Novel Geometrical Voxelization Approach with Application to Streamlines

This paper presents a novel geometrical voxelization algorithm for polygonal models.First,distance computation is performed slice by slice on graphics processing units（GPUs） between geometrical primitives and voxels for line/surface voxelization.A novel solid filling process is then proposed to assist surface voxelization and achieve solid voxelization. Furthermore,using the proposed transfer functions,both binary and anti-aliasing voxelizations are achievable. Finally,the proposed approach can be applied to voxelize streamlines for 3D vector fields using line voxelization.The proposed approach obtains desired experimental results.

THUDosePD:a three-dimensional Monte Carlo platform for phantom dose assessment

Monte Carlo simulations are frequently utilized in radiation dose assessments.However,many researchers find the prevailing computing platforms to be intricate.This highlights a pressing need for a specialized framework for phantom dose evalua-tion.To address this gap,we developed a user-friendly radiation dose assessment platform using the Monte Carlo toolkit,Geant4.The Tsinghua University Phantom Dose(THUDosePD)augments the flexibility of Monte Carlo simulations in dosi-metric research.Originating from THUDose,a code with generic,functional,and application layers,THUDosePD focuses predominantly on anatomical phantom dose assessment.Additionally,it enables medical exposure simulation,intricate geometry creation,and supports both three-dimensional radiation dose analysis and phantom format transformations.The system operates on a multi-threaded parallel CPU architecture,with some modules enhanced for GPU parallel computing.Benchmark tests on the ICRP reference male illustrated the capabilities of THUDosePD in phantom dose assessment,covering the effective dose,three-dimensional dose distribution,and three-dimensional organ dose.We also conducted a voxelization conversion on the polygon mesh phantom,demonstrating the method’s efficiency and consistency.Extended applications based on THUDosePD further underline its broad adaptability.This intuitive,three-dimensional platform stands out as a valuable tool for phantom radiation dosimetry research.

Point Cloud Processing Methods for 3D Point Cloud Detection Tasks

Light detection and ranging(LiDAR)sensors play a vital role in acquiring 3D point cloud data and extracting valuable information about objects for tasks such as autonomous driving,robotics,and virtual reality(VR).However,the sparse and disordered nature of the 3D point cloud poses significant challenges to feature extraction.Overcoming limitations is critical for 3D point cloud processing.3D point cloud object detection is a very challenging and crucial task,in which point cloud processing and feature extraction methods play a crucial role and have a significant impact on subsequent object detection performance.In this overview of outstanding work in object detection from the 3D point cloud,we specifically focus on summarizing methods employed in 3D point cloud processing.We introduce the way point clouds are processed in classical 3D object detection algorithms,and their improvements to solve the problems existing in point cloud processing.Different voxelization methods and point cloud sampling strategies will influence the extracted features,thereby impacting the final detection performance.

Study on the LAI Single Tree Model Based on Terrestrial Laser Scanning

Leaf area index (LAI) is a key parameter for studying global terrestrial ecology and environment and has great ecological significance. How to accurately measure and calculate structural parameters of trees has become an urgent matter. This paper reports the use of terrestrial laser scanning (TLS) as a measurement tool to achieve accurate LAI estimation through point cloud preprocessing measures, the LeWos algorithm, and voxel methods. The accuracy and feasibility of this indirect measurement method were explored. It is found that the single wood structure parameters extracted from TLS have a good linear relationship with manual measurement, and the extraction errors meet the requirements of real-scene conversion. The study also found when the voxel size is consistent with the minimum distance of the point cloud set by TLS instrument, it has a strong correlation with the measured value of canopy analyser. These results lay the foundation for conveniently and quickly obtaining structural parameters of trees, tree growth state detection, and canopy ecological benefit assessment.

Clustering Reference Images Based on Covisibility for Visual Localization

In feature-based visual localization for small-scale scenes,local descriptors are used to estimate the camera pose of a query image.For large and ambiguous environments,learning-based hierarchical networks that employ local as well as global descriptors to reduce the search space of database images into a smaller set of reference views have been introduced.However,since global descriptors are generated using visual features,reference images with some of these features may be erroneously selected.In order to address this limitation,this paper proposes two clustering methods based on how often features appear as well as their covisibility.For both approaches,the scene is represented by voxels whose size and number are computed according to the size of the scene and the number of available 3Dpoints.In the first approach,a voxel-based histogram representing highly reoccurring scene regions is generated from reference images.A meanshift is then employed to group the most highly reoccurring voxels into place clusters based on their spatial proximity.In the second approach,a graph representing the covisibility-based relationship of voxels is built.Local matching is performed within the reference image clusters,and a perspective-n-point is employed to estimate the camera pose.The experimental results showed that camera pose estimation using the proposed approaches was more accurate than that of previous methods.

