基于立体视觉的影像多视点建模方法探讨

随着GIS用户对地理信息可视化性能要求的不断提高,虚拟地理场景的景物实体建模方法成为VRGIS领域的热点问题之一。本文探讨了一种基于立体视觉的影像多视点建模方法,包括景物实体表面影像纹理的采集和重建。影像纹理采集方面,提出了根据景物实体形状和景物实体表面纹理分布特点分配采集点的纹理采集方法。影像纹理重建方面,根据多幅影像对应特征点创建采样点模型,最后与几何模型进行空间配准,创建景物实体模型。以一实例进行实验论证,实验结果表明,该建模方法能够有效的提高虚拟地理环境中模型的真实感。     

Color correction of texture images for true photorealistic visualization

Photorealistic visualization combines 3-D geometric models with their texture images to render the virtual world. This paper points out that the texture images should be radiometrically corrected to achieve a true realistic appearance. Such a correction should include not only the color adjustment among images of the same object, but also the shade variation caused by the illumination change. The objective of this study is to correct the input texture images such that their shade varies when being rendered under different illumination directions. To achieve this goal we first apply the specular-to-diffuse mechanism based on the dichromatic reflection model to remove the specular component from the texture image. The resultant diffusion-only image then undergoes a shade correction to produce a normalized shade-free texture image. In the final step, shades under any illumination are produced to achieve a true photorealistic effect. Presented in the paper are the principles and methods for such corrections, along with a performance evaluation based on the graphic and numerical results for roof texture images.     

倾斜影像的三维纹理快速重建

针对三维城市模型重建,提出了一种利用倾斜影像实现城市模型纹理快速重建的方法。该方法基于摄影测量计算机视觉理论,在事先处理得到城市建筑物数字表面模型的基础上,利用共线方程计算物方与像方的几何投影关系,获得建筑物的三维信息与纹理信息。通过一定的最优算法选择出地物面的理想纹理,实现城市建筑物纹理的自动提取及稠密建筑物纹理的遮挡处理。真实影像纹理重建的结果表明:应用本文方法进行三维城市模型纹理重建具有自动化程度高、效果逼真、成本低的特点,为快速、大面积的城市真三维模型纹理重建提供了一种有效的实现途径。     

A multi-sensor approach to creating accurate virtual environments

Creating virtual environment models often requires geometric data from range sensors as well as photometric data from CCD cameras. The model must be geometrically correct, visually realistic, and small enough in size to allow real-time rendering. We present an approach based on 3D range sensor data, multiple CCD cameras, and a colour high-resolution digital still camera. The multiple CCD cameras provide images for a photogrammetric bundle adjustment with constraints. The results of the bundle adjustments are used to register the 3D images from the range sensor in one coordinate system. The images from the high-resolution still camera provide the texture for the final model. The paper describes the system, the techniques for the registration of the 3D images, the building of the efficient geometric model, and the registration and integration of the texture with a simplified geometric model.     

利用摄像机构建数码城市模型

介绍了将多张数码影像镶嵌拼接成“虚拟单像”的方法,解决了摄像机数码影像分辨率不高的问题,实现了城市建筑物、主要装饰物和地面景物的三维模型重建,对已有地形图而无合适航空影像的地区构成了数码城市模型,取得了有益的实验结果。     

3维景观快速建模技术研究

地表3维景观几何对象经过模型化后,都存储在计算机中,只有将其模型进行可视化,才能看到虚拟模型化后的地物景观.本文主要讨论了利用Creator,采用纹理和贴图技术、LOD模型、动态多分辨率的纹理与影像优化技术,提高3维模型的表达,加强可视化效果.     

融合深度相机点云与光学影像的室内三维建模

当前室内三维建模的纹理映射工作主要依赖人工完成,工作量大、处理效率低,且对建模后室内环境的变更难以实现及时更新,导致室内模型纹理存在不真实甚至错误的现象。对此,提出一种室内三维模型纹理手机图片的自动更新方法,该方法主要以手机拍摄的图片为数据源,首先利用智能手机传感器获取拍摄图片的位姿参数,进而通过室内场景理解技术提取图片空间中的三维布局结构,最后与几何模型进行坐标点匹配解算纹理坐标,实现手机图片到三维几何模型的自动纹理映射。实验结果表明,该方法能够利用手机图片数据实现室内环境下的三维模型纹理自动生成及动态更新,有效提高室内三维场景表达的真实性。     

室内三维场景纹理手机图片的自动更新方法

当前室内三维建模的纹理映射工作主要依赖人工完成,工作量大、处理效率低,且对建模后室内环境的变更难以实现及时更新,导致室内模型纹理存在不真实甚至错误的现象。对此,提出一种室内三维模型纹理手机图片的自动更新方法,该方法主要以手机拍摄的图片为数据源,首先利用智能手机传感器获取拍摄图片的位姿参数,进而通过室内场景理解技术提取图片空间中的三维布局结构,最后与几何模型进行坐标点匹配解算纹理坐标,实现手机图片到三维几何模型的自动纹理映射。实验结果表明,该方法能够利用手机图片数据实现室内环境下的三维模型纹理自动生成及动态更新,有效提高室内三维场景表达的真实性。     

