避险车道驶入角计算方法评价

避险车道驶入角取值直接影响失控车辆能否安全驶入避险车道。基于车辆动力学仿真采用极限侧向加速度参数评价避险车道驶入角计算方法。首先,通过失控车辆稳定性分析确定车辆极限转弯半径;其次,采用三种驶入角的计算方法分别计算三种车速对应的避险车道驶入角;最后,基于车辆动力学仿真软件TruckSim,分别建立失控车辆和避险车道仿真模型,以极限侧向加速度作为评价指标设计并完成3组车辆稳定性仿真。仿真结果表明:方法二比方法三合理。对于方法二,进一步分析驶入角与主线转弯半径的关系,结果也表明方法二比方法三合理;继续采用极限侧向加速度作为评价指标并进行仿真,优化方法二的驶入角范围并与其它研究对比,结果表明了方法二优化结果的正确性。     

Hallucinating Stereoscopy from a Single Image

We introduce a novel method for enabling stereoscopic viewing of a scene from a single pre‐segmented image. Rather than attempting full 3D reconstruction or accurate depth map recovery, we hallucinate a rough approximation of the scene's 3D model using a number of simple depth and occlusion cues and shape priors. We begin by depth‐sorting the segments, each of which is assumed to represent a separate object in the scene, resulting in a collection of depth layers. The shapes and textures of the partially occluded segments are then completed using symmetry and convexity priors. Next, each completed segment is converted to a union of generalized cylinders yielding a rough 3D model for each object. Finally, the object depths are refined using an iterative ground fitting process. The hallucinated 3D model of the scene may then be used to generate a stereoscopic image pair, or to produce images from novel viewpoints within a small neighborhood of the original view. Despite the simplicity of our approach, we show that it compares favorably with state‐of‐the‐art depth ordering methods. A user study was conducted showing that our method produces more convincing stereoscopic images than existing semi‐interactive and automatic single image depth recovery methods.     

Nonlinear State Estimation and Control for Freeway On‐Ramp Metering

The work presented in this paper deals with freeway ramp metering using a differential flatness concept. Such an approach is deployed in the cases when the traffic data provided by loop detectors (or any measurements device), are partially unknown or missed, and/or the downstream measurement station, located at the vicinity of the controlled ramp, is faulty. The proposed solution rests on the estimation of the main variables using the “revised” method of numerical differentiation, i.e., estimation of the derivative of noisy time signals. Such an algebraic approach, which does not need any integration of differential equations, turns out to be quite robust with respect to perturbations inputs and measurements noises. Convincing numerical simulations are provided using a modified second‐order continuum macroscopic model. Furthermore, a comparative study using the Extended Kalman Filter (EKF), which is the most used in the area of traffic state estimators, is proposed in order to demonstrate the effectiveness of the strategy.     

Superposition of local zoom models and simultaneous calibration for 1D–2D shallow water flows

We address the problem of coupling 2D shallow water equations with 1D shallow water equations (St-Venant equations), as applied to river-floodplain flows. Mathematical coupling conditions are derived classicaly from the 3D Navier–Stokes equations by integrating over the vertical wet section, when overflowing occurs. It leads to extra source terms in the 1D equations. Next we assume to be in a variational data assimilation context, then the optimal control process allows to couple both models and assimilate data simultaneously (Joint Assimilation Coupling algorithms). Two different versions of JAC algorithms are presented and compared. In a numerical test case, we superimpose the local 2D model on the 1D global model. The results show the efficiency of the present simultaneous superposition–assimilation approach.     

