Uncalibrated reconstruction: an adaptation to structured light vision

Euclidean reconstruction from two uncalibrated stereoscopic views is achievable from the knowledge of geometrical constraints about the environment. Unfortunately, these constraints may be quite difficult to obtain. In this paper, we propose an approach based on structured lighting, which has the advantage of providing geometrical constraints independent of the scene geometry. Moreover, the use of structured light provides a unique solution to the tricky correspondence problem present in stereovision. The projection matrices are first computed by using a canonical representation, and a projective reconstruction is performed. Then, several constraints are generated from the image analysis and the projective reconstruction is upgraded into an Euclidean one—as we will demonstrate, it is assumed that the sensor behaviour is affine without loss of generality so that the constraints generation is simplified. The method provides our sensor with adaptive capabilities and permits to be used in the measurement of moving scenes such as dynamic visual inspection or mobile robot navigation. Experimental results obtained from both simulated and real data are presented.     

Self-recalibration of a structured light system via plane-based homography

Self-recalibration of the relative pose in a vision system plays a very important role in many applications and much research has been conducted on this issue over the years. However, most existing methods require information of some points in general three-dimensional positions for the calibration, which is hard to be met in many practical applications. In this paper, we present a new method for the self-recalibration of a structured light system by a single image in the presence of a planar surface in the scene. Assuming that the intrinsic parameters of the camera and the projector are known from initial calibration, we show that their relative position and orientation can be determined automatically from four projection correspondences between an image and a projection plane. In this method, analytical solutions are obtained from second order equations with a single variable and the optimization process is very fast. Another advantage is the enhanced robustness in implementation via the use of over constrained systems. Computer simulations and real data experiments are carried out to validate our method.     

3-D shape reconstruction in an active stereo vision system using genetic algorithms

The recovery of 3-D shape information (depth) using stereo vision analysis is one of the major areas in computer vision and has given rise to a great deal of literature in the recent past. The widely known stereo vision methods are the passive stereo vision approaches that use two cameras. Obtaining 3-D information involves the identification of the corresponding 2-D points between left and right images. Most existing methods tackle this matching task from singular points, i.e. finding points in both image planes with more or less the same neighborhood characteristics. One key problem we have to solve is that we are on the first instance unable to know a priori whether a point in the first image has a correspondence or not due to surface occlusion or simply because it has been projected out of the scope of the second camera. This makes the matching process very difficult and imposes a need of an a posteriori stage to remove false matching.In this paper we are concerned with the active stereo vision systems which offer an alternative to the passive stereo vision systems. In our system, a light projector that illuminates objects to be analyzed by a pyramid-shaped laser beam replaces one of the two cameras. The projections of laser rays on the objects are detected as spots in the image. In this particular case, only one image needs to be treated, and the stereo matching problem boils down to associating the laser rays and their corresponding real spots in the 2-D image. We have expressed this problem as a minimization of a global function that we propose to perform using Genetic Algorithms (GAs). We have implemented two different algorithms: in the first, GAs are performed after a deterministic search. In the second, data is partitioned into clusters and GAs are independently applied in each cluster. In our second contribution in this paper, we have described an efficient system calibration method. Experimental results are presented to illustrate the feasibility of our approach. The proposed method yields high accuracy 3-D reconstruction even for complex objects. We conclude that GAs can effectively be applied to this matching problem.     

A state of the art in structured light patterns for surface profilometry

Shape reconstruction using coded structured light is considered one of the most reliable techniques to recover object surfaces. Having a calibrated projector-camera pair, a light pattern is projected onto the scene and imaged by the camera. Correspondences between projected and recovered patterns are found and used to extract 3D surface information. This paper presents an up-to-date review and a new classification of the existing techniques. Some of these techniques have been implemented and compared, obtaining both qualitative and quantitative results. The advantages and drawbacks of the different patterns and their potentials are discussed.     

