基于3D Widgets三维交互快速拾取算法研究

为解决图形、图像在三维交互及深度[10]信息处理过程中所存在的问题,提出了一种以3D Widgets为核心的三维交互框架,并研究了三维交互拾取的多种算法。基于3D Widget[4]的拾取技术能提供给用户交互旋转和交互拾取的功能。实验结果表明,该算法与已有的算法相比,将这些算法其应用在手术模拟三维交互系统中,可以提高用户使用的直观性,还有益于以后的功能扩展。为后续的交互过程奠定基础。本文的创新之处正是在此理论的基础上,将其应用在三维交互中具有重要的价值和意义。     

离散点集3D三角划分算法在裁剪曲面中的实现

提出一种在3D空间直接对曲面离散数据点进行三角网格划分的算法,该方法适用于非封闭曲面、封闭曲面及多连通复杂曲面的离散点集,同时也能处理剪载曲面的离散点集,得到优良的三角网格。在引入边界环融合的概念的基础上,详细阐述算法如何实现对剪载裁曲面离散点集三角划分,并给出应用实例。     

矢量画刷的设计与实现

在计算机上模拟现实中美术工作者使用的画刷一直是二维矢量编辑器必备的功能,本文介绍了如何在计算机上模拟绘图画刷的算法,其思想是将用户通过鼠标输入的一组离散的点转换成具有画刷风格的矢量图形,先对多边形画刷的外形定义,再对画刷的连续移动进行轨迹合成,最后实现特定的形状的画刷的轨迹。在此基础上实现了矩形、斜四边形、圆形画刷的算法设计。本文亦针对稠密的轨迹出现的自环绕现象,提出了反锯齿算法,并减少了自环绕圈数。实验测试结果表明,该算法效果良好,达到了预期目标。     

三维复杂曲面的手绘生成方法

为便于用户在概念设计时快速进行三维形状设计,将变分隐式曲面表示与手绘草图相结合,提出一种三维复杂曲面的交互生成方法.该方法分别采用膨胀变换、曲线交叉变换和弯曲变换,将轮廓、截面和骨架等3种交互笔画扩展生成三维约束点,支持用户以手绘草图方式来控制生成三维曲面的形状;通过对变分隐式曲面函数的局部化来实现曲面混合,保证三维复杂曲面交互生成的实时性.实验结果表明:文中方法能生成多种不同形状的三维复杂曲面,可有效地支持三维复杂形状的"分而治之"构造过程.     

点元表示的参数曲面相切判断与计算

提出了一种基于点元的参数曲面求切新算法,该算法先对曲面进行离散点元采样,通过层次包围盒测试,建立法向包围锥,对判断为可能相切的区域,根据精度自适应动态重采样点元,最后进行求切运算.实验表明,通过对曲面可能相切区域分析检测,能够针对曲面相切的情况在可控误差范围内有效求出切点,算法稳定可靠且易于交互.     

一种隐式曲面交互调整的新方法

提出了一种对隐式曲面形状进行交互调整的新方法,为隐式曲面的调整提供了两种交互工具,分别是对曲面上点的位置调整和法向调整.该方法以调整后的位置和法向为新曲面的插值条件建立目标函数,极小化该目标函数求解曲面参数的变化量,从而确定新的隐式曲面.文中采用拟牛顿法和序列二次规划法(SQP)求解该非线性优化问题.在调整过程中用粒子的方法对隐式曲面进行绘制,实现了对隐式曲面形状的实时交互调整.最后用实例说明了新方法的有效性.     

方程曲面的一种绘制算法

提出了显式方程和参数方程表示的曲面的一种绘制算法,该算法可以绘制任意复杂的方程曲面。首先将方程曲面离散成四边形网格,然后采用消隐算法消除曲面的自隐藏线。消隐算法引入遮挡多边形的概念,利用遮挡多边形判断曲面上离散点的隐藏性,同时将潜在隐藏线段与遮挡多边形求交,从而得到该线段的实际隐藏部分。该绘制算法对以网格模型显示三维物体具有通用性。     

多连通曲面离散点集的3D三角划分算法研究

在对非封闭曲面、简单封闭曲面和多连通封闭曲面的特点进行分析之后,提出了一种多连通封闭曲面离散点集的3D三角划分算法.该算法无须对离散点集所对应的自由曲面进行分片,直接在3D空间根据曲面的形态变化向前逐层推进生成三角网格.算法同时还适用于非封闭曲面和简单封闭曲面两种情形.实验结果表明,该算法的划分效果优良,能够满足曲面重构的需要.     

