Coordinates Of Points In Space Research Articles

APPLICATION OF LASER SCANNING IN THE BASIC GEODETIC WORKS DURING THE RECONSTRUCTION OF THE THERMAL SPA GUBER COMPLEX

<p class="ABSTRACT">Laser scanning is one of the most modern technologies used for the mass collection of spatial data in the form of coordinates of points in space. Given that laser scanning is often used during the restoration of buildings and building facades, the paper describes the application of mobile laser scanning in the example of the reconstruction of the Banje Guber complex. In the practical part of the work, the cloud of points obtained by scanning the Banja Guber complex was processed and the computer software used for data processing was presented. A 3D model of the terrain and the classic geodetic situation of the Banja Guber complex was created.</p>

Stereo vision based robot welding

The most important advantages of robotic welding are precision and productivity. Introducing visual systems in welding allows one to easily position the elements that are welded. The robot will then perform welding without error after recording the welding points. The application of visual systems in robotics is very important because it enables the autonomous work of the robot. Stereo vision is used for three-dimensional reconstruction of the robot’s environment based on images captured by cameras. The stereo system consists of two cameras and a computer that processes the recorded images using appropriate programs and algorithms. The accuracy of estimating coordinates in space using a visual system is very important, it is necessary to estimate the parameters of the cameras and define their dependence. The relationship between the two cameras, as well as their basic parameters, are assessed by camera calibration. After calibrating the camera for each 2D coordinate, obtained from the camera sensor, it is possible to determine which set of points it belongs to in the 3D coordinate system. One of the most important and most difficult problems in the reconstruction of a 3D object is finding points on the planes of images that were created from the same physical point. The problem of correspondent points is also considered in this paper. To present the efficiency and reliability of the proposed solution for obtaining 3D coordinates of points in space, the proposed solution was tested in the laboratory and satisfactory results are obtained.

Kinematic modeling and error parameter identification of automated fiber placement machine based on measured data

This paper presents a novel kinematic modeling and error parameter identification method for a six-axis gantry automated fiber placement (AFP) machine. Multi-body system theory is used to model the kinematics of the AFP machine, and then use the homogeneous transformation matrix to represent the transfer relationship of the coordinate system. Based on 54 geometric errors of the AFP machine, a volumetric error transfer model is established. To eliminate the training bias caused by sampling randomness, 10-fold cross-validation combined with the Levenberg–Marquardt method is used to train the kinematic model of the AFP machine. Based on the coordinates of random points in space measured by a laser tracker, all the position-dependent geometric errors and position-independent geometric errors of the linear and rotary axes can be identified simultaneously. After the error parameters are identified, the average error of the random points in the X-direction is reduced from 0.72 to 0.08 mm, a drop of 88.9%. Corresponding experiments are carried out on the body diagonals and the winglet placement path. The experimental results show that the volumetric error transfer model and error parameter identification method proposed in the article can accurately predict the volumetric errors of the AFP machine, and can also meet the requirements of the AFP machine placement accuracy.

Prediction of three-dimensional coordinate measurement of space points based on BP neural network

In order to improve the measurement accuracy of three-dimensional coordinate measurement system based on dual-PSD, this paper proposes a three-dimensional coordinate measurement method based on back propagation (BP) neural network considering the high ability of the neural network to deal with the complex nonlinear mapping problem. This method can describe the mapping relationship between three-dimensional coordinates of space points in the world coordinate system and coordinates of light spots on dual-PSD well. Levenberg-Marquardt learning algorithm is used to train the network, and then trained BP neural network model is used to predict three-dimensional coordinates of space points. Experimental results show that the average measurement error of space points obtained by the method is low. It proves that the built BP neural network model can be used to predict three-dimensional coordinates of space points. [Submitted 9 July 2018; Accepted 30 October 2018]

Passive vision measurement for robust reconstruction of molten pool in wire and arc additive manufacturing

Robust measurement of molten pool in wire and arc additive manufacturing can help better understand the geometrical size of fabricated parts and even offer feedback to control this process. Most of existing detection methods are not sufficient to express full geometric features of molten pool. In this paper, a novel passive vision sensing system using a single camera is designed based on the refraction principle of a biprism. Intrinsic and external parameters of left-right virtual cameras and their relative position are solved through a planar pattern, and an image pair is rectified by transmission projection. A global-based iterative matching algorithm is optimized for calculating the left-right parallax images of the image pair, and coordinates of space points are calculated via the triangle measuring method. The proposed sensing system and algorithms are validated by a standard cylinder. The results show that the width error of the calculated cylinder appearance is approximately 3.02% and the maximum height error is 4.15%. Finally, molten pool geometry in gas metal arc (GMA) additive manufacturing is restructured, proving the effectiveness of the virtual binocular vision system and the accuracy of the reconstruction algorithms.