A graph-theoretic characterization for the rank of the transfer matrix of a structured system

In this paper structured systems are considered and the generic rank of the transfer matrix of such systems is introduced. It is shown that this rank equals the maximum number of vertex disjoint paths from the input vertices to the output vertices in the graph that can be associated to the structured system. This maximum number of disjoint paths can be calculated using techniques from combinatorics. As an application a structural version of the well-known almost disturbance decoupling problem is proposed. The results in this paper were obtained while the author was affiliated with the Centre for Mathematics and Computer Science in Amsterdam, The Netherlands.     

Efficient multiple phase shift patterns for dense 3D acquisition in structured light scanning

Although phase shifts (PS) are frequently used to acquire colored surfaces of static objects, especially when acquisition time is not critical, the periodic nature of relative (wrapped) PS maps makes it necessary to deal with the issue of phase unwrapping. Consequently, multiple phase shifts (MPS) have been widely used as an alternative, but this usually involves a large number of different PS maps to unwrap an absolute (unique) phase. In this paper we propose a new MPS method to unwrap a phase and accurately perform the dense 3D acquisition of neutral and colored objects using only two PS maps. Accuracy is reported including a quantitative and qualitative evaluation of the results.     

Towards a real-time 3D shape reconstruction using a structured light system

This paper deals with 3D shape reconstruction using a structured light system (SLS) which projects a matrix of laser rays onto the scene to be analyzed. The intrinsic problem of such a system is the correspondence problem solving, which in this particular case amounts to matching up the imaged spots and the originating laser rays. In this paper, we propose a method for automatically obtaining configurations of the system (COS) (i.e. the relative positions of the camera, laser projector, and measuring scene) that permit to achieve a direct and unambiguous correspondence. After, we propose a splitting cell algorithm, which efficiently performs a real-time correspondence procedure. Experimental results obtained from both simulated and real data demonstrate that our method provides our SLS with possibilities for real-time applications.     

Fast acquisition of dense depth data by a new structured light scheme

This paper introduces a new structured lighting scheme to obtain dense depth data fast and reliably. Its main idea is to use both features and continuous intensities organized in a hierarchical structure as the projection pattern. This hierarchical structure then guides the matching process. As a result, a dense depth map can be reliably acquired by grabbing only one image (or two images for better precision). Experimental results using a prototype system with two cameras and a lighting projector show that the proposed scheme is effective and efficient.     

基于结构光视觉的白车身覆盖件间隙面差测量方法

针对白车身表面覆盖件间隙面差人工测量精度差、效率低等问题,提出了利用结构光视觉测量方法代替人工测量.在间隙特征点识别中,计算光纹中心线上各点的绝对差分值,搜索差分极值点并将该极值点作为特征点;在面差特征点识别中,采用基于离散曲线曲率极值点的特征点定位算法.实验结果表明:间隙面差测量方法测量精度较高,能够满足整车厂对白车身间隙面差测量精度的要求.     

Machine vision system for curved surface inspection

This application-oriented paper discusses a non-contact 3D range data measurement system to improve the performance of the existing 2D herring roe grading system. The existing system uses a single CCD camera with unstructured halogen lighting to acquire and analyze the shape of the 2D shape of the herring roe for size and deformity grading. Our system will act as an additional system module, which can be integrated into the existing 2D grading system, providing the additional third dimension to detect deformities in the herring roe, which were not detected in the 2D analysis. Furthermore, the additional surface depth data will increase the accuracy of the weight information used in the existing grading system. In the proposed system, multiple laser light stripes are projected into the herring roe and the single B/W CCD camera records the image of the scene. The distortion in the projected line pattern is due to the surface curvature and orientation. Utilizing the linear relation between the projected line distortion and surface depth, the range data was recovered from a single camera image. The measurement technique is described and the depth information is obtained through four steps: (1) image capture, (2) stripe extraction, (3) stripe coding, (4) triangulation, and system calibration. Then, this depth information can be converted into the curvature and orientation of the shape for deformity inspection, and also used for the weight estimation. Preliminary results are included to show the feasibility and performance of our measurement technique. The accuracy and reliability of the computerized herring roe grading system can be greatly improved by integrating this system into existing system in the future.     

