基于3D扫描技术的数控雕刻系统

本文介绍了一种基于3D扫描技术来实现先进高速雕刻的数控雕刻系统.即利用物体表面三维形状测量技术来获取实物模型表面的3D扫描数据,经计算机处理之后,存储为3D格式文件,再将该格式的文件转换成刀路NC格式文件,最后输入到数控雕刻系统的输入单元内雕刻出物体的3D模型.整个系统的软硬件自行设计搭建,并在文中给出了实例制作过程.     

一种鲁棒性的2D矢量图形水印算法

为了解决空间信息网络传输和空间信息共享的版权保护问题,提出了一种具有鲁棒性的2D矢量图形的水印算法。在GIS中,矢量图形是其最基本的表达方式,常需针对2D矢量图形的大数据集进行水印嵌入处理,本方法先将空间矢量图层按照自身所含的多边形特征进行分解;对分解后的矢量多边形进行分析,选择合适的多边形的线段,在其顶点处嵌入水印;而提取水印的过程,则是对原矢量图形和水印图形进行分析,根据嵌入水印顶点的位置或坐标值得到水印信息的序列。实验结果证明,该方法对于空间信息的常规图形操作,如矢量图层的坐标变换、平移、旋转、缩放,以及图形的剪切,点的添加删除等,均具有较强的鲁棒性。     

A Direct Manipulation Technique for Specifying 3D Object Transformations with a 2D Input Device

A mechanism is presented for direct manipulation of 3D objects with a conventional 2D input device, such as a mouse. The user can define and modify a model by graphical interaction on a 3D perspective or parallel projection. A gestural interface technique enables the specification of 3D transformations (translation, rotation and scaling) by 2D pick and drag operations. Interaction is not restricted to single objects but can be applied to compound objects as well. The method described in this paper is an easy-to-understand 3D input technique which does not require any special hardware and is compatible with the designer's mental model of object manipulation.     

A framework for GPU-based application-independent 3D interactions

Direct manipulation using pointing devices commonly relies on basic interaction tasks such as selection and precise cursor positioning. Traditionally, such tasks use geometric attributes computed on the basis of application-dependent intersection algorithms on the CPU. However, with the recent ability of using GPUs to perform geometry modeling tasks and even to create new primitives on-the-fly, geometric attributes computed on the CPU are often invalid. We analyze a new paradigm for correctly computing such attributes based on providing, for each pixel of the rendered models, application-defined data and elements of discrete differential geometry computed solely on the GPU. We validate this by showing how many direct manipulation tasks presented in the literature require only these data, and present an interaction framework that exploits such paradigm. Implementation results are presented.

Architectures of Graphic Processors for Interactive 2D Graphics

Interactive 2-D systems have benefited greatly from the improvements in 1C technology. Today, the trend is to relieve the host computer from low level tasks through increasing the graphic system's computational power. The introduction of video RAMs has solved the problem of contention for memory cycles between the display generator and the video refresh controller. The improvements in graphic controllers have led from the first fixed instructions controllers to today's third generation of programmable graphic processors, able to support computer graphic interface standards. This article will present this evolution, and focus on a 2-D graphic processor designed at the Imagery, Instrumentation and Systems Laboratory, based on the separation of graphic generation and memory management functions.     

三维模型的二维矢量化机制的研究与实现

论述了三维模型二维图形矢量化的必要性,详细描述了一种三维模型的二维矢量化机制,包括三维模型的一致化建模方式以及模型的组织与分层聚合方法,并对以往的隐藏几何元素消除算法做出改进,使其适应三维空间曲面的情况。     

Line-based sunken relief generation from a 3D mesh

Sunken relief is an art form made by cutting the relief sculpture itself into a flat surface with a shallow overall depth. This paper focuses on the problem of direct generation of line-based sunken relief from a 3D mesh. We show how to extract, post-process and organize the messy feature lines in regular forms, applicable for lines engraving on the sculpture surfaces. We further describe how to construct a smooth height field from the input object, and derive a continuous pitting corrosion method to generate the cutting paths. The whole framework is conducted in object-space, making it flexible for stroke stylization and depth control of the engraving lines. We demonstrate the results with several impressive renderings and photographs used to illustrate the paper itself.     

