树型结构预处理算法及在游戏引擎中的实现

经过分析和验证，以八叉树碰撞节点生成为例，采用文件一次性记录划分结果，并在渲染时从文件读取，有效的缩短了生成八叉树的时间。此项设计也是游戏引擎中的一个功能模块。     

大规模战场电磁环境并行体绘制技术研究

提出了一种基于PC集群的大规模三维战场电磁环境并行绘制方法。该方法采用直接体绘制的三维体数据可视化方法;利用空间八叉树对电磁绘制区间进行空间分割,并采用先序遍历八叉树叶节点的方式进行任务分配;采用Binary-swap算法对各PC节点的生成图像逐次进行全屏幕深度合成。实验表明,该方法能够较好满足大规模战场电磁环境实时可视化的要求。     

基于颜色对的色彩量化算法

提出了一种新颖的基于颜色对的色彩量化算法。综合考虑了色彩层次感和关键细节的要求,并且可以根据具体色彩量化任务的要求,对它们的偏重性做出调整,以得到最满意的量化结果。     

Discrete Ray-Tracing of Huge Voxel Spaces

The quality of images produced by Discrete Ray-Tracing voxel spaces is highly dependent on 3d grid resolution. The huge amount of memory needed to store such grids often discards discrete Ray-Tracing as a practical visualization algorithm. The use of an octree can drastically change this when most of space is empty, as such is the case in most scenes. Although the memory problem can be bypassed using the octree, the performance problem still remains. A known fact is that the performance of discrete traversal is optimal for quite low resolutions. This problem can be easily solved by dividing the task in two steps, working in two low resolutions instead of just one high resolution, thus taking advantage of optimal times in both steps. This is possible thanks to the octree property of representing the same scene in several different resolutions. This article presents a two step Discrete Ray-Tracing method using an octree and shows, by comparing it with the single step version, that a substantial gain in performance is achieved.     

基于PCL的点云数据压缩研究

研究基于开源C++编程库PCL(点云库),在VS2010平台上读取由Kinect获取的PLY格式的三维模型数据,利用PCL的Octree(八叉树)类为点云数据构建八叉树结构、进行八叉树编码,实现了点云数据的高效压缩方案。此压缩方案可以针对不同的应用场合设置不同的精简点距离,简洁高效,减少了数据的空间占用,且便于数据的在线传输。     

Algorithms for the physical rendering and assembly of octree models

Hierarchical decomposition techniques are well established for the representation of 2D images, the calculation of distance maps, and the modelling of volume data. However, recent work has suggested that their use can be extended to the manufacture of physical objects for low cost prototyping and visualization. This paper details various decomposition and assembly planning routines created to support this process. Specifically the decomposition methods are described to generate octants appropriate for the physical assembly process. Having established methods for generating suitable octrees, three different algorithms for planning the assembly of octrees are presented. The comparative performance of these different approaches is discussed.     

Fast Volume Rendering and Data Classification Using Multiresolution in Min‐Max Octrees

Large‐sized volume datasets have recently become commonplace and users are now demanding that volume‐rendering techniques to visualise such data provide acceptable results on relatively modest computing platforms. The widespread use of the Internet for the transmission and/or rendering of volume data is also exerting increasing demands on software providers. Multiresolution can address these issues in an elegant way. One of the fastest volume‐rendering alrogithms is that proposed by Lacroute & Levoy ¹ , which is based on shear‐warp factorisation and min‐max octrees (MMOs). Unfortunately, since an MMO captures only a single resolution of a volume dataset, this method is unsuitable for rendering datasets in a multiresolution form. This paper adapts the above algorithm to multiresolution volume rendering to enable near‐real‐time interaction to take place on a standard PC. It also permits the user to modify classification functions and/or resolution during rendering with no significant loss of rendering speed. A newly‐developed data structure based on the MMO is employed, the multiresolution min‐max octree, M ³ O, which captures the spatial coherence for datasets at all resolutions. Speed is enhanced by the use of multiresolution opacity transfer functions for rapidly determining and discarding transparent dataset regions. Some experimental results on sample volume datasets are presented.     

From A Medial Surface To A Mesh

Medial surfaces are well‐known and interesting surface skeletons. As such, they can describe the topology and the geometry of a 3D closed object. The link between an object and its medial surface is also intuitively understood by people. We want to exploit such skeletons to use them in applications like shape creation and shape deformation. For this purpose, we need to define medial surfaces as Shape Representation Models (SRMs). One of the very first task of a SRM is to offer a visualization of the shape it describes. However, achieving this with a medial surface remains a challenging problem. In this paper, we propose a method to build a mesh that approximates an object only described by a medial surface. To do so, we use a volumetric approach based on the construction of an octree. Then, we mesh the boundary of that octree to get a coarse approximation of the object. Finally, we refine this mesh using an original migration algorithm. Quantitative and qualitative studies, on objects coming from digital modeling and laser scans, shows the efficiency of our method in providing high quality surfaces with a reasonable computational complexity.     

An adjustable algorithm for color quantization

Color quantization is an important technique in digital image processing. Generally it involves two steps. The first step is to choose a proper color palette. The second step is to reconstruct an image by replacing original colors with the most similar palette colors. However a problem exists while choosing palette colors. That is how to choose the colors with different illumination intensities (we call them color layers) as well as the colors that present the essential details of the image. This is an important and difficult problem. In this paper, we propose a novel algorithm for color quantization, which considers both color layers and essential details by assigning weights for pixel numbers and color distances. Also this algorithm can tune the quantization results by choosing proper weights. The experiments show that our algorithm is effective for adjusting quantization results and it also has very good quality of quantization.     

Oriented bounding box and octree based global interference detection in 5-axis machining of free-form surfaces

Global interference detection is a critical problem in 5-axis NC machining of free-form surfaces. Based on the hierarchical oriented bounding box (OBB) which is used in virtual reality to detect spatial collisions between 3D objects, a new global interference detection method is developed in this paper. In this method, in order to simplify the computation process of updating tool positions and orientations in 5-axis machining, the cutter and cutter holder are modeled by a hierarchical OBB structure, whereas the workpiece surfaces are approximated by an octree. Interference detection is conducted between the tool OBBs and the gray octants of the surface octree with the separating axis theorem. With the hierarchical structure of octree, if interference is found in one octant, its sub-octants are further processed to locate the exact colliding leaf nodes and the discretized surface points contained in these leaf nodes are tested with a conventional vector calculation method for exact interference detection; if no interference is detected, all the sub-octants are then considered as interference free and are not processed further. Meanwhile, with the hierarchical structure of the tool OBBs, should interference occur between octants and the OBBs in the first level of the hierarchical structure, the sub-OBBs in the second level would be further tested. Otherwise it could be determined with certainty that there is no interference between the tool and the octant.