Automated reconstruction of 3D models from real environments

This paper describes an integrated approach to the construction of textured 3D scene models of building interiors from laser range data and visual images. This approach has been implemented in a collection of algorithms and sensors within a prototype device for 3D reconstruction, known as the EST (Environmental Sensor for Telepresence). The EST can take the form of a push trolley or of an autonomous mobile platform. The Autonomous EST (AEST) has been designed to provide an integrated solution for automating the creation of complete models. Embedded software performs several functions, including triangulation of the range data, registration of video texture, registration and integration of data acquired from different capture points. Potential applications include facilities management for the construction industry and creating reality models to be used in general areas of virtual reality, for example, virtual studios, virtualised reality for content-related applications (e.g., CD-ROMs), social telepresence, architecture and others. The paper presents the main components of the EST/AEST, and presents some example results obtained from the prototypes. The reconstructed model is encoded in VRML format so that it is possible to access and view the model via the World Wide Web.     

基于航空影像的屋顶半自动重建研究

以航空影像为数据源,设计了一套完整的屋顶快速半自动建模方案。整个建模流程可分为数据获取、数据预处理、几何建模、纹理映射4个阶段。在数据获取阶段,定义了适合于后续建模的两种房屋的屋顶编码方式。在几何建模阶段,利用带约束条件的Delaunay三角构网来构建复杂屋顶几何结构。在纹理映射阶段,提出了一种纹理优化选择算法,选择最佳纹理进行贴图。实验结果表明,此半自动建模方法重建屋顶模型正确率高,纹理贴图精度满足要求。     

基于ICP方法缺乏纹理物体三维曲面模型的匹配

对缺乏纹理物体建立三维模型,关键的难度在于缺乏特征点和点的坐标获得。本文采用ICP算法来对物体进行匹配,当特征点不足时,ICP算法是一个很适用的匹配方法,只需要对物体的给定点寻找最近点。为了计算目标点的坐标,利用投影器投射清晰稳定的纹理到缺乏纹理物体的表面,然后CCD相机对物体进行拍摄。通过线检测和空间前方交会解算出物体部分模型表面的空间点;并使用无需控制点的ICP方法对相互重叠的部分模型进行匹配,从而完成物体的三维重建。实验证明ICP方法对缺乏纹理物体的三维曲面匹配有效。     

积分型非线性平差模型及其在超分辨率图像重建中的应用

超分辨率图像重建过程就是对同一目标进行多次观测,获取多幅低分辨率影像,利用低分辨率影像求取目标的真实影像,即求取高分辨率影像的过程。这一过程与测绘领域中对同一对象进行观测,用测量平差求取对象最佳值的过程类似。本文尝试用测量平差的方法来解决超分辨率重建的问题。文中首先建立了超分辨率重建的积分型非线性平差模型,提出了用二次函数将平差模型中的积分函数参数化,用最小二乘平差方法求解。基于所提出的平差方法,制定了图像重建的具体策略。该方法可以定量分析成果的好坏,可以成功避免出现病态问题等。试验结果表明,相对于传统的超分辨率重建方法获得重建图像的视觉效果有较大的提高,而且其峰值信噪比及结构相似性指数也有很大的提高,因此方法可靠且可行。     

An automatic mosaicking method for building facade texture mapping using a monocular close-range image sequence

This paper presents an automatic mosaicking method for generating building facade textures from a monocular close-range digital image sequence. The process begins with the computation of the camera parameters (except the coordinates of the projective center), which are determined by combining vanishing point geometry with constraints of a straight line bundle as well as prior information of parallel lines in object space. The raw images are later rectified for the purpose of eliminating their salient geometric distortion. Next, automatic retrieval of the relevant image segment is implemented using the detecting range variance by means of the histogram of projective differences between the corresponding points for each of the facades from the raw image sequence. A strip model of the least-squares adjustment, which is similar to the strip block adjustment in aerial triangulation, is employed to determine the spatial alignment of each of the image segments in order to generate the facade textures from the relevant image segments. Afterwards, the entire building facade texture is mosaicked by ortho-image generation. Two refining strategies are proposed to optimize the mosaic result. One is refining the mosaic region where corresponding points are difficult to match but plenty of horizontal lines are available, and the constraint of corresponding horizontal lines is introduced to implement this process. The other strategy is to refine the unsatisfactory mosaic region by densifying the corresponding points by means of the spatial alignment of the relevant image segment computed by the strip method. The experimental results indicate that this method is widely applicable and compares well with other reported approaches with regard to automation level and applicability, for uncalibrated images as well as images with large geometric distortions.     

