Constraints on length and angle

Given a perspective projection of line segments on the image plane, the constraints on their 3D positions and orientations are derived on the assumption that their true lengths or the true angles they make are known. The approach here is first to transform images of line segments to the center of the image plane as if the camera were rotated to aim at them. The 3D information extracted in this canonical position is then transformed back to the original configuration. Examples are given, by using real images, for analytical 3D recovery of a rectangular corner and a corner with two right angles.     

Affine transformations for digitized spatial data in geology

Affine transformations are among the most basic and useful geometrical operations in computer applications in geology. Homogeneous coordinates extend their applicability. The methods are essential in handling digitized locational data and are applicable widely in other graphical applications such as calibrating data sets for plotting, and in shape comparison and spatial analysis. Affine transformations alter the length of lines and the angles between them, whereas straight lines remain straight, parallel lines remain parallel, and the ratio in which a point divides a line remains the same.Their geometrical significance indicates that they can be visualized readily, and the corresponding operations in matrix algebra provide a straightforward method of computer implementation. A transformation matrix is calculated from four calibration points, the coordinates of which are known before and after transformation. Multiplication of coordinates in the initial frame of reference by the transformation matrix converts them to coordinates in the new frame of reference. A listing of relevant FORTRAN programs is given, with examples.     

Convex Relaxation of a Class of Vertex Penalizing Functionals

We investigate a class of variational problems that incorporate in some sense curvature information of the level lines. The functionals we consider incorporate metrics defined on the orientations of pairs of line segments that meet in the vertices of the level lines. We discuss two particular instances: One instance that minimizes the total number of vertices of the level lines and another instance that minimizes the total sum of the absolute exterior angles between the line segments. In case of smooth level lines, the latter corresponds to the total absolute curvature. We show that these problems can be solved approximately by means of a tractable convex relaxation in higher dimensions. In our numerical experiments we present preliminary results for image segmentation, image denoising and image inpainting.     

Extraction of power-transmission lines from vehicle-borne lidar data

This paper presents a step-wise method for extracting power-transmission lines and towers from vehicle-borne light detection and ranging (lidar) data. First, this method estimates road ranges with regard to incidence angles and separates off-road points from road-surface points by applying elevation-difference and slope criteria to the road ranges scan-line by scan-line. Then, three filters, in terms of height, spatial density, and a combination of size and shape, are proposed to extract power-transmission line/power tower points from the identified off-road points, followed by the extraction of individual power-transmission lines via Hough transform and Euclidean distance clustering. Finally, a three-dimensional (3D) power-transmission line is modelled as a horizontal line in the x–y plane and a vertical catenary curve defined by a hyperbolic cosine function in the x–z plane. We evaluated the method using two data sets acquired by the RIEGL VMX-450 system. The average completeness, correctness, and quality of the extracted power-lines on two data sets are 0.92, 0.99, and 0.91, respectively, and the positional accuracies including root mean square error and maximum error averaged 0.07 and 0.05 m, respectively. The results show that the proposed method extracts power-transmission lines from large-scale, vehicle-borne lidar data with good thematic and positional accuracy.     

基于直线约束的非量测数码相机标定

提出一种非量测数码相机标定的直接方法。该方法基于直线约束条件,即在正确进行畸变纠正后,物方空间的三维直线投影到像片平面上也应该是一条直线。为了将畸变直线纠正成理想直线,利用畸变模型对其进行畸变纠正,并采用Levenberg-Marquardt算法对非线性方程组进行求解,解出符合条件的最佳畸变参数。实验结果证明该方法具有较强的鲁棒性与实用性。     

Camera calibration by vanishing lines for 3-D computer vision

A novel approach to camera calibration by vanishing lines is proposed. Calibrated parameters include the orientation, position, and focal length of a camera. A hexagon is used as the calibration target to generate a vanishing line of the ground plane from its projected image. It is shown that the vanishing line includes useful geometric hints about the camera orientation parameters and the focal length, from which the orientation parameters can be solved easily and analytically. And the camera position parameters can be calibrated by the use of related geometric projective relationships. The simplicity of the target eliminates the complexity of the environment setup and simplifies the feature extraction in relevant image processing. The calibration formulas are also simple to compute. Experimental results show the feasibility of the proposed approach     

线结构光扫描传感器结构参数一体化标定

为了精确快捷地标定线结构光扫描传感器的结构参数,提出了一种线结构光扫描传感器结构参数一体化现场标定的新方法,建立了线结构光扫描传感器的数学模型,根据张正友摄像机标定思想结合L-M非线性优化算法能快速精确地完成摄像机内外参数的标定,在此基础上,引入辅助线激光,通过反复多次提取两激光交点完成对线结构光平面精确标定。文章还介绍了如何获取激光交点以及精确提取交点坐标的方法,通过设计相关实验验证了本文方法的可行性,使系统精度优于24μm,能满足实际测量要求。     

An eigenstructure-based 2D DOA estimation method using dual-size spatial invariance array

A sparse planar array vertically placed in y-z plane is proposed to improve the angle estimation accuracy of sources in low angle region with reflection multipath.With two sizes of spatial invariances along both dimensions,the array estimates the azimuth and elevation angles using unitary ESPRIT(estimation of signal parameters via rotational invariance techniques).The first spatial invariance with a displacement of half-wavelength yields unambiguous coarse estimates of high-variance,while the second spatial...     

