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.     

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.     

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.     

视觉感知的图像和视频抽象

可靠的视觉感知估计体现的是对图像中有意义的那部分结构信息的理解。基于此,描述一个完整的图像和视频抽象化框架,通过一种边缘保持的滤波器有区分地风格化抽象图像和视频的显著部分和非显著部分,并保持两部分之间的和谐过渡。首先,对于显著区域的识别引入一种自动显著性目标分割算法,基于局部空间邻域的自动显著性计算。考虑到实际需要,提供了交互式技术,方便有目的地去指定图像中的显著结构信息。然后,根据生成的显著结构信息掩模使用单尺度的各向异性滤波处理显著部分,而用多尺度的同种滤波处理非显著部分以实现更强程度的抽象效果。本文方法生成的图像和视频的抽象化不仅呈现了视觉满意的非真实感效果,而且在软量化后还可以应用于其他风格的非真实感渲染(NPR)效果的实现。实验结果显示,处理一定数量的图像及视频,本文方法可以得到期望的结果。     

Rendering Silhouettes with Virtual Lights

We present a new method for obtaining non-photorealistic images. These images have two main visual components: silhouettes and non-realistic colouring. Silhouettes are lines that define the form of an object. They are used in classical animation and illustration as the main expressive components. In these applications, if it is necessary, colouring can be added once the drawings are made. For instance, generally, in illustration, colouring is flat and does not transmit volume information whilst silhouettes do it in an economical way. The proposed method is based on the Virtual Lights model, which allows us to use external components, the virtual lights, to define silhouettes. In this way, the designer is free to control where, when and how the silhouettes must appear. The method can be used with B-rep geometric models.     

加速体绘制技术

根据体绘制成像的各个操作环节,对体绘制的加速技术进行了较全面且系统的介绍,包括色彩合成、光线与数据的求交、插值计算、排序及视见变换、对体绘制的基于硬件及系统方面的加速技术（如并行体绘制和漫游体绘制）也进行了一些讨论,在实际应用中,只有将各种加速技术进行有机地结合才能充分发挥体绘制的可视化作用。