一种月球车的环境重建方法

根据对月球车双目立体视觉系统及其工作环境的分析,提出了一种基于相机离线标定和区域生长的稠密匹配相结合的月球车环境重建方法,通过相机离线标定、极线校正和基于区域生长的立体匹配,得到月球车漫游环境的重构地图;首先,与常用的相机标定方法相比,基于OpenCV的相机离线标定在得到可靠的相机参数的同时,减少了三维重建的时间,提高了实时性;其次,通过极线校正和改进的区域生长立体匹配方法可以快速的得到稠密的月球车的环境深度图;实验结果证明了该方法的有效性。     

A theoretical investigation of the emerging standards for web services

Currently, standards for web services are being developed via three different initiatives (W3C, Semantic web services and ebXML). To the best of our knowledge, no theoretical perspectives underlie these standardization efforts. Without the benefit of a strong theoretical basis, the results, within and across these initiatives, have remained piecemeal. We suggest ‘Language–Action Theories’ as a plausible perspective that can effectively define, assess and refine web services standards. In this paper, we first investigate the existing initiatives to identify commonalities that point to theories of ‘Language–Action’ as an appropriate theoretical basis for web services standards. Next, we adapt work from these theories to develop a comprehensive reference framework for understanding web services standards. Finally, we use this reference framework to assess the three initiatives, and analyze the findings to provide insights for future development and refinement of web services standards.

A stereo-vision system for support of planetary surface exploration

Abstract. In this paper, we present a system that was developed for the European Space Agency (ESA) for the support of planetary exploration. The system that is sent to the planetary surface consists of a rover and a lander. The lander contains a stereo head equipped with a pan-tilt mechanism. This vision system is used both for modeling the terrain and for localization of the rover. Both tasks are necessary for the navigation of the rover. Due to the stress that occurs during the flight, a recalibration of the stereo-vision system is required once it is deployed on the planet. Practical limitations make it unfeasible to use a known calibration pattern for this purpose; therefore, a new calibration procedure had to be developed that could work on images of the planetary environment. This automatic procedure recovers the relative orientation of the cameras and the pan and tilt axes, as well as the exterior orientation for all the images. The same images are subsequently used to reconstruct the 3-D structure of the terrain. For this purpose, a dense stereo-matching algorithm is used that (after rectification) computes a disparity map. Finally, all the disparity maps are merged into a single digital terrain model. In this paper, a simple and elegant procedure is proposed that achieves that goal. The fact that the same images can be used for both calibration and 3-D reconstruction is important, since, in general, the communication bandwidth is very limited. In addition to navigation and path planning, the 3-D model of the terrain is also used for virtual-reality simulations of the mission, wherein the model is texture mapped with the original images. The system has been implemented, and the first tests on the ESA planetary terrain testbed were successful.     

Lyapunov controller design for transverse vibration of a cable-linked transporter system

Modeling and Lyapunov controller design for transverse vibration of a flexible cable transporter system with arbitrarily varying lengths are presented using Hamilton's principle and Lyapunov theory. The axial velocity of the system is assumed to be unknown in the model. This is different from existing literature where the axial velocity is assumed either to be constant or prescribed. The governing equations include two coupled non-linear Partial Differential Equations (PDEs) and boundary conditions. The interactions between the cables and the slider, pulleys, and motors are included in the model. Numerical solution of the derived governing equations is obtained using Galerkin's method. Based on the Lyapunov theory, we propose two boundary controllers and one domain point-wise controller, which suppress the transverse vibration of the cables effectively while assuring the attainment of the slider goal. The proposed controllers dissipate the vibration energy and guarantee the stability of the closed-loop system in Lyapunov sense. Simulation results demonstrate the effectiveness of the proposed controllers.A short version of this paper was presented in 2004 ASME International Mechanical Engineering Conference and Exposition, Anaheim CA, November 14-19, 2004.     