Monte Carlo calculation of the exposure of Chinese female astronauts to earth’s trapped radiation on board the Chinese Space Station

With the development of China’s crewed space mission,the space radiation risk for astronauts is increasingly prominent.This paper describes a simulation of the radiation doses experienced by a Chinese female voxel phantom on board the Chinese Space Station(CSS)performed using the Monte Carlo N-Particle(MCNP)software.The absorbed dose,equivalent dose,and effective dose experienced by the voxel phantom and its critical organs are discussed for different levels of shielding of the Tianhe core module.The risk of space-radiation exposure is then assessed by comparing these doses with the current risk limits in China(the skin dose limit for short-term low-earth-orbit missions)and the NASA figures(National Council on Radiation Protection and Measurements Report No.98)for female astronauts.The results obtained can be used to guide and optimize the radiation protection provided for manned space missions.

城市地下空间资源质量模糊综合评估与3D可视化

采用模糊综合评估方法,构造了地下空间资源质量评估指标的隶属函数,并确定了隶属度,建立了权重向量与模糊关系矩阵复合运算的模糊综合评估模型.同时提出了基于Grid+Voxel的评估基本单元体空间划分方法.并以北京CBD为例,采用模糊评估模型和基本单元体划分方法,在GeoMo3D系统中进行了地下空间资源质量评估,得到了3D可视化评估结果.结果表明:模糊综合评估和基于Grid+Voxel的基本单元体空间划分能够合理表征地下空间资源质量,是城市地下空间资源质量评估及其3D可视化的一种有效的新方法.

数控加工仿真系统的研究与应用

介绍数控加工仿真系统的整体设计,提出格栅voxel三维实体建模方法,刀具扫描体的生成算法,实现了刀具切削工件过程的动态仿真,并对碰撞检查算法进行了初步的研究.基于以上方法,建立了蓝天数控系统的加工仿真系统,在加工前对加工程序进行验证,在加工时对刀具轨迹的执行、工件的切削过程等进行实时监控.

城市地下空间资源质量评估基本单元体的研究

提出了基于Grid+Voxel的基本单元体划分方法及不同类型属性信息提取的量化模型,有效地解决了地下空间资源质量评估最小近似均质体的3D剖分,及基于基本单元体不同类型的属性信息定量提取问题,修正了传统的以地面为参照的2D平面单元划分方法,是城市地下空间资源质量评估基本分析单元划分的一种有效的新方法。

基于VOXEL-MAN针灸学三维影像浏览器的研究

以腧穴解剖研究成果为基础,将临床常用的18个危险穴位的解剖结构数据融入汉堡大学VOXEL-MAN三维数字化虚拟人体中,开发一套VOXEL-MAN 3D Navigator:Acupuncture运行软件(针灸学三维影像浏览器),动态、三维显示腧穴的层次解剖结构和不同角度针刺所经过的断面解剖结构,并建立相关的知识库体系,能够加深对图像内容的理解,有利于提高临床针刺疗效和避免针刺意外事故的发生,并为针灸提供一种理想直观的多媒体教学手段和方法。

可变Voxel与像素映射相结合的图像建模算法

图像建模在军事遥感图像建模、医学人体器官建模、虚拟现实、增强现实等多个领域应用前景广阔。为提高雕刻算法效率,减少图像建模的时间开销,提出了可变Voxel与像素映射相结合的高效空间雕刻图像建模算法,该算法既可以快速雕刻掉物体以外的空间又不用判别可见面就可以快速获得每个表面Voxel的所有可见像素。实验结果表明,该算法在像素映射算法的基础上进一步提高了图像建模速度。

融合中医知识库的虚拟针灸三维浏览器

目的建立融合中医知识库的虚拟针灸三维浏览器,实时显示腧穴的三维解剖结构并模拟针刺过程,实现人机交互操作。方法 在腧穴三维解剖结构的显示基础上,结合语义网络法设计的中医知识库体系,利用VOXEL MAN的脚本控制系统设计动画脚本,生成QTVR格式的智能双层动画,将人体图像内容和中医知识库有机融合。通过浏览器界面,对动画进行交互式调用,模拟针刺的过程。结果 以哑门穴为例,虚拟针刺智能动画清楚地显示了腧穴的解剖结构,直观地表达了进针层次和进针意外。结论 虚拟针灸三维浏览器逼真地展现了虚拟针刺,详细地描述了针灸层次解剖学和断面解剖学知识。

基于压缩Voxel模型的五坐标数控加工仿真新方法

文章介绍了一种基于压缩Voxel模型的五坐标数控加工仿真新方法。该方法采用压缩Voxel模型表示数控加工工件模型和刀具空间扫描体模型,计算机内部存贮空间小,布尔操作简单、速度快。通过MarchingCubes方法提取数控加工仿真工件表面三角网格模型并进行图形显,提高了仿真工件显示质量。文章同时提出了一种基于压缩Voxel模型的刀具空间扫描体构造新方法,通过构造基本几何体球体、圆柱体、圆环体、锥形体和鼓形体的空间扫描体,完成各种加工刀具棒刀、球头刀、环形刀、锥形刀和鼓形刀空间扫描体压缩Voxel模型。该方法在《基于压缩Voxel模型的五坐标数控加工仿真系统》中得到了应用,仿真结果三维信息完备,操作人员可从任意方向观察、验证仿真结果,克服了现有五坐标数控加工仿真方法和商品化软件系统的不足,该方法是虚拟数控加工的关键技术。

