the draping behavior of woven cloth

We demonstrate a physically based technique for producing draping simulations of a variety of woven fabrics. Our approach employs an interacting-particle model based on the microstructure of woven cloth, rather than using a continuum approx imation. Empirical data from a fabric testing device are used to tune energy functions within the model. We describe the model, how we convert the fabric test data to energy functions, and two experiments we conducted to evaluate the approach. The first experiment produces nonlinear mechanical data from the model. The second exper iment compares photographs of three different kinds of draping cloth with visualizations of simulation results. The experiments show that we are able to reliably recover quan titative mechanical information from the model and to reproduce the unique large- scale draping characteristics of a range of fabrics.

Real-time vision-based camera tracking for augmented reality applications

Augmentedreality deals with the problem of dynamically augmenting or enhancing (images or live video of) the real world with computer generated data (e.g., graphics of virtual objects). This poses two major problems: (a) determining the precise alignment of real and virtual coordinate frames for overlay, and (b) capturingthe 3D environmentincluding camera and object motions. The latter is important for interactive augmented reality applications where users can interact with both real and virtual objects. Here we address the problem of accurately tracking the 3D motion of a monocular camera in a known 3D environment and dynamically estimating the 3D camera location. We utilize fully automated landmark-basedcamera calibration to initialize the motion estimation and employ extended Kalman filter techniques to track landmarksand to estimate the camera location. The implementation of our approach has been proven to be efficient and robust and our system successfully tracks in real-time at approximately 10 Hz.

Semi-regular mesh extraction from volumes

We present a novel method to extract iso-surfaces from distance volumes. It generates high quality semi-regular multiresolution meshes of arbitrary topology. Our technique proceeds in two stages. First, a very coarse mesh with guaranteed topology is extracted. Subsequently an iterative multi-scale force-based solver refines the initial mesh into a semi-regular mesh with geometrically adaptive sampling rate and good aspect ratio triangles. The coarse mesh extraction is performed using a new approach we call surface wavefront propagation. A set of discrete iso-distance ribbons are rapidly built and connected while respecting the topology of the iso-surface implied by the data. Subsequent multi-scale refinement is driven by a simple force-based solver designed to combine good iso-surface fit and high quality sampling through reparameterization. In contrast to the Marching Cubes technique our output meshes adapt gracefully to the iso-surface geometry, have a natural multiresolution structure and good aspect ratio triangles, as demonstrated with a number of examples.

3D scan conversion of CSG models into distance volumes

A distance volume is a volume dataset where the value stored at each voxel is the shortest distance to the surface of the object being represented by the volume. Distance volumes are a useful representation in a number of computer graphics applications. We present a technique for generating a distance volume with sub-voxel accuracy from one type of geometric model, a constructive solid geometry (CSG) model consisting of superellipsoid primitives. The distance volume is generated in a two step process. The first step calculates the shortest distance to the CSG model at a set of points within a narrow band around the evaluated surface. Additionally, a second set of points, labeled the zero set, which lies on the CSG models surface are computed. A point in the zero set is associated with each point in the narrow band. Once the narrow band and zero set are calculated, a fast marching method is employed to propagate the shortest distance and closest point information out to the remaining voxels in the volume. Our technique has been used to scan convert a number of CSG models, producing distance volumes which have been utilized in a variety of computer graphics applications, e.g. CSG surface evaluation, offset surface generation, and 3D model morphing.

Interactive occlusion and automatic object placement for augmented reality

We present several techniques for producing two visual and modeling effects in augmented reality. The first effect involves interactively calculating the occlusions between real and virtual objects. The second effect utilizes a collision detection algorithm to automatically move dynamic virtual objects until they come in contact with static real objects in augmented reality. All of the techniques utilize calibrated data derived from images of a real‐world environment.

A physically-based particle model of woven cloth

Every time a tablecloth is draped over a table it will fold and pleat in unique ways. We report on a physically-based model and a simulation methodology, which when used together are able to reproduce many of the attributes of this characteristic behavior of cloth. Our model utilizes a microscopic particle representation that directly treats the mechanical constraints between the threads in woven material rather than using a macroscopic continuum approximation. The simulation technique is hybrid, employing force methods for gross movement and energy methods to enforce constraints within the material. The model is developed and demonstrated within a visualization environment that allows full interaction between the simulated material and conventional constructive-solid-geometry models.