一种二维矢量图形的硬件优化渲染算法

提出了一种适用于嵌入式设备的二维矢量图形硬件优化渲染算法。在采用超采样反锯齿模式下,该算法中每个像素点只使用一个方向权重计数器,而并非以往算法中每个像素点使用多个计数器,从而达到节省硬件资源,并大幅减少渲染所需计算量的效果。实验结果表明,和以往算法相比,在8-queen超采样模式和XVGA显示大小下,能节省83%的存储器使用量和65%的存储器访问量,并且能取得较好的反锯齿效果。     

二维和三维矢量场的可视化

矢量场可视化用来帮助人们直观理解二维和三维矢量场。由于目前的矢量场可视化方法只能展示二维矢量场的方向而不能展示强度,并且对于三维矢量场可视化的效果不太令人满意,因此本文提出了用线积分卷积来实现二维平面矢量场可视化,以及三维空间矢量场可视化的方法。对于线积分卷积中的流线跟踪,利用扩展的Bresenham画线算法的思想,实现了二维平面和三维空间流线的跟踪,并且通过建立一个二维表和三维表来分别存储二维平面矢量场和三维空间矢量场中每个点在流线中的上一个点和下一点的位置,来避免传统流线跟踪方法的冗余计算,提高了效率。对于二维平面矢量场,把线积分卷积的结果和矢量的强度进行加权平均,从而利用输出图像的纹理和颜色,共同来表现矢量场的方向和强度。对于三维空间矢量场,利用体线积分卷积（Volume Line Integral Convolution, Volume LIC）的方法来得到输出体纹理,并且用光线投射的体渲染方法来展示三维空间矢量场。结果显示出本文的方法能够清晰直观的看到二维平面矢量场和三维空间矢量场。     

Visualization techniques for 3D vector fields: an application to electrostatic fields of molecules

In chemistry, computer graphics is now well established as a tool to interpret simulation results, since molecules are complicated in their structures and mutual interactions. As a probe to study such molecular interactions, electrostatic fields are considered to be useful. However, since they are given as 3D vector fields having cusps in the fields, conventional drawing techniques are not applicable. In this article, two new approaches are presented to visualize the electrostatic fields of molecules. One is an extension of topological skeletons, by which interactions between atoms having opposite charges are expressed, which is not shown with the conventional methods. The other is to define new functions called selective functions to select regions of interest only from the geometrical features of the fields. Furthermore, from the definition of the new functions, mathematical relations between the topological skeletons and selective functions are discussed. An example is presented in applications to chemical reactions to show how the scheme is used. Copyright © 2001 John Wiley & Sons, Ltd.     

二维包装结构图的三维面模型构造

提出了一种从包装盒三维平面图到三维盒形结构的构造方法,首先给出包装结构的二维平面图约束模型,然后给出包装结构控制图,包结构生成树是及连带子权地揎义,根据二维设计生成的平面线框图,自动抽取盒型表面,构造包装结构控制民包结构树,然后,提出以包装结构生成树为基础的建立包装盒三维面模型结构的算法,最后,讨论模型构造中的预处理问题,贴图是坐标映射问题及关系的实现     

基于三维坐标修正的改进型3DDV-Hop定位算法

针对传统3DDV-Hop算法对未知节点定位误差较大的问题,研究人员提出了各类基于跳数、跳距计算方法进行改进的定位算法,但这些算法中对跳数、跳距计算的改进方法有待优化且未二次求精未知节点坐标;为此,提出一种基于三维坐标修正的改进型3DDV-Hop定位算法,该算法通过为节点设定3类通信半径以及跳距加权以减少跳数、跳距计算误差,并构建正方体交叉区域对未知节点坐标进行二次求精。通过实验结果对比分析可知：本文所提基于三维坐标修正的改进型3DDV-Hop定位算法对未知节点平均定位误差确有显著降低。     

Extending distortion viewing from 2D to 3D

Addresses the visual exploration of 3D information layouts. Several visual exploration techniques have been proposed for 2D information layouts. Many of these try to take advantage of humans' natural visual pattern-recognition abilities to understand global relationships while simultaneously integrating this knowledge with local details. This desire for detail-in-context views (also called fisheye, multiscale and distortion views) has fueled considerable research in the development of distortion viewing tools. Generally, these tools provide space for magnification of local detail by compressing the rest of the image. In considering a possible detail-in-context view for 3D layouts, we first examine 2D distortion techniques, bearing in mind the particular 3D problem of occlusion. Comparing 2D and 3D information layout adjustment tools leads directly to a 3D visual access tool that clears a line of sight to any region of interest. While our technique can extend to any type of 3D information display, we focus on graphs     

矢量与栅格结合的三维地质模型编辑方法

三维地质模型主要通过剖面构造．自动建模方法要求这些剖面基本平行,并且相邻剖面地质体的差别不能过大．本文针对剖面数据较少且不平行的情形,设计了人机交互的三维地质模型构造方法,利用普通多面体栅格化算法和由Marching Cubes算法得到的光栅矢量化,实现了光栅和矢量模型的相互转换．在保证模型间拓扑正确的基础上,提高了地质模型的编辑效率,并在实践中得到了检验．     

