Tensor Topology Tracking: A Visualization Method for Time-Dependent 2D Symmetric Tensor Fields

Topological methods produce simple and meaningful depictions of symmetric, second order two-dimensional tensor fields. Extending previous work dealing with vector fields, we propose here a scheme for the visualization of time-dependent tensor fields. Basic notions of unsteady tensor topology are discussed. Topological changes - known as bifurcations - are precisely detected and identified by our method which permits an accurate tracking of degenerate points and related structures.     

Spatial Patches - A Primitive for 3D Model Representation

The commonly used solution for real-life 3D model representation is polygonal spatially consistent geometry, with texture, and, optionally, bump or displacement maps attached. Although the idea of displacement mapping is well known, there are just a few approaches to its efficient implementation. In this paper we develop a technique that allows for efficient representation and rendering of 3D models by getting a new angle on the displacement mapping concept. We introduce a new primitive that is defined as the range image of a small part of the model's surface; therefore, it is called a spatial patch. The whole model is just a collection of patches with no connectivity information between them. Such a representation can be directly acquired by 3D scanning machinery, and stored in a compact uniform form. It also allows for efficient visualization, which is the major focus of this paper. Thus, we present the logical structure of a rendering unit based on conventional z-buffering, and discuss the involved algorithms in detail. These algorithms benefit from modern features of computing units for which we believe the proposed technique can be used in a wide range of applications dealing with real-life 3D data.     

Valence-Driven Connectivity Encoding for 3D Meshes

In this paper, we propose a valence-driven, single-resolution encoding technique for lossless compression of triangle mesh connectivity. Building upon a valence-based approach pioneered by Touma and Gotsman²² , we design a new valence-driven conquest for arbitrary meshes that always guarantees smaller compression rates than the original method. Furthermore, we provide a novel theoretical entropy study of our technique, hinting the optimality of the valence-driven approach. Finally, we demonstrate the practical efficiency of this approach (in agreement with the theoretical prediction) on a series of test meshes, resulting in the lowest compression ratios published so far, for both irregular and regular meshes, small or large.     

Linear Interval Estimations for Parametric Objects Theory and Application

The new concept of parametrized bounding volumes for parametric objects is proposed to replace the common compact bounding volumes like axis aligned bounding boxes and parallelepipeds. Linear Interval Estimations (LIEs) are developed as a realization of the discussed ideas. Two reliable methods for the computation of LIEs are introduced based on a new understanding of the use of affine arithmetics and a special application of Taylor Models. The particular structure of LIEs allows an effective intersection test of LIEs with rays, boxes and other LIEs. The test gives besides of a possible location of the intersection in object space information about affected parts in the parameter spaces of the enclosed objects. A subdivision algorithm for the intersection of two parametric surface patches with remarkable experimental results is presented as a possible application.     

Coarse-to-fine surface simplification with geometric guarantees

Let PC be a 3D point cloud and ε be a positive value called tolerance. We aim at constructing a triangulated surface S based on a subset PCU of PC such that all the points in PCL = PC ∖ PCU are at distance at most ε from a facet of S . (PCU and PCL respectively stand for Point Cloud Used and Point Cloud Left .) We call this problem simplification with geometric guarantees.
This paper presents a new framework to simplify with geometric guarantees. The approach relies on two main ingredients. First an oracle providing information on the surface being reconstructed even though the triangulated surface itself has not been computed. Second, a reconstruction algorithm providing incremental updates of the reconstructed surface, as well as a fast point-to-triangles distance computation. The oracle is used to guess a subset of the point cloud from which a triangulated surface is reconstructed. It relies on an implicit surface the triangulated surface is an approximation of, and is therefore available before the triangle mesh. The point-to-triangles distance computation and the local updates are then invoked to insert new vertices until the tolerance is met.
We also present a detailed experimental study which shows the efficiency of the simplification process both in terms of simplification rate and running time.
To the best of our knowledge, this algorithm is the first one performing coarse-to-fine surface simplification with geometric guarantees.     