A top-down strategy to reverse architecting execution views for a large and complex software-intensive system: An experience report

This article is an experience report about the application of a top-down strategy to use and embed an architecture reconstruction approach in the incremental software development process of the Philips MRI scanner, a representative large and complex software-intensive system. The approach is an iterative process to construct execution views without being overwhelmed by the system size and complexity. An execution view contains architectural information that describes what the software of a software-intensive system does at runtime and how it does this. The application of the strategy is illustrated with a case study, the construction of an up-to-date execution view for the start-up process of the Philips MRI scanner. The construction of this view helped the development organization to quickly reduce about 30% the start-up time of the scanner, and set up a new system benchmark for assuring the system performance through future evolution steps. The report provides detailed information about the application of the top-down strategy, including how it supports top-down analysis, communication within the development organization, and the aspects that influence the use of the top-down strategy in other contexts.     

Achieving e-Manufacturing: multihead control and web technology for the implementation of a manufacturing execution system

Intelligent Manufacturing Systems requires advanced and efficient manufacturing technologies, management and procedures in order to achieve value creation in global markets. E-Manufacturing is the set of information technologies that allows companies to achieve on demand manufacturing through the integration of e-business applications. Cornerstone of this concept are Demand Flow Technology, Manufacturing Execution Systems (MES) and Digital Operational Method Sheets (OMS) which are vital to control shop floor operations where there is a need to balance manual and automated operations. Specially, Mexican companies face large diversity of products and multiple production lines, with high turnaround rotation of the workers. A low cost solution that integrates Demand Flow Technology, MES with Digital OMS is described, the system has been developed using LINUX servers, Multi-head control technology (multiple monitors to a single server) and a WEB based environment. This technological solution offers an affordable, stable, and high performance solution to transform the production into a more balanced system with shorter and faster cycles allowing a company to achieve e-Manufacturing. Received: February 2005/Accepted: January 2006     

Industrial application of machine-in-the-loop-learning for a medical robot vision system - Concept and comprehensive field study

The availability of increasingly powerful sensors and processing hardware provides the means for performing more and more complex signal processing and recognition tasks. In particular, vision systems have been the subject of intensive research and successful application during the last two decades, whereby they have often been augmented by auxiliary sensors. However, several fundamental challenges concerning the design and application of such systems remain. From the plethora of off-the-shelf-hardware, sensors and algorithms which is available a selection must be made which results in a feasible and well performing system which at the same time is capable of meeting constraints such as cost and power consumption, for instance. Currently, the design process is undergoing a paradigm shift from expert driven to automated design. Learning and optimisation techniques have proved to be more than able to compete with expert based solutions in many cases. As soon as a developed solution is deployed to more than one installation site and operated for an extended period of time under significantly varying environmental conditions, the initial solution will no longer be applicable and adjustment or fine-tuning will be required. This paper presents a conceptual solution to this challenge for the application of a medical robot vision system for the task of tube type detection. Laboratories employ this robot system for semi-automated or automated analysis of medical samples at numerous sites. The varying environmental conditions and variations in the classification task from situation to situation require reconfiguration capabilities. In our approach, these capabilities are realised in the form of a holistic training concept, designated as machine-in-the-loop-learning (MILL). The current state of concept implementation in the robot vision system with MILL support has allowed for its successful implementation in more than 250 machines at 150 sites worldwide with more than 5000 classifications per day and machine. An error rate of 0.06% was reported in a long-term study of three months duration involving two representative installations. Future work will focus on the refinement of the system architecture and incorporation of recent advances in optimisation, e.g., particle swarm optimisation (PSO) and related methods.