下视SAR数据3维表面重建

目的 合成孔径雷达(SAR)因成像方法、几何角度等原因使得采集到的数据具有稀疏性及残缺性,如果直接用其进行建模,不能真实地还原物体。针对下视SAR数据的特点,提出一种在建模过程中能够自动修补稀疏及残缺数据的重建方法。方法 首先引入大津法对3维SAR数据进行预处理,然后将2维图像分割方法中的Chan-Vese模型推广应用到下视SAR数据的表面重建中,在初始表面及轮廓指示函数的求取过程中引入距离函数和内积函数。结果 将本文方法与等值面抽取法的重建结果进行比较,本文方法在重建的过程中能够自动修补空洞,重建出的模型表面更加光滑,能更加真实地反映原物体的特征。结论 可以将本文方法推广应用到稀疏及残缺SAR数据的建模中。     

3D reconstruction and classification of natural environments by an autonomous vehicle using multi-baseline stereo

In natural outdoor settings, advanced perception systems and learning strategies are major requirement for an autonomous vehicle to sense and understand the surrounding environment, recognizing artificial and natural structures, topology, vegetation and drivable paths. Stereo vision has been used extensively for this purpose. However, conventional single-baseline stereo does not scale well to different depths of perception. In this paper, a multi-baseline stereo frame is introduced to perform accurate 3D scene reconstruction from near range up to several meters away from the vehicle. A classifier that segments the scene into navigable and non-navigable areas based on 3D data is also described. It incorporates geometric features within an online self-learning framework to model and identify traversable ground, without any a priori assumption on the terrain characteristics. The ground model is automatically retrained during the robot motion, thus ensuring adaptation to environmental changes. The proposed strategy is of general applicability for robot’s perception and it can be implemented using any range sensor. Here, it is demonstrated for stereo-based data acquired by the multi-baseline device. Experimental tests, carried out in a rural environment with an off-road vehicle, are presented. It is shown that the use of a multi-baseline stereo frame allows for accurate reconstruction and scene segmentation at a wide range of visible distances, thus increasing the overall flexibility and reliability of the perception system.     

多视三维重构中连续能量模型的凸优化

利用融合了轮廓线及体视的序列图像信息,提出了一个面向多视三维重构的稳健能量模型;为了适配于可视性约束,提出一种针对该能量模型的连续全局优化方法;为了保证栅格连通性选择的一致性及独立性,实施了全局连续优化的超松弛离散化。实例证明,该方法的实用性好,极大地减少了算法处理的内存开销,实现了在更高分辨率上有效的多视重构。     

用单数码相机实现物体表面的三维重建

根据由运动重建物体结构的原理,设计了一个简便易操作的三维重建系统,具体做法是:先用张氏标定法求得内参数矩阵,然后在两个不同的未知位置拍摄物体得到两幅图像,经立体匹配后,利用图像特征点的对应关系求解基本矩阵和本质矩阵,分解本质矩阵获得两个拍摄位置确定的摄像机运动参数(旋转矩阵和平移向量),进而求出相机在两个位置的投影矩阵,最后用三角法计算出物体表面特征点的三维坐标并在OpenGL中重建物体表面.和传统的立体视觉系统相比,本系统只需要一台数码相机和平面方格模板就可以实现三维重建,因此适用于普通相机用户.     

Detecting changes in surface soil moisture content using differential SAR interferometry

The feasibility of measuring changes in surface soil moisture content with differential interferometric synthetic aperture radar (DInSAR) has received little attention in comparison with other active microwave techniques. In this study, multi-polarization C- and L-band DInSAR is explored as a potential tool for the measurement of changes in surface soil moisture in agricultural areas. Using 10 ascending phased array L-band SAR (PALSAR) scenes acquired by the Japanese Advanced Land Observing Satellite (ALOS) and 12 descending advanced SAR (ASAR) scenes acquired by the European ENVISAT satellite between July 2007 and November 2009, a series of 27 differential interferograms covering a common study area over southern Ireland were generated to investigate whether small-scale changes in phase are linked to measured soil moisture changes. Comparisons of observed mean surface displacement and in situ mean soil moisture change show that C-band cross-polarization pairs displayed the highest correlation coefficients over both the barley (correlation coefficient, r = 0.51, p = 0.04)- and potato crop (r = 0.81, p = 0.003)-covered fields. Current results support the hypothesis that a soil moisture phase contribution exists within differential interferograms covering agricultural areas.     