Fast Visualization of Object Contours by Non-Photorealistic Volume Rendering

In this paper we present a fast visualization technique for volumetric data, which is based on a recent non-photorealistic rendering technique. Our new approach enables alternative insights into 3D data sets (compared to traditional approaches such as direct volume rendering or iso-surface rendering). Object contours, which usually are characterized by locally high gradient values, are visualized regardless of their density values. Cumbersome tuning of transfer functions, as usually needed for setting up DVR views is avoided. Instead, a small number of parameters is available to adjust the non-photorealistic display. Based on the magnitude of local gradient information as well as on the angle between viewing direction and gradient vector, data values are mapped to visual properties (color, opacity), which then are combined to form the rendered image (MIP is proposed as the default compositing stragtegy here). Due to the fast implementation of this alternative rendering approach, it is possible to interactively investigate the 3D data, and quickly learn about internal structures. Several further extensions of our new approach, such as level lines are also presented in this paper.     

Accurate and Fast Proximity Queries Between Polyhedra Using Convex Surface Decomposition

The need to perform fast and accurate proximity queries arises frequently in physically-based modeling, simulation, animation, real-time interaction within a virtual environment, and game dynamics. The set of proximity queries include intersection detection, tolerance verification, exact and approximate minimum distance computation, and (disjoint) contact determination. Specialized data structures and algorithms have often been designed to perform each type of query separately. We present a unified approach to perform any of these queries seamlessly for general, rigid polyhedral objects with boundary representations which are orientable 2-manifolds. The proposed method involves a hierarchical data structure built upon a surface decomposition of the models. Furthermore, the incremental query algorithm takes advantage of coherence between successive frames. It has been applied to complex benchmarks and compares very favorably with earlier algorithms and systems.     

体绘制中显示隐含分界面的一种方法及其实现

在普通的体光照模型下,使用直接体绘制显示对象内部的隐含分界面(内部不同介质之间的分界面),需要改变传递函数,确定体素的颜色值和不透明度.虽然能够看到对象内部的结构,但是在这种模型下,要透过物体的表面清晰地看到其内部的隐含分界面是不可能的.这一方面是由于普通体光照模型中的粒子不具有选择透光性,即不能透过波长在一定范围内的可见光而吸收另一部分波长不同的可见光,只能同等地吸收各种波长的光;另一方面是因为普通体光照模型缺乏表面信息部分.该算法使用一种具有选择透光性的体光照模型,在这种模型中加入表面散射部分,这一部分与视线、光源位置无关,同时采用非真实感绘制技术来加大隐含分界面的显示效果.在这种光照模型下,可以清晰地显示出隐含分界面具体的细节部分.     

一种草图形式的视频摘要生成方法

视频摘要作为一种视频内容的简要表示,能够有效地增强用户浏览和组织视频的效率。提出了一种基于草图的视频摘要生成方法。与以往的静态视频摘要方法不同,该方法结合视频内容分析,利用草图在表达上的简洁性和抽象性,对视频中的主要内容进行表达。首先通过视频分析获取视频中的语义特征并提取关键帧,然后通过交互式的方法从关键帧中生成草图,最后进行摘要布局生成完整的视频摘要。实验结果表明,该方法能够有效突出视频的主要对象和主要事件,并具有较高的用户满意度。     

Real-Time Watercolor for Animation

We present algorithms that allow for real-time rendering of 3D-scenes with a watercolor painting appearance. Our approach provides an appropriate simplification of the visual complexity, imitates characteristic natural effects of watercolor, and provides two essential painting techniques: the wet-on-wet and the wet-on-dry painting. We concentrate on efficient algorithms based on image space processing rather than on an exact simulation. This allows for the real-time rendering of 3D-scenes. During an animation a high frame-to-frame coherence can be achieved due to a stable segmentation scheme. Finally, we seamlessly integrate a smooth illumination into the watercolor renderings using information from the 3D-scene.