基于压缩Voxel模型的整体涡轮叶盘五坐标数控电火花加工仿真验证

提出了基于压缩Voxel模型的整体涡轮叶盘五坐标数控电火花加工仿真、验证新方法.该方法首先构造整体涡轮叶盘仿真工件、成型电极压缩Voxel模型,再根据数控加工轨迹构造成型电极扫描体,最后在三维虚拟空间完成加工过程仿真.利用Marching Cubes方法提取仿真工件表面三角网格,增强了仿真工件显示质量和速度.通过仿真工件压缩Voxel模型与标准CAD模型的三维对比实现了仿真结果分析验证.该方法在某航天火箭发动机整体涡轮叶盘五坐标数控电火花加工编程仿真与验证中得到了应用,效果良好.

二尖瓣和瓣环的Voxel模型三维重建超声显像及其在二尖瓣脱垂中的应用

本文旨在评价经食管体元模型动态三维重建超声显像在二尖瓣脱垂诊断中的价值.研究对象为22例门诊和住院心血管病患者,男12例,女10例,年龄27～56岁,平均40.6±9.3岁,其中三尖瓣正常者12例,经手术证实的二尖瓣脱垂患者10例.图像采集选用美国HewlettPackard Sonos 2500多功能超声诊断仪和5MHz多平面经食管探头.动态三维超声重建采用德国Tomtec计算机工作站.12例二尖瓣正常者和10例二尖瓣脱垂者均能耐受经食管三维超声检查,获得满意的三维图像.用提取法对收缩期二尖瓣环进行三维重建,可得到一静态、立体的二尖瓣环形态.其前叶侧和后叶侧瓣环最高,左右交界侧瓣环最低,整个二尖瓣环呈一立体“马鞍”形,正常组和脱垂组二尖瓣环形态相似.10例二尖瓣脱垂者均能立体显示病变瓣膜的形态特征.从左房往左室方向观察,在心脏收缩期,脱垂部位象“伞面”状飘向在心房,并可精确显示二尖瓣脱垂累及前叶、后叶、前后叶均累及的情况,以及脱垂的具体部位.此外,三维重建后还能直接测量瓣叶脱垂的横径和纵径,明确脱垂大小.结果与术中所见相似.经食管体元模型动态三维重建超声显像能够正确诊断二尖瓣脱垂,且无假阳性和假阴性,具有临床推广意义.

An Algorithm for Voxelizing Non-manifold Triangle Geometry

Taking advantage of the characteristic of distance field and octree, we brought up a method which can discrete any triangle-geometry into voxel. As many triangles used for cutting simulation are unoriented, non-manifold or self-intersecting, which leads to ambiguity in mathematical terms. The algorithm firstly computes sign distance field and use the threshold value to reconstruct the surface, which is very close to the original mode. At last, the reconstructed surface is voxelized. Also we can produce voxelized model which is suitable for cutting simulation.

VOXEL模型样本在ICT仿真中的应用

仿真检测样本模型的研究是CT仿真成像系统研究的一个重要方面,以往所应用的简单体素定义方法和CAD软件造型定义方法等在一定程度上不能够完全满足目前多种多样的零件类型和材料类型,因此本文将基于体素(VOXEL)模型的功能梯度材料(FGM)建模方法引入ICT仿真系统的样本模型研究中,建立了基于VOXEL的非均质材料仿真样本模型,使之能够在当前复合材料等新型材料广泛应用的前提下,较真实地模拟现实中的检测样本,并在CBVCT仿真原型软件中加以应用,取得了较好的结果。

基于Voxel改进模型的数控三维实体建模及显示

传统的Voxel模型在处理多轴数控切削仿真时,不仅在判断是否发生切削上会耗费大量的运算时间,而且数据点的存储也占据了较大的内存空间,不能满足实时快速仿真的要求;在压缩体素模型构造方法中,虽然能够满足多轴数控切削仿真的要求,且存储空间较小,模型重构速度较快,但是在切削判断上的布尔运算量较大,间接影响了数控仿真的实时性。针对以上方法的不足,提出一种基于Voxel改进模型的三维实体建模方法,在显示速度和切削判断上都能够较好地满足数控实体仿真的实时性。

基于三维建模的南京江北新区地下空间资源质量评价

城市地下空间资源开发在城市发展中发挥着重要作用,基于三维建模的城市地下空间资源质量评价为城市地下空间资源利用和开发提供重要支撑。本文以南京江北新区为例,基于30 m×30 m×1 m的Voxel单元处理地质数据,构建地下空间资源质量评价三维地质模型,从工程地质、水文地质等方面选取地下空间资源质量评价指标,利用三维插值、三维空间统计等方法对评价指标进行分析,基于层次分析法和模糊综合评价法得到地下空间资源质量的三维可视化评价结果。研究表明:研究区西部地下空间资源质量较高,东部较低,相关成果可为南京江北新区地下空间规划和可持续开发提供参考。