View-independent Contour Culling of 3D Density Maps for Far-field Viewing of Iso-surfaces

In many applications, iso-surface is the primary method for visualizing the structure of 3D density maps. We consider a common scenario where the user views the iso-surfaces from a distance and varies the level associated with the iso-surface as well as the view direction to gain a sense of the general 3D structure of the density map. For many types of density data, the iso-surfaces associated with a particular threshold may be nested and never visible during this type of viewing. In this paper, we discuss a simple, conservative culling method that avoids the generation of interior portions of iso-surfaces at the contouring stage. Unlike existing methods that perform culling based on the current view direction, our culling is performed once for all views and requires no additional computation as the view changes. By pre-computing a single visibility map, culling is done at any iso-value with little overhead in contouring. We demonstrate the effectiveness of the algorithm on a range of bio-medical data and discuss a practical application in online visualization.     

A fast display method for volumetric data

Presented is a fast display method for volumetric data sets, which involves a slicebased method for extracting potentially visible voxels to represent visible surfaces. For a given viewing direction, the number of visible voxels can be trimmed further by culling most of the voxels not visible from that direction. The entire 3D array of voxels is also present for invasive operations and direct access to interior structures. This approach has been integrated on a low-cost graphic engine as an interactive system for craniofacial surgical planning that is currently in clinical use.     

一个根据几何信息对场景对象重组织以加速显示的方法

大规模场景图形应用和交互系统常常需要同时处理大量的场景对象。虽然场景结构对每帧的显示速度有很大的影响,但近几年来的研究和关注的重点已不是场景对象的组织结构,而主要集中在诸如物体表面的简化以及每个对象的表示等一致性特征上。场景中的物体几何信息的一致性十分易于理解,文中提出一个基于这些几何信息的分析方法以提升特定场景的显示效率。这个方法主要是将场景组织成层级结构。还提出了这个方法的许多变化形式,其中有些仅使用场景对象的几何信息,有些利用了场景固有的几何性质,而有些则同时使用了这些信息。最后还展示了一些统计信息,以证实文中的方法对图形交互应用效能的提升。     

Occlusion-Driven Scene Sorting for Efficient Culling

Image space occlusion culling is a powerful approach to reduce the rendering load of large polygonal models. However, occlusion culling is not for free; it trades overhead costs with the rendering costs of the possibly occluded geometry. Meanwhile, occlusion queries based on image space occlusion culling are supported on modern graphics hardware. However, a significant consumption of fillrate bandwidth and latency costs are associated with these queries. In this paper, we propose new techniques to reduce redundant occlusion queries. Our approach uses several "Occupancy Maps" to organize scene traversal. The respective information is accumulated efficiently by hardware‐supported asynchronous occlusion queries. To avoid redundant requests, we arrange these multiple occlusion queries according to the information of the Occupancy Maps. Our presented technique is conservative and benefits from a partial depth order of the geometry.     

Back-face culling applied to collision detection of polyhedra

Back-face culling is a preprocessing technique used in computer graphics to speed up the rendering of polyhedra. In this paper we show how this technique can be modified to reduce unnecessary checking of boundary elements in collison detection for a physical-based simulation and animation systems. At each time step, we determine a priori which faces cannot be part of the contact between two polyhedra and thus can be culled. In the computer graphics technique, the normal vector of a polygon is compared with the view direction. Here, the normal is compared to one or possibly several relative-velocity vectors, and the face is culled when its motion is in the opposite direction of the normal vector. We also give an algorithm that takes linear time in terms of the number of faces, and on the average eliminates half of the polygons. Owing to its low computational overhead, when it is used as a front end to a collision detection system, a noticeable improvement in performance can be achieved.     

Efficient convex hull computation for planar freeform curves

We present an efficient real-time algorithm for computing the precise convex hulls of planar freeform curves. For this purpose, the planar curves are initially approximated with G¹-biarcs within a given error bound ε in a preprocessing step. The algorithm is based on an efficient construction of approximate convex hulls using circular arcs. The majority of redundant curve segments can be eliminated using simple geometric tests on circular arcs. In several experimental results, we demonstrate the effectiveness of the proposed approach, which shows the performance improvement in the range of 200-300 times speed up compared with the previous results (Elber et al., 2001) [8].