基于标准差的地形三维表面模型建立方法*

针对二维数据域的Delaunay三角剖分推广到空间时存在的关键问题,提出一种基于标准差的地形三维表面模型建立算法.与空外接圆准则相比,该算法在计算时考虑了附加高程信息,引入标准差作为构网判断准则.剖析了标准差的含义,为什么使用标准差以及基于标准差的剖分准则,最后给出基于标准差的地形三维表面模型建立算法的具体步骤,并通过一个具体实例对算法进行了验证.     

三维地形模型流式传输方法

为满足基于网络的大规模地形漫游系统中有限的网络带宽与海量地形数据之间的矛盾,提出了一种三维地形流式渐进传输方法。该方法在服务器端对地形数据进行预处理,首先将地形数据进行分块,再对分块后的数据进行小波变换,最后用多级树集合分裂(SPIHT)算法将变换后的数据组织成多条渐进码流。客户端在运行时根据视点的位置,漫游的速度和方向确定周围各地块的传输规则,使各地块的传输量进行自适应调整,同时采用二级缓存机制缓解网络拥塞时数据供应压力。实验表明,该方法能很好地支持客户端基于GPU的多分辨率地形构造并在各种网络带宽情况下保持较高的绘制帧率,保证网络交互绘制的实时性。     

自适应的三维分形地形重建算法研究*

针对常规三维分形地形重建算法具有的速度慢、插值点分布不均匀、参数设置复杂等缺点,提出自适应的三维分形地形重建算法。该算法根据地形的起伏特征自动确定垂直压缩因子,根据子域面积进行均匀插值。实验结果表明,该方法插值效率更高,所获得的插值曲面更加真实,与常规分形插值相比具有一定的优越性。     

Constrained 3D shape reconstruction using a combination of surface fitting and registration

We investigate 3D shape reconstruction from measurement data in the presence of constraints. The constraints may fix the surface type or set geometric relations between parts of an object's surface, such as orthogonality, parallelity and others. It is proposed to use a combination of surface fitting and registration within the geometric optimization framework of squared distance minimization (SDM). In this way, we obtain a quasi-Newton like optimization algorithm, which in each iteration simultaneously registers the data set with a rigid motion to the fitting surface and adapts the shape of the fitting surface. We present examples to show the applicability of our method to constrained 3D shape fitting for reverse engineering of CAD models and to high accuracy fitting with kinematic surfaces, which include surfaces of revolution (reconstructed from fragments of archeological pottery) and spiral surfaces, which are fitted to 3D measurement data of shells. Our optimization algorithm can combine registration of multiple scans of an object and model fitting into a single optimization process which is shown to be superior to the traditional procedure, which first registers the data and then fits a model to it.     

Coverage path planning with unmanned aerial vehicles for 3D terrain reconstruction

Three-dimensional terrain reconstruction from 2D aerial images is a problem of utmost importance due its wide level of applications. It is relevant in the context of intelligent systems for disaster managements (for example to analyze a flooded area), soil analysis, earthquake crisis, civil engineering, urban planning, surveillance and defense research.It is a two level problem, being the former the acquisition of the aerial images and the later, the 3D reconstruction. We focus here in the first problem, known as coverage path planning, and we consider the case where the camera is mounted on an unmanned aerial vehicle (UAV).In contrast with the case when ground vehicles are used, coverage path planning for a UAV is a lesser studied problem. As the areas to cover become complex, there is a clear need for algorithms that will provide good enough solutions in affordable times, while taking into account certain specificities of the problem at hand. Our algorithm can deal with both convex and non-convex areas and their main aim is to obtain a path that reduces the battery consumption, through minimizing the number of turns.We comment on line sweep calculation and propose improvements for the path generation and the polygon decomposition problems such as coverage alternatives and the interrupted path concept. Illustrative examples show the potential of our algorithm in two senses: ability to perform the coverage when complex regions are considered, and achievement of better solution than a published result (in terms of the number of turns used).     