基于物方几何约束提取建筑物垂直边缘

航空影像中，垂直边缘对建筑物提取具有重要意义。为快速准确地提取垂直边缘，依据航空摄影测量学的有关知识，利用摄影测量成像模型推导出垂直边缘灭点位置，并结合物方空间几何约束和图像空间边缘信息，采用一种自适应模糊Hough变换算法，实现了建筑物垂直边缘的自动提取。实验证明，该算法是行之有效的。     

基于多分割和口袋方法的最小二乘分类算法

提出了一种改进的最小二乘分类算法,该算法首先利用最小二乘算法对两类数据分类,然后计算每类的中心点,过中心点作已得到的分类线(面)的平行线(面),保留所作平行线(面)之间及线(面)上的数据,剔除其余数据,对剩余数据重新利用最小二乘算法分类,如此循环.在循环过程中利用口袋方法记录下具有最好的分类效果的分类线(面),循环结束后口袋中即为最佳分类线(面).实验结果表明,该算法有效的解决了原有最小二乘分类算法的缺陷,有着良好的分类效果.     

Solving the orientation-duality problem for a circular feature inmotion

Circular features have been commonly used in numerous computer vision application areas for 3D pose estimation. However, although the 3D position of the circle's center can be uniquely identified, the solution process yields two different feasible orientations, of which only one is the true solution. In this paper, two methods are presented for the solution of the orientation-duality problem for circular features that are in motion. The first approach is applicable to those features moving on a 3D line with constant orientation or to those which are moving on a plane with general motion. The second approach relies on the existence of additional object features, such as points or lines, which are coplanar to the circular feature. In this case, the circular feature can undergo an arbitrary 3D motion. Experimental results verify the validity of the proposed methods     

Effects of standardized foot positions during the execution of a submaximal pulling task

This study examined how experimentally controlled foot positions could affect the temporal and spatial parameters of a load (20% of subject mass) during a one-handed repetitive submaximal pulling activity. Foot positions standardized relative to a frontal and sagittal plane defining a pull force vector were derived based on the preferences of 45 volunteer subjects. In general, the subjects assumed asymmetrical foot positions and on average the big toe of the foot contralateral to the hand exerting the pull was located 19% (SD = 4.4) of stature in front of the frontal plane containing the pull origin and 8.6% (SD = 4.5) of stature laterally from the sagittal plane through which the load was displaced. The big toe of the foot ipsilateral to the hand exerting the force was located at a distance of 46.7% (SD = 6.3) of stature in front of the frontal plane containing the pull origin and 0.4% (SD = 3.9) of stature laterally from the sagittal plane through which the load was displaced. The left and right feet were orientated at angles of 56.8° (SD = 20.2°) and 25.9° (SD = 22.7°), respectively, relative to a right horizontal of a frontal plane parallel to the plane containing the origin of pull. These foot positions were subsequently employed in a second experiment to investigate how dictating foot positions would affect the way in which 15 newly recruited subjects exerted a pull force on the same load. Results from this experiment showed that the load velocities and forces were not affected by standardized foot positions when compared to those collected when subjects were free to choose foot orientations. It is suggested that future researchers should consider the benefits of employing standardized foot positions in studies of pull exertions, particularly for methodologies similar to that described in this study.     

Effects of standardized foot positions during the execution of a submaximal pulling task

This study examined how experimentally controlled foot positions could affect the temporal and spatial parameters of a load (20% of subject mass) during a one-handed repetitive submaximal pulling activity. Foot positions standardized relative to a frontal and sagittal plane defining a pull force vector were derived based on the preferences of 45 volunteer subjects. In general, the subjects assumed asymmetrical foot positions and on average the big toe of the foot contralateral to the hand exerting the pull was located 19% (SD = 4.4) of stature in front of the frontal plane containing the pull origin and 8.6% (SD = 4.5) of stature laterally from the sagittal plane through which the load was displaced. The big toe of the foot ipsilateral to the hand exerting the force was located at a distance of 46.7% (SD = 6.3) of stature in front of the frontal plane containing the pull origin and 0.4% (SD = 3.9) of stature laterally from the sagittal plane through which the load was displaced. The left and right feet were orientated at angles of 56.8 degrees (SD = 20.2 degrees ) and 25.9 degrees (SD = 22.7 degrees ), respectively, relative to a right horizontal of a frontal plane parallel to the plane containing the origin of pull. These foot positions were subsequently employed in a second experiment to investigate how dictating foot positions would affect the way in which 15 newly recruited subjects exerted a pull force on the same load. Results from this experiment showed that the load velocities and forces were not affected by standardized foot positions when compared to those collected when subjects were free to choose foot orientations. It is suggested that future researchers should consider the benefits of employing standardized foot positions in studies of pull exertions, particularly for methodologies similar to that described in this study.     