插值细分曲面三角剖分研究

把三维参数化曲面的离散化算法应用到三角网格表示的离散曲面上。用一种可生成C1阶连续曲面的插值分割技术——改进蝶形算法,重新构造极限面。用推进波前法在物理空间直接离散化,所以不需要进行参数化。     

基于事件交互图的算法与研究

图形用户界面的质量直接影响整个软件系统的有效性和实用性,一般采用提取模型的方法对图形用户界面进行测试,目前常用的模型为事件流图和事件交互图,但是事件流图转换成事件交互图的算法较为复杂,为此,提出一种转换算法,对图形用户界面事件进行明确划分,利用模态窗口事件的特殊性优化原有算法。测试实例结果表明,该算法可用于图形用户界面,且与Memon算法相比,能更高效地获得更准确的数据。     

基于医学图像的三维测量技术研究和实现

针对由序列断层医学图像重建得到的三维图形,提出一种交互式三维测量技术.首先通过光线投射法实现了对三维空间中任意一点的拾取,将用户指定的屏幕二维坐标点转化为立体坐标系下的空间三维坐标.选取空间中两点后即可以对三维重建后的病人器官进行测量,得到较为满意的结果.此外,在原有拾取方法的基础上,作出一定改进,使用户更方便地获取空间中任意一点的坐标.     

Robust normal estimation and region growing segmentation of infrastructure 3D point cloud models

Modern remote sensing technologies such as three-dimensional (3D) laser scanners and image-based 3D scene reconstruction are in increasing demand for applications in civil infrastructure design, maintenance, operation, and as-built construction verification. The complex nature of the 3D point clouds these technologies generate, as well as the often massive scale of the 3D data, make it inefficient and time consuming to manually analyze and manipulate point clouds, and highlights the need for automated analysis techniques. This paper presents one such technique, a new region growing algorithm for the automated segmentation of both planar and non-planar surfaces in point clouds. A core component of the algorithm is a new point normal estimation method, an essential task for many point cloud processing algorithms. The newly developed estimation method utilizes robust multivariate statistical outlier analysis for reliable normal estimation in complex 3D models, considering that these models often contain regions of varying surface roughness, a mixture of high curvature and low curvature regions, and sharp features. An adaptation of Mahalanobis distance, in which the mean vector and covariance matrix are derived from a high-breakdown multivariate location and scale estimator called Deterministic MM-estimator (DetMM) is used to find and discard outlier points prior to estimating the best local tangent plane around any point in a cloud. This approach is capable of more accurately estimating point normals located in highly curved regions or near sharp features. Thereafter, the estimated point normals serve a region growing segmentation algorithm that only requires a single input parameter, an improvement over existing methods which typically require two control parameters. The reliability and robustness of the normal estimation subroutine was compared against well-known normal estimation methods including the Minimum Volume Ellipsoid (MVE) and Minimum Covariance Determinant (MCD) estimators, along with Maximum Likelihood Sample Consensus (MLESAC). The overall region growing segmentation algorithm was then experimentally validated on several challenging 3D point clouds of real-world infrastructure systems. The results indicate that the developed approach performs more accurately and robustly in comparison with conventional region growing methods, particularly in the presence of sharp features, outliers and noise.     

基于细分曲面的三维服装柔性实体模拟

提出一种基于细分曲面的三维服装柔性实体模拟算法，该算法将整个模拟过程分为两个阶段：首先利用四点细分曲面造型方法生成三维服装刚性曲面，然后在刚性曲面基础上通过引入织物的物理模型来模拟三维服装柔性曲面，通过物理和几何模拟方法有机结合，算法有效解决了复杂衣片间的缝合问题，较大地提高了模拟的计算效率，同时，也提出了一种基于细分曲面层次数据结构的碰撞检测算法，有效提高了模拟速度，提出的算法已全部在所开发的三维虚拟服装试衣系统中得以实现，实验结果表明：该算法具有模拟效率高、交互性强和易于计算机实现等优点。     

一种基于位置关系判定的GPU 三维几何图元拾取方法

针对交互式图形应用对拾取在效率、适用范围和拾取信息方面的需求,提出一种 新的基于GPU 的三维几何图元拾取方法。在进行拾取绘制时关闭光栅化,将鼠标位置信息和图 元顶点坐标变换到规范化设备坐标系,通过在几何处理器中判断投影后的二维图元与鼠标或选 择框的位置关系进行命中判定,并利用变换反馈将拾取信息返回应用程序。在提出方法的基础 上,介绍了单体拾取和块拾取的OpenGL 实现。实验表明,该方法的单体拾取效率较基于GPU 的射线相交法有约10%的提升,同时能支持高效块拾取。     