Motion control of a quadruped robot in unknown rough terrain using 3D spring damper leg model

This paper presents a simple method to control the motion of a quadruped robot in unknown rough terrain using a full dynamic model. First, using the stiffness control method, the behavior of the four legs is approximated using four 3D spring damper systems. In this way, the dynamic model can be derived in Cartesian space. Based on this model, a control strategy is proposed to preserve the asymptotical stability of the system. In addition, a reflex motion control is introduced to cope with the rotational disturbance of the robot body. Finally, dynamic simulations and experiments of a quadruped walking robot were performed on unknown rough terrain to verify the proposed method.     

Accurate reconstruction of 3D model of a human face using structured light

An automated system for the reconstruction of textured 3D models of human faces has been developed. 3D information is read using the structured lighting used in calibrated projector-camera system. The accuracy of 3D reconstruction is studied experimentally. De Wansa Wickramarante Viktor Klementovich. Born 1983. Graduated from the Moscow State Institute of Radioengineering, Electronics, and Automation (Technical University). Post graduate student of MSIREA. Scientific interests: pattern recognition, biometry, 3D scanners. Author of 5 papers. Awarded the 3 degree diploma at the All-Russian Conference MMRO-13; the incentive diploma at the International Conference ROAI-8-2007. Vladimir Vasilievich Ryazanov. Vladimir V. Ryazanov gratuated from the Moscow Institute of Physical Technology in 1973 and the post-graduate courses at the Computer Center, Academy of Sciences, USSR, in 1976. Received Ph.D. in 1977 (“Computer Science”) and Professor degree in 1994 (“Applications of Mathematical Methods, Mathematical Modeling and Computers in Scientific Investigations”). At the Dorodnicin Computer Center of the Russian Academy of Sciences since 1976. Head of the Situations Recognition Sector in the Department of Recognition Problems and Combinatorial Analysis. Author of approximately 150 papers. Scientific interests: data mining, mathematical models of pattern recognition, classification and forecasting, optimization of recognition and classification models, learning, synthesis of optimal collective solutions in the classification problem, creation of intelligent program systems for data analysis and recognition, and practical applications in technology, medicine, industry. Alexander Vinogradov. Born in 1951. Graduate from Moscow Institute of Physics and Technology in 1974. Kandidat degree in mathematical cybernetics, 1978. Spere of main interests—geometric and algebraic methods in data analysis and image processing. Author of about 50 scientific publications.     

3D reconstruction of a femoral shape using a parametric model and two 2D fluoroscopic images

In medical diagnostic imaging, the X-ray CT scanner and the MRI system have been widely used to examine 3D shapes and internal structures of living organisms and bones. However, these apparatuses are generally large and very expensive. Since an appointment is also required before examination, these systems are not suitable for urgent fracture diagnosis in emergency treatment. However, X-ray/fluoroscopy has been widely used as traditional medical diagnosis. Therefore, the realization of the reconstruction of precise 3D shapes of living organisms or bones from a few conventional 2D fluoroscopic images might be very useful in practice, in terms of cost, labor, and radiation exposure. The present paper proposes a method by which to estimate a patient-specific 3D shape of a femur from only two fluoroscopic images using a parametric femoral model. First, we develop a parametric femoral model by the statistical analysis of 3D femoral shapes created from CT images of 56 patients. Then, the position and shape parameters of the parametric model are estimated from two 2D fluoroscopic images using a distance map constructed by the Level Set Method. Experiments using synthesized images, fluoroscopic images of a phantom femur, and in vivo images for hip prosthesis patients are successfully carried out, and it is verified that the proposed system has practical applications.     