Embodied interaction with a 3D versus 2D mobile map

In comparison to 2D maps, 3D mobile maps involve volumetric instead of flat representation of space, realistic instead of symbolic representation of objects, more variable views that are directional and bound to a first-person perspective, more degrees of freedom in movement, and dynamically changing object details. We conducted a field experiment to understand the influence of these qualities on a mobile spatial task where buildings shown on the map were to be localized in the real world. The representational differences were reflected in how often users interact with the physical environment and in when they are more likely to physically turn and move the device, instead of using virtual commands. 2D maps direct users into using reliable and ubiquitous environmental cues like street names and crossings, and 2D better affords the use of pre-knowledge and bodily action to reduce cognitive workload. Both acclaimed virtues of 3D mobile maps—rapid identification of objects and ego-centric alignment—worked poorly due reasons we discuss. However, with practice, some 3D users learned to shift to 2D-like strategies and could thereby improve performance. We conclude with a discussion of how representational differences in mobile maps affect strategies of embodied interaction. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Constructing a 3D individualized head model from two orthogonal views

A new scheme for constructing a 3D individualized head model automatically from only a side view and the front view of the face is presented. The approach instantiates a generic 3D head model based on a set of the individual's facial features extracted by a local maximum-curvature tracking (LMCT) algorithm that we have developed. A distortion vector field that deforms the generic model to that of the individual is computed by correspondence matching and interpolation. The input of the two facial images are blended and texture-mapped onto the 3D head model. Arbitrary views of a person can be generated from two orthogonal images and can be implemented efficiently on a low-cost, PC-based platform.     

3D modeling of multiple-object scenes from sets of images

This paper proposes a new approach for multi-object 3D scene modeling. Scenes with multiple objects are characterized by object occlusions under several views, complex illumination conditions due to multiple reflections and shadows, as well as a variety of object shapes and surface properties. These factors raise huge challenges when attempting to model real 3D multi-object scene by using existing approaches which are designed mainly for single object modeling. The proposed method relies on the initialization provided by a rough 3D model of the scene estimated from the given set of multi-view images. The contributions described in this paper consists of two new methods for identifying and correcting errors in the reconstructed 3D scene. The first approach corrects the location of 3D patches from the scene after detecting the disparity between pairs of their projections into images. The second approach is called shape-from-contours and identifies discrepancies between projections of 3D objects and their corresponding contours, segmented from images. Both unsupervised and supervised segmentations are used to define the contours of objects.     

The advance from 2D electrostatic to 3D electromagnetic particle simulation

The evolution of a 3D, E-M code from earlier less ambitious codes (and their critical analyses) is presented. The code simulates the interaction of some 10⁶ superparticles with over 10⁵ “superphotons” (field modes in k-space). Particle shaping is done in k-space, isotropically. Interpolation of the fields and their excitation is done with optimally fitted quadratic splines, using a 64³ grid. The field modes are updated with no dispersion error, the particles by a time-centered (optionally relativistic) algorithm. Data management conflicts, arising from the global nature of the field information versus the localization of particle processing, are resolved by means of the partial random accessibility of external storage. Results of trial runs with a uniform magnetised plasma show the simultaneous presence of such widely differing phenomena as Alfvén waves, Whistlers, Landau damping, trapping by electrostatic waves, etc., in the computer model.     

Sensor‐aware Normal Estimation for Point Clouds from 3D Range Scans

Normal vectors are essential for many point cloud operations, including segmentation, reconstruction and rendering. The robust estimation of normal vectors from 3D range scans is a challenging task due to undersampling and noise, specially when combining points sampled from multiple sensor locations. Our error model assumes a Gaussian distribution of the range error with spatially‐varying variances that depend on sensor distance and reflected intensity, mimicking the features of Lidar equipment. In this paper we study the impact of measurement errors on the covariance matrices of point neighborhoods. We show that covariance matrices of the true surface points can be estimated from those of the acquired points plus sensor‐dependent directional terms. We derive a lower bound on the neighbourhood size to guarantee that estimated matrix coefficients will be within a predefined error with a prescribed probability. This bound is key for achieving an optimal trade‐off between smoothness and fine detail preservation. We also propose and compare different strategies for handling neighborhoods with samples coming from multiple materials and sensors. We show analytically that our method provides better normal estimates than competing approaches in noise conditions similar to those found in Lidar equipment.     

二维概念格图形的三维重构研究

介绍了二维概念格图形向三维空间转化和延伸的必要性和现状。通过对传统概念格图形分层定位布局方法的研究与分析,提出并实现了一种新的以具有大量的平行四边形和有向线段为基本特征的概念格在三维空间的自动布局算法,描述了一种基于该算法的二维概念格图形的三维重构机制,有效地解决了节点横向过度扩张的问题并减少了线段交叉,较好地实现了复杂概念格图形的三维可视化,为知识发现和知识处理提供了良好的基础。