Visualizing diffusion tensor MR images using streamtubes and streamsurfaces

We present a new method for visualizing 3D volumetric diffusion tensor MR images. We distinguish between linear anisotropy and planar anisotropy and represent values in the two regimes using streamtubes and streamsurfaces, respectively. Streamtubes represent structures with primarily linear diffusion, typically fiber tracts; streamtube direction correlates with tract orientation. The cross-sectional shape and color of each streamtube represent additional information from the diffusion tensor at each point. Streamsurfaces represent structures in which diffusion is primarily planar. Our algorithm chooses a very small representative subset of the streamtubes and streamsurfaces for display. We describe the set of metrics used for the culling process, which reduces visual clutter and improves interactivity. We also generate anatomical landmarks to identify the locations of such structures as the eyes, skull surface, and ventricles. The final models are complex surface geometries that can be imported into many interactive graphics software environments. We describe a virtual environment to interact with these models. Expert feedback from doctors studying changes in white-matter structures after gamma-knife capsulotomy and preoperative planning for brain tumor surgery shows that streamtubes correlate well with major neural structures, the 2D section and geometric landmarks are important in understanding the visualization, and the stereo and interactivity from the virtual environment aid in understanding the complex geometric models.     

一种基于序列图像的交互式快速三维重建方法

针对普通数码相机拍摄的序列图像,提出了一种快速的交互式三维重建方法.首先基于SFM技术得到了相机的内外部参数;然后在图像上交互取点以构建逼近物体轮廓的多边形,结合该多边形,利用轮廓跟踪算法提取出精确的外形轮廓;最后通过匹配轮廓点的方式重建出三维模型.实验结果表明该重建方法是快速而有效的.     

基于颜色编码的虚拟树木交互式修剪技术及其实现

为了解决传统方法中存在的三维树木交互式修剪问题,提出一种基于颜色编码的虚拟树木交互式快速修剪方法.首先分析了虚拟树木交互式修剪技术的要求和存在的困难;然后依托自主开发的基于形态特征参数的三维树木建模系统ParaTree,提出一种结合树木层级拓扑结构的快速拾取海量图元的方法,将树木三维模型巧妙地编码为32位RGBA颜色,...     

Integrative 3D modelling of complex carving surface

Modelling of a complex carving surface is the most important process for digitization of art carving such as Chinese classical furniture carving, and it is difficult to be fulfilled. However, a complex 2D curve flower pattern can be easily acquired or drawn by handcraft or a drawing software. This paper presents a quick integrative 3D modeling method of complex carving surface based on a 2D curve flower pattern. The proposed method uses a scanning analysis algorithm, a normal distribution function and a distance function to model and create carving tracks. In this paper, the delamination, combination and interpolation of modelling process are described as well. The provided research method will make the modelling of complex carving surface more intelligent, agile, and will meet the requirement of integrative 3D modelling of digital art carving. Experimental results show that this method is of quick modelling and multi-model effective characteristics with realizable interactive designing and excellent practicability.     

FastV: From-point Visibility Culling on Complex Models

We present an efficient technique to compute the potentially visible set (PVS) of triangles in a complex 3D scene from a viewpoint. The algorithm computes a conservative PVS at object space accuracy. Our approach traces a high number of small, volumetric frusta and computes blockers for each frustum using simple intersection tests. In practice, the algorithm can compute the PVS of CAD and scanned models composed of millions of triangles at interactive rates on a multi-core PC. We also use the visibility algorithm to accurately compute the reflection paths from a point sound source. The resulting sound propagation algorithm is 10–20X faster than prior accurate geometric acoustic methods.     

3D空间复杂楼梯面可视化快速参数建模

空间复杂楼梯面的智能化建模问题是建筑、装饰等行业的难点、热点问题.本文以AutoCAD VBA作为开发工具,给出3D空间复杂楼梯面可视化参数快速建模方法,并对复杂楼梯面的生成算法与技巧进行了研究,使空间复杂楼梯面模型的设计更具敏捷化、智能化和可交互性.开发的设计程序可作为AutoCAD命令嵌入到AutoCAD绘图软件中,以提高用户的设计效率.