河流水质模型求解的Chebyshev正交多项式方法

提出一种考虑弥散时Streeter—Phelps一维稳态河流水质模型Chebyshev正交多项式的近似解法．通过对稳态河流水质模型的非线性高阶微分方程式分析,采用Chebyshev正交多项式对各阶微分和弥散系数D进行近似描述,得到稳态河流水质模型的近似表达式．针对近似模型给出了误差指标,并采用最小二乘对近似式中的未知参数进行估计;同时,对算法的总精度进行了讨论．仿真结果表明,该方法的精度高于多种微分方程数值计算方法(如龙格一库塔),不仅可以提高生化需氧量的计算精度,而且能够大大提高溶解氧浓度计算结果的准确性．     

Spatial-temporal consistent labeling of tracked pedestrians across non-overlapping camera views

Tracking people across multiple cameras with non-overlapping views is a challenging task, since their observations are separated in time and space and their appearances may vary significantly. This paper proposes a Bayesian model to solve the consistent labeling problem across multiple non-overlapping camera views. Significantly different from related approaches, our model assumes neither people are well segmented nor their trajectories across camera views are estimated. We formulate a spatial-temporal probabilistic model in the hypothesis space that consists the potentially matched objects between the exit field of view (FOV) of one camera and the entry FOV of another camera. A competitive major color spectrum histogram representation (CMCSHR) for appearance matching between two objects is also proposed. The proposed spatial-temporal and appearance models are unified by a maximum-a-posteriori (MAP) Bayesian model. Based on this Bayesian model, when a detected new object corresponds to a group hypothesis (more than one object), we further develop an online method for online correspondence update using optimal graph matching (OGM) algorithm. Experimental results on three different real scenarios validate the proposed Bayesian model approach and the CMCSHR method. The results also show that the proposed approach is able to address the occlusion problem/group problem, i.e. finding the corresponding individuals in another camera view for a group of people who walk together into the entry FOV of a camera.     

Solving the Shallow Water equations using 2D SPH particles for interactive applications

In this paper, we introduce a 2D particle-based approach to achieve realistic water surface behaviors for interactive applications. We formulate 2D particle-based Shallow Water equations using the Smoothed Particle Hydrodynamics. Particles defined with specific amount of water volume interplay with each other, which generates the horizon flow and the water surface motion. By the application of the particle-based Lagrangian framework to the 2D Shallow Water simulation, our method allows the water particles to move freely without being confined to a grid. The motion of the particles can represent global flow with dynamic waves covering a large area while avoiding extensive 3D fluid dynamics computation. The 2D particle-based Shallow Water equations are straightforward and computed fast with the GPU-based implementation. Experiments on a standard hardware demonstrate the performance of our approach which is running on the GPU, and the results show a realistic motion of the water surface at interactive rates.     

Chan-Vese模型下的脑肿瘤图像分割方法

提出了一种基于Chan-Vese模型的脑肿瘤图像分割与三维重构方法。该方法首先通过对脑肿瘤图片的迭代腐蚀操作提取脑肿瘤轮廓,然后利用Chan-Vese模型对脑肿瘤进行分割,最后对图像进行迭代膨胀操作复原图像。另外对所有分割后的脑肿瘤图片进行了三维重构与定位。实验结果表明,基于Chan-Vese模型的图像分割方法很好地解决了脑肿瘤分割过程中容易出现的不完全分割问题,同时对脑肿瘤的三维重构与定位也具有较大的临床实用价值。     

Direct manipulations of B-spline and NURBS curves

This paper presents a method for the direct manipulations of B-spline and non-uniform rational B-splines (NURBS) curves using geometric constraints. A deformable model is developed to define the deformation energy functional of B-spline and NURBS curves. The finite element method is used to minimize the deformation energy functional and solve for the deformed shape of curves subjected to constraints. This approach results in a set of linear equations for a B-spline curve and a set of non-linear equations for a NURBS curve. A perspective mapping is used to linearize the NURBS formulations. NURBS curves are first mapped from the 3D Cartesian coordinate space to the 4D homogeneous coordinate space, and transformed to 4D B-spline curves. After the manipulation in the 4D homogeneous coordinate space, the modified NURBS curves are then mapped back to the 3D Cartesian coordinate space. The approach is implemented by a prototype program, which is written in C, and runs under WINDOWS. Several examples are presented to demonstrate the capabilities of this approach.     