A multilateral laser-tracking three-dimensional coordinate measuring system based on plane constraint

In a multilateral laser-tracking three-dimensional (3D) coordinate measuring system, the error caused by the laser tracker angle measurement is not an issue, while the 3D coordinates of space points are determined using only distance measurement data. Thus in order to improve the accuracy of the whole system it is crucial to calibrate the parameters of the multilateral system with precision. To this end, a parameter-calculating method based on plane constraint is proposed in this paper. A standard plane constraint is used to provide optimal system equations without increasing the number of unknowns. Moreover, while a traditional multilateral system requires at least four stations of laser-tracking measurement, a system based on plane constraint produces more equations, reducing the number of required stations to three. A method for obtaining the required standard plane at the measurement site is also presented in this paper, thus making the above-mentioned scheme feasible. In order to highlight the advantages of a multilateral system over a long distance, an experiment is set up where three scale bars are placed within the range of 25–38 m. The experiment shows that the measurement error of scale bars using a four-station plane constraint model is distributed within the range from 10 to 49 µm, with an average value of 29 µm, while the error using the three-station model is distributed within the range from 31 to 55 µm, with an average value of 39 µm. Using traditional four-station multilateral method the error is distributed from 33 to 79 µm, with an average of 56 µm. The accuracy of the system based on plane constraint appears to be improved compared with single-station measurement and traditional multilateral systems.

Three-dimensional coordinate measurement algorithm by optimizing BP neural network based on GA

PurposeThe purpose of this paper is to solve the problem that the analytic solution model of spatial three-dimensional coordinate measuring system based on dual-position sensitive detector (PSD) is complex and its precision is not high.Design/methodology/approachA new three-dimensional coordinate measurement algorithm by optimizing back propagation (BP) neural network based on genetic algorithm (GA) is proposed. The mapping relation between three-dimensional coordinates of space points in the world coordinate system and light spot coordinates formed on dual-PSD has been built and applied to the prediction of three-dimensional coordinates of space points.FindingsThe average measurement error of three-dimensional coordinates of space points at three-dimensional coordinate measuring system based on dual-PSD based on GA-BP neural network is relatively small. This method does not require considering the lens distortion and the non-linearity of PSD. It has simple structure and high precision and is suitable for three-dimensional coordinate measurement of space points.Originality/valueA new three-dimensional coordinate measurement algorithm by optimizing BP neural network based on GA is proposed to predict three-dimensional coordinates of space points formed on three-dimensional coordinate measuring system based on dual-PSD.

Zoom lens calibration with zoom- and focus-related intrinsic parameters applied to bundle adjustment

A zoom lens is more flexible for photogrammetric measurements under diverse environments than a fixed lens. However, challenges in calibration of zoom-lens cameras preclude the wide use of zoom lenses in the field of close-range photogrammetry. Thus, a novel zoom lens calibration method is proposed in this study. In this method, instead of conducting modeling after monofocal calibrations, we summarize the empirical zoom/focus models of intrinsic parameters first and then incorporate these parameters into traditional collinearity equations to construct the fundamental mathematical model, i.e., collinearity equations with zoom- and focus-related intrinsic parameters. Similar to monofocal calibration, images taken at several combinations of zoom and focus settings are processed in a single self-calibration bundle adjustment. In the self-calibration bundle adjustment, three types of unknowns, namely, exterior orientation parameters, unknown space point coordinates, and model coefficients of the intrinsic parameters, are solved simultaneously. Experiments on three different digital cameras with zoom lenses support the feasibility of the proposed method, and their relative accuracies range from 1:4000 to 1:15,100. Furthermore, the nominal focal length written in the exchangeable image file header is found to lack reliability in experiments. Thereafter, the joint influence of zoom lens instability and zoom recording errors is further analyzed quantitatively. The analysis result is consistent with the experimental result and explains the reason why zoom lens calibration can never have the same accuracy as monofocal self-calibration.

Research on Light Pen Measuring System

Under the current situation of the rapid development of major equipment and technology, the research on measurement equipment, suitable for requirement of large-size application, is urgency and important. A light pen measuring system based on binocular stereo vision measurement principle is researched. The composition and working principle of the system are analyzed. Subpixel marginal fitting method is adopted to obtain the precise position of the center coordinates of the point of the coded marks. A mathematical model of the camera is Established, and the corresponding relations between the three-dimensional coordinates of the mark points in space and the two-dimensional coordinates of the same points in the image are deduced. In order to improve the speed and accuracy of image matching, the light reflection coded mark stickers are adopted as the marks of the light pen for imaging. The research on the key technologies of the light pen measuring system provides a theoretical basis for the further striking of three-dimensional coordinates of the space point, for the 3D reconstruction of the space model, and for the realization of software technology .

A 3D Reconstruction Method Based on Binocular View Geometry

A method was proposed to gain three-dimensional (3D) reconstruction based on binocular view geometry. Images used to calibrate cameras and reconstruct car’s rearview mirror by image acquisition system, by calibration image, a camera's intrinsic and extrinsic parameters, projective and fundamental matrixes were drawn by Matlab7.1;the collected rearview mirror images is pretreated to draw refined laser, extracted feature points, find the very appropriate match points by epipolar geometry principle; according to the camera imaging model to calculate the coordinates of space points, display point cloud, fitting space points to reconstruct car’s rearview mirror; experimental results show this method can better restore the car’s rearview mirror of 3D information.