基于物体成像轮廓的视觉测量与重建

提出一种基于物体的数学模型与成像轮廓进行物体3维视觉测量与重建的方法。该方法主要针对具有规则几何形状的物体,根据被测物体的数学描述和被测物体的轮廓与其在影像上的投影二者的位置关系对物体进行精确的3维测量与重建,得到几何体的空间位置与尺寸参数。对工业零件的基本几何形状圆柱、圆球、立方体等进行实验,结果表明该方法是可行的。     

城市景观三维模型库的原理、构建及应用

随着“数字城市”建设的兴起,如何实现城市景观的精确三维重建正成为目前的研究热点。现实世界的复杂性决定了对其进行数字化三维表达的复杂性,为实现城市景观的快速三维重建,本文提出建立城市景观三维模型库的思路。基于城市地物人工构造所具有的相似性特征,将其进行系统性的总结归纳,为不同地物的建模服务。本文设计了由建筑物特征库、建筑物纹理库、地面覆盖纹理库和独立地物模型库组成的城市模型库结构,并通过在若干三维数字城市工程中的实际应用对具体构建方法及使用效果进行了研究。     

数码城市空间数据模型与可视化研究

提出了一种新的基于三维矢量图形、数字地面模型与数字地面正射影像相结合的数码城市空间数据模型,介绍了基于这一模型的软件平台原型--CCGIS,并对未来数码城市构建技术进行了分析与展望。     

仅用虚拟控制点的超大区域无控制区域网平差

利用光学卫星影像进行无控制测图是摄影测量追求的目标。针对超大区域无控制测图的需求,本文提出了一种以单景影像为平差单元,基于虚拟控制点的光学卫星影像超大规模无控制区域网平差方法。该方法利用待平差影像的初始RPC模型生成虚拟控制点,并将其作为带权观测值引入平差模型中以改善平差模型的状态,克服了在无控制点条件下平差精度不稳定、误差过度累积引起的网的扭曲变形等问题。为了验证本方法的有效性和精度,利用资源三号卫星获取的覆盖全国的26 406景影像进行区域网平差试验,并利用全国范围内分布的约8000个高精度控制点对平差后自动生产的DOM和DSM产品的几何精度进行验证。试验结果表明,平面和高程中误差均达到了4m以内,同时,区域网内部相邻影像之间的几何拼接精度优于1个像素,满足无缝拼接的要求。     

附加视线向量修正的卫星影像区域网平差

针对传统有理函数模型(RFM)区域网平差方法局限于姿态和轨道测量误差小、相机视场角小及影像交会角良好的情况,提出了附加视线向量修正的卫星影像区域网平差方法。首先利用影像附带的有理多项式系数(RPC)计算出像元视线向量,其次根据该视线向量恢复成像时刻虚拟位置和姿态信息,然后对恢复的虚拟位置和姿态构建误差补偿模型,最后通过最小二乘方法整体解算模型参数和连接点物方坐标。该方法从系统误差产生的原因构建补偿模型,可以规避传统区域网平差方法的近似假设和条件限制。通过对模拟数据以及多套测绘卫星和非测绘卫星数据进行试验的结果表明,该方法处理大姿态角误差、大视场角以及弱交会角等各种严苛条件下的卫星影像能达到比传统方法更好的效果。     

An appearance‐preserving simplification method for complex 3D building models

The simplification of 3D building models to effectively reduce model complexity and improve rendering efficiency is an important component of 3D GIS. To reduce the data volume while preserving the model appearance, this article proposes a novel simplification method for complex 3D building models. Texture discontinuities are addressed by developing a new data model that records the mapping relation between the texture coordinates of each vertex and its neighboring triangles. The surface mesh of the building model is then segmented into regions, guided by topology and appearance. Finally, the mesh segmentation information is used to derive an improved error metric that considers both geometric and texture errors, and the texture coordinates are adjusted after each simplification operation. A series of comparative experiments alongside traditional methods demonstrates that our approach achieves a good balance between geometric fidelity and texture preservation, and produces simplified 3D building models with better visual quality.     

GF-2影像城市地物分类方法探讨

GF-2影像具有较高的分辨率和丰富的光谱、几何及纹理信息。为了深入探索GF-2影像城市地物分类方法,本文以四川省隆昌县城为研究区,提出了一种基于最优尺度和规则的面向对象分类法。在影像分割的基础上,通过构建评价函数,并结合最大面积法选取最优尺度,进而构建分层体系,提取影像的光谱、几何及纹理特征建立规则并分类,且将其与单尺度下的面向对象和基于像素分类法进行对比分析。结果表明,本文方法的总体精度和Kappa系数分别为93.33%和0.92。