Constructing a 3D trunk model from two images

Trees stand for a key component in the natural environment, thus modeling realistic trees has received much attentions of researchers in computer graphics. However, most trees in computer graphics are generated according to some procedural rules in conjunction with some random perturbations, thus they are generally different from the real trees in the natural environment. In this paper, we propose a systematic approach to create a 3D trunk graphical model from two images so that the created trunk has a similar 3D trunk structure to the real one. In the proposed system, the trunk is first segmented from the image via an interactive segmentation tool and its skeleton is then extracted. Some points on the skeleton are selected and their context relations are established for representing the 2D trunk structure. A camera self-calibration algorithm appropriate for the two-view case is developed, and a minimum curvature constraint is employed to recover the 3D trunk skeleton from the established 2D trunk structure and the calibrated camera. The trunk is then modeled by a set of generalized cylinders around the recovered 3D trunk skeleton. A polygonal mesh representing the trunk is finally generated and a textured 3D trunk model is also produced by mapping the image onto the surface of the 3D trunk model. We have conducted some experiments and the results demonstrated that the proposed system can actually yield a visually plausible 3D trunk model which is similar to the real one in the image.     

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.     

基于CV／CAD的三维物体几何建模

在虚拟现实等技术领域中,都涉及到由现实世界中的实际景物建立对应的计算机描述的虚拟景物的问题,为此提出了利用计算机视觉与CAD几何建模技术相结合的三维珠体建模途径,首先通过编码光栅方法获取三维物体的深度图象,并采用数学形态学的方法加以分割,然后利用代数曲面拟合手段对分割后的三维曲面片进行重建,并使用CAD几何建模工具由重建的曲面片构成物体的几何模型,该文给出了初步的实验结果,证明所提出的技术途径基本可行。     

一种图像纹理分割的小波-像素曲线演化方法

提出了图像纹理分割的小波—曲线演化方法，该方法运用二维小波对纹理图像进行分解，由四个小波系数描述纹理特征，并组成四维小波系数特征矢量图，然后采用最大后验概率模型的曲线演化方法，对特征矢量图进行分割和分类，从而获得原图像纹理分割结果．实验结果表明，与小波—FCM聚类纹理分割方法相比，该方法对双纹理图像能取得较好的分割效果，分割出的边界连续，并且具有较强的抗噪能力．     

Model-driven segmentation of articulating humans in Laplacian Eigenspace

We propose a general approach using Laplacian Eigenmaps and a graphical model of the human body to segment 3D voxel data of humans into different articulated chains. In the bottom-up stage, the voxels are transformed into a high-dimensional (6D or less) Laplacian Eigenspace (LE) of the voxel neighborhood graph. We show that LE is effective at mapping voxels on long articulated chains to nodes on smooth 1D curves that can be easily discriminated, and prove these properties using representative graphs. We fit 1D splines to voxels belonging to different articulated chains such as the limbs, head and trunk, and determine the boundary between splines using the spline fitting error. A top-down probabilistic approach is then used to register the segmented chains, utilizing their mutual connectivity and individual properties. Our approach enables us to deal with complex poses such as those where the limbs form loops. We use the segmentation results to automatically estimate the human body models. While we use human subjects in our experiments, the method is fairly general and can be applied to voxel-based segmentation of any articulated object composed of long chains. We present results on real and synthetic data that illustrate the usefulness of this approach.     

基于区域增长与局部自适应C-V模型的脑血管分割

提出了一种针对TOF MRA(time-of-flight magnetic resonance angiography)磁共振图像的双重分割脑血管提取方法。首先结合高斯滤波,采用二维OTSU算法,结合MIP(maximum intensity projection)图像获得三维血管种子点,定义全局与局部信息相结合的区域增长规则,通过区域增长算法对血管进行粗分割;然后,采用 Catt 扩散模型对体数据场进行各向异性滤波,提出了局部自适应C-V模型,将初步分割结果作为自适应活动轮廓模型的初始轮廓线进行二次分割。实验结果表明,该算法不仅能够有效分割脑血管粗大分支,而且还能精确提取脑血管的细小结构。     