Research on Accuracy Verification for Three-Dimensional Measurement Machine with Non-Contract and Surface Scanning

One kind of standard model equipment of three-dimensional coordinate measurement machine with non-contract curved surface used for verification solves accuracy standardization problems for the three-dimensional coordinate measurement machine with non-contract curved surface, then balls that are in different positions are used to replace collecting space point coordinates, next measurement errors of space line segment can be obtained through specific analysis and calculation. One new kind of accuracy verification method for the three-dimensional coordinate measurement machine is realized.

On relations for general two-dimensional ideal plasticity problems under the full plasticity condition

Relations for two-dimensional ideal plasticity problems under the full plasticity condition are determined with material anisotropy, inhomogeneity, and compressibility properties taken into account. These properties are determined by the direction cosines of the principal stress, the coordinates of points in space, and the mean stress.

Identification and geometrical modelling of complex shape surfaces using coordinate measuring machine and CAD/CAM systems

Two similar methods for the geometric identification of complex shape surfaces using the scanning measurement technique on a coordinate measuring machine (CMM) will be presented in this work. The first method employs the surfaces defined by the CAD system parametric technique based on the set of measurement points. The coordinates of points in space are determined by measurement in successive scanning planes with a given measuring step. The second method employs the surfaces defined by the analytically generated orthogonal curve meshes given by Newton's interpolation function. The interpolation points are the measurement points in the Cartesian space for a given measuring step. The generation technique of the interpolation function is then applied by using the interpolation method to define the arbitrary coordinate point set of the range of the measured net. Following this method of identification, some corrective procedure for measuring the results of surface coordinate points are proposed. These correction procedures result from use of the probe end in the coordinate technique. As a consequence of the presented corrective procedures, the authors propose useful software (numerical programmes) for the applied CMM during measuring of the complex shape surfaces. In the final part of the work, the sets of points obtained from these measurements are used to the develop 3D geometrical models of surfaces in the CAD system. The discussed techniques of identification and modelling are adopted in the design of a TV tube and the shape surface of the radial bone in bioengineering as practical examples.

Precision length measurement by computer-aided coordinate measurement

Gives a brief overview of computer-aided coordinate measurement as a method for testing the geometry of solid workpieces or components in mechanical engineering and similar fields. In contrast to conventional workpiece testing equipment, one can measure most kinds of workpiece with the coordinate measuring instrument as the only universal inspection centre. The principle is to measure a sample of surface points as space point coordinates, to evaluate them by means of mathematical models and computer software and to compute the desired sizes by using the computer's internal digital model of the workpiece. A brief description of the various measuring instruments, the best-fit evaluation algorithms according to Gauss and Tsebyshev, the uncertainty and the software for the new workpiece inspection method oriented on flexible manufacturing systems are given.

Experiments in Intensity Guided Range Sensing Recognition of Three-Dimensional Objects

With the advent of devices that can directly sense and determine the coordinates of points in space, the goal of constructing and recognizing descriptors of three-dimensional (3-D) objects is attracting the attention of many researchers in the image processing community. Unfortunately, the time required to fully sense a range image is large relative to the time required to sense an intensity image. Conversely, a single intensity image lacks the depth information required to construct 3-D object descriptors. This paper presents a method of combining the two sensory sources, intensity and range, such that the time required for range sensing is considerably reduced. The approach is to extract potential points of interest from the intensity image and then selectively sense range at these feature points. After the range information is known at these points, a graph structure representing the object in the scene is constructed. This structure is compared to the stored graph models using an algorithm for partial matching. The results of applying the method to both synthetic data and real intensity/range images are presented.

THE PROJECTIVE TRANSFORMATION IN AERIAL SURVEYING

The paper describes an algebraic method of forming linear equations, giving the coordinates of points in space in terms of the coordinates of their images on the photographic plates. The coefficients which enter into these linear equations form a matrix of the third order. When stereoscopic or similar methods are used for plotting detail, the elements of this matrix give in a convenient form and with the utmost obtainable accuracy the quantities required for setting the photographs in their correct relation to the map and to one another.An easy and rapid graphical method of obtaining good approximations to all the solutions of the problem of resection in space is described. A method of refining the solutions is given. When the coordinates of the air station are known with fair accuracy an alternative procedure is described. In the absence of ground control suitable for finding the air station by resection a method of eliminating most of the uncertain quantities is obtained. The indeterminate quantities relate to strip photographs as a whole and not to individual photographs. A method of dealing with the coefficients for the complete strip is described.In finding air stations by resection, point-coordinates in the photographs must be converted into directional coordinates. In other calculations this transformation is unnecessary.