由航空影像自动重建大范围3维地形

目的 针对由航空影像自动生成大范围3维地形的立体模型配准问题,提出一种自动配准全部立体模型的方法,从而生成大范围3维地形。方法 首先由相邻影像构建独立的立体模型;然后根据特征匹配同名点在公共影像上的坐标对应关系,自动提取相邻模型的连接点;通过循环遍历搜索,自动配准全部立体模型,进而构建全航摄区的大范围3维地形。结果 采用两组数据进行实验,结果显示,两组数据全部3维模型的均方配准误差分别为5.20像素和2.63像素。本文方法生成的大范围地形的相对精度较高;对第2组数据的结果采用控制点进行绝对定向,并用检查点进行精度评估,结果显示全部检查点的均方平面和高程误差分别为0.326 m和0.502 m,生成的大范围地形达到了较高的绝对精度。结论 本文方法可自动化执行,仅需输入一系列有一定重叠的航空影像,即可自动生成按一定方式组织的大范围3维地形产品。该方法生成的大范围地形既可用于3维场景浏览,也可用于地形量测,但不适用于由激光扫描获取的点云数据的配准。     

3D model reconstruction using neural gas accelerated on GPU

In this work, we propose the use of the neural gas (NG), a neural network that uses an unsupervised Competitive Hebbian Learning (CHL) rule, to develop a reverse engineering process. This is a simple and accurate method to reconstruct objects from point clouds obtained from multiple overlapping views using low-cost sensors. In contrast to other methods that may need several stages that include downsampling, noise filtering and many other tasks, the NG automatically obtains the 3D model of the scanned objects. To demonstrate the validity of our proposal we tested our method with several models and performed a study of the neural network parameterization computing the quality of representation and also comparing results with other neural methods like growing neural gas and Kohonen maps or classical methods like Voxel Grid. We also reconstructed models acquired by low cost sensors that can be used in virtual and augmented reality environments for redesign or manipulation purposes. Since the NG algorithm has a strong computational cost we propose its acceleration. We have redesigned and implemented the NG learning algorithm to fit it onto Graphics Processing Units using CUDA. A speed-up of 180× faster is obtained compared to the sequential CPU version.     

三维地形板块构造模型的研究

在三维地形实时、快速渲染的研究中,提出了一种板块构造模型。为实现地形板块之间的实时过渡渲染,提出了插槽算法。通过实验,该模型能够解决超大地形的快速访问和渲染问题,适合分布式应用。     

切片级管线表面三维重建

在比较表面重建中的面绘制法和体绘制法以及面绘制中的切片级和体素级两种表面重建方法、分析表面重建流程的基础上,提出了一种计算型值点集的方法,它在计算弯道部分的管线时较为简便。该方法通过二次曲面求管线表面轮廓方程进而求得管线的型值点集。之后用三角网格对型值点集进行拼接来获得管线的表面模型,最后利用图形学的方法对管线表面模型进行绘制,达到管线表面三维重建的目的。文末利用Java3D给出了一个具体的实现。     

三维散乱点云快速曲面重建算法

提出了一种基于Delaunay三角剖分的三维散乱点云快速曲面重建算法。算法首先计算点云的Delaunay三角剖分, 从Delaunay四面体提取初始三角网格, 根据Voronoi体元的特征构造优先队列并生成种子三角网格, 然后通过区域生长的方式进行流形提取。实验结果表明, 该算法可以高效、稳定地重构具有复杂拓扑结构、非封闭曲面甚至是非均匀采样的点云数据。与传统的基于Delaunay的方法比较, 该算法仅需要进行一次Delaunay三角剖分, 无须极点的计算, 因此算法的重构速度快。