高速公路匝道非线性反馈控制器的设计与仿真

提出了一种非线性方法设计高速公路入口匝道反馈控制器,非线性反馈控制器由高速公路交通流模型和比例积分调节器组成。阐述了入口匝道控制原理,建立了高速公路交通流模型,模型的流量—密度关系是非线性的,设计了高速公路匝道非线性反馈控制器模型。仿真结果表明非线性反馈控制器性能优越,它能使高速公路主线交通流密度保持为设定的期望密度,同时又能维持可接受的匝道服务水平。     

基于散射模型的水下图像复原

水下图像的衰减度与成像距离有直接关系．为了在没有精确深度图情况下有效恢复水下图像,提出基 于散射模型的分段映射方法．研究了水下光线的散射模型,探讨了水下图像的衰减规律;利用水池试验数据采用直 线拟合法建立散射模型;提出基于散射模型的分段映射法．为避免求解精确深度图,利用映射约束条件及少量先验 信息导出多级离散深度值,从而构建出从退化图像到真实图像的分段映射函数．恢复结果表明,所提方法增加了图 像整体对比度,突出了图像细节,明显提高了图像质量．     

Simple Reconstruction of Tree Branches from a Single Range Image

3D modeling of trees in real environments is a challenge in computer graphics and computer vision, since the geometric shape and topological structure of trees are more complex than conventional artificial objects. In this paper, we present a multi-process approach that is mainly performed in 2D space to faithfully construct a 3D model of the trunk and main branches of a real tree from a single range image. The range image is first segmented into patches by jump edge detection based on depth discontinuity. Coarse skeleton points and initial radii are then computed from the contour of each patch. Axis directions are estimated using cylinder fitting in the neighborhood of each coarse skeleton point. With the help of axis directions, skeleton nodes and corresponding radii are computed. Finally, these skeleton nodes are hierarchically connected, and improper radii are modified based on plant knowledge. 3D models generated from single range images of real trees demonstrate the effectiveness of our method. The main contributions of this paper are simple reconstruction by virtue of image storage order of single scan and skeleton computation based on axis directions.     

Analytical development of dynamic equations of motion for a three-dimensional flexible link manipulator with revolute and prismatic joints

In this paper, a mathematical model capable of handling a three-dimensional (3D) flexible n-degree of freedom manipulator having both revolute and prismatic joints is considered. This model is used to study the longitudinal, transversal, and torsional vibration characteristics of the robot manipulator and obtain kinematic and dynamic equations of motion. The presence of prismatic joints makes the mathematical derivation complex. In this paper, for the first time, prismatic joints as well as revolute joints have been considered in the structure of a 3D flexible n-degree of freedom manipulator. The kinematic and dynamic equations of motion representing longitudinal, transversal, and torsional vibration characteristics have been solved in parametric form with no discretization. In this investigation, in order to obtain an analytical solution of the vibrational equations, a novel approach is presented using the perturbation method. By solving the equations of motion, it is shown that mode shapes of the link with prismatic joints can be modeled as the equivalent clamped beam at each time instant. As an example, this method is applied to a three degrees of freedom robot with revolute and prismatic joints. The obtained equations are solved using the perturbation method and the results are used to simulate vibrational behavior of the manipulator.     

Shape representation using a generalized potential field model

This paper is concerned with efficient derivation of the medial axis transform of a 2D polygonal region. Instead of using the shortest distance to the region border, a potential field model is used for computational efficiency. The region border is assumed to be charged and the valleys of the resulting potential field are used to estimate the axes for the medial axis transform. The potential valleys are found by following the force field, thus, avoiding 2D search. The potential field is computed in closed form using equations of the border segments. The simple Newtonian potential is shown to be inadequate for this purpose. A higher order potential is defined which decays faster with distance than the inverse of distance. It is shown that as the potential order becomes arbitrarily large, the axes approach those computed using the shortest distance to the border. Algorithms are given for the computation of axes, which can run in linear parallel time for part of the axes having initial guesses. Experimental results are presented for a number of examples