Fingerprint classification using a feedback-based line detector

We present a fingerprint classification algorithm in this paper. This algorithm classifies a fingerprint image into one of the five classes: Arch, Left loop, Right loop, Whorl, and Tented arch. We use a new low-dimensional feature vector obtained from the output of a novel oriented line detector presented here. Our line detector is a co-operative dynamical system that gives oriented lines and preserves multiple orientations at points where differently oriented lines meet. Our feature extraction process is based on characterizing the distribution of orientations around the fingerprint. We discuss three different classifiers: support vector machines, nearest-neighbor classifier, and neural network classifier. We present results obtained on a National Institute of Standards and Technology (NIST) fingerprint database and compare with other published results on NIST databases. All our classifiers perform equally well, and this suggests that our novel line detection and feature extraction process indeed captures all the crucial information needed for classification in this problem.     

Crosstalk analysis of multi‐microstrip coupled lines using transmission line modeling

This article presents a new analytical method to predict crosstalk of a homogeneous terminated two microstrip coupled lines over a ground plane using transmission line theory. The derived formula is frequency and location dependent, which can be used to quickly estimate the crosstalk of a coupled line. Also, the effect of the geometrical parameters of the lines and load are included in the derived formula. Presented method can be used for the other types of coupled lines including lossy or lossless lines. To verify the accuracy of the introduced method, a few microstrip coupled line structures with different geometrical parameters are considered numerically and experimentally. The results of crosstalk based on the proposed analytical methods, simulation study using high frequency structure simulator and those obtained by measurements are reported and compared with each other. It is shown that our proposed method accurately estimates the amount of crosstalk for a two microstrip coupled lines.     

Rectifying perspective views of text in 3D scenes using vanishing points

Documents may be captured at any orientation when viewed with a hand-held camera. Here, a method of recovering fronto-parallel views of perspectively skewed text documents in single images is presented, useful for ‘point-and-click’ scanning or when generally seeking regions of text in a scene. We introduce a novel extension to the commonly used 2D projection profiles in document recognition to locate the horizontal vanishing point of the text plane. Following further analysis, we segment the lines of text to determine the style of justification of the paragraphs. The change in line spacings exhibited due to perspective is then used to locate the document's vertical vanishing point. No knowledge of the camera focal length is assumed. Using the vanishing points, a fronto-parallel view is recovered which is then suitable for OCR or other high-level recognition. We provide results demonstrating the algorithm's performance on documents over a wide range of orientations.     

Extracting curved text lines using local linearity of the text line

In order to enhance the ability of document analysis systems, we need a text line extraction method which can handle not only straight text lines but also text lines in various shapes. This paper proposes a new method called Extended Linear Segment Linking (ELSL for short), which is able to extract text lines in arbitrary orientations and curved text lines. We also consider the existence of both horizontally and vertically printed text lines on the same page. The new method can produce text line candidates for multiple orientations. We verify the ability of the method by some experiments as well. Received December 21, 1998 / Revised version September 2, 1999     

Performance evaluation and analysis of vanishing point detectiontechniques

Vanishing point detection algorithms based on a Gaussian sphere representation have been employed in a variety of computer vision systems, for extracting 3D line orientations as a first step towards object detection. Typically, these algorithms have been applied to imagery with strong perspective effects and with little noise or texture, resulting in good solutions for line orientations. However, these algorithms can fail if perspective effects are weak, or if texture edges are predominant; they also fail to take advantage of knowledge about the objects to be detected. In this paper, two new techniques for robust vanishing point detection on the Gaussian sphere are presented; primitive-based vanishing point analysis and interpretation plane error modeling. The performance of these methods, along with two other existing methods from the literature, are quantitatively evaluated and compared for the task of building detection in complex aerial imagery     

A Terrain Rendering Method Using Vertical Ray Coherence

Ray casting may be applied to the terrain rendering from DTMs (digital terrain models). In this paper we propose a ray casting method which exploits exact vertical ray coherence. This method not only achieves a good performance, but also allows any set of viewing parameters. To analyse the vertical ray coherence property, we define the following terms: a ray plane which is perpendicular to the sea-level plane and passes through the COP (centre of projection), and the corresponding ray line which is the line of intersection of the ray plane and the projection plane. Vertical ray coherence can be stated as: if two rays pass through the same ray line, they pass over the identical set of points on the DTM base plane. After a ray is cast on the DTM, we can get a good starting point to cast another ray using this property. Our method tries to cover the projection plane with ray lines. Since ray lines are not parallel to each other, it is a difficult task to cover the entire plane. In fact all ray lines intersect at a point (COP′). We first generate a set of ray lines sufficient to cover the projection plane near COP′. As pixels get further from COP′, more ray lines are generated to fill most of the gaps between pixels covered by the previous set of ray lines. Rays passing through the same ray line are effectively cast using vertical ray coherence. To fill remaining pixels not covered by ray lines, pixel values of vertical/horizontal neighbours are interpolated. To cast rays efficiently, successive points generated by a line algorithm are followed along the projection of the rays on the DTM base plane. © 1997 by John Wiley & Sons, Ltd.