Catálogo de publicaciones - libros

Transfer function is very important for volume rendering. One common approach is to map the gradient magnitude to opacity transfer functions. However, it catches too many small details. Gradient vector flow (GVF) vectors have large magnitudes in the immediate vicinity of the edges, where the GVF vectors keep coordinate with the vectors of the gradient of the edge map. While in homogeneous regions where the intensity is nearly constant, the magnitudes of gradient vectors are nearly zero and GVF diffuses the edge gradient. Because of these aspects, we extend GVF to color space and apply it for opacity transfer functions. Experiments show that our method enhances edge features and makes a visual effect of diffusing along the edges.

This paper presents a quasi-physically based approach for interactively simulating large-scale dynamic forest scenes under different wind conditions. We introduce theories from the wind engineering , and model the natural wind field as a stationary stochastic process. To reduce the geometry complexities without sacrificing much image quality, we adopt a hybrid geometry/image representation scheme to faithfully model the appearance of trees. Some simplified mechanical rules are employed to compute the movement of such tree models. Three kinds of level of details concerning the scene geometry, the movement of trees and the wind field, are exploited to accelerate the simulation. For forest scenes with tens of thousands of animated trees, our implementation with programable graphics hardware achieves visually plausible results at interactive frame rates on consumer PC platforms.

This paper addresses some properties of G ^1 continuity conditions between two B-spline surfaces with arbitrary degrees and generally structured knots. Key issues addressed in the paper include necessary G ^1 continuity conditions between two B-spline surfaces, general connecting functions, continuities of the general connecting functions, and intrinsic conditions of the general connecting functions along the common boundary. In general, one may use piecewise polynomial functions, i.e. B-spline functions, as connecting functions for G ^1 connection of two B-spline surfaces. Based on the work reported in this paper, some recent results in literature using linear connecting functions are special cases of the general connecting functions reported in this paper. In case that the connecting functions are global linear functions along the common boundary commonly used in literature, the common boundary degenerates as a Bézier curve for proper G ^1 connection. Several examples for connecting two uniform biquadratic B-spline surfaces with G ^1 continuity are also presented to demonstrate the results.

Face represents complex, multi dimensional, meaningful visual stimuli. Computational models for face recognition represent the problem as a high dimensional pattern recognition problem. This paper introduces an innovative facial identification method using eigenface approach on volume-based graphics rather than 2D photo-images. We propose to convert polygon mesh surface to a volumetric representation by regular sampling in a volumetric space. Our motivation is to extend existing 2D facial analysis techniques to a 3D image space by taking advantage of use of the volumetric representation. We apply principle component analysis (PCA) for dimensionality reduction. Face feature patterns are projected onto a lower dimensional PCA sub-space that spans the known facial patterns. 3D eigenface feature space is constructed for face identification.

This paper presents an algorithm for interpolating curves with predefined cross curvature on subdivision surfaces using polygonal complexes. The cross curvature is defined by a separate 2-D polygon which can be used to generate a complex along the control path. A straightforward application is the generation of Catmull-Clark subdivision surfaces that flow nicely along feature curves. Interactive manipulation of the 2-D polygon will correspond to a variety of features along the interpolated curves such as ribs, bumps, cavities, or even sharp creases.