3D Measurement Model Research Articles

A Non-Contact Measurement of Animal Body Size Based on Structured Light

To improve the accuracy of non-contact measurements of animal body size and reduce costs, a new monocular camera scanning equipment based on structured light was built with a matched point cloud generation algorithm. Firstly, using the structured light 3D measurement model, the camera intrinsic matrix and extrinsic matrix could be calculated. Secondly, the least square method and the improved segment–facet intersection method were used to implement and optimize the calibration of the light plane. Then, a new algorithm was proposed to extract gray- centers as well as a denoising and matching algorithm, both of which alleviate the astigmatism of light on animal fur and the distortion or fracture of light stripes caused by the irregular shape of an animal’s body. Thirdly, the point cloud was generated via the line–plane intersection method from which animal body sizes could be measured. Finally, an experiment on live animals such as rabbits and animal specimens such as fox and the goat was conducted in order to compare our equipment with a depth camera and a 3D scanner. The result shows that the error of our equipment is approximately 5%, which is much smaller than the error of the other two pieces of equipment. This equipment provides a practicable option for measuring animal body size.

Coding line structured light based on a line-scan camera and its calibration.

In a conventional three-dimensional (3D) measurement technique of a line-scan camera, the projection system based on surface structured light is a compromise of traditional projection technology, which suffers from complex calibration, complex structure and low accuracy. To this end, the coding line structured light based on the coded line laser projection system is proposed to address the 3D measurement of a line-scan camera. The single-line projection and codeable characteristics of coded line laser projection system (constructed by a point laser and a micro-electro-mechanical system (MEMS) scanning galvanometer and modeled as the line projection model) are fully matched with the imaging mode of the line-scan camera. The 3D measurement model based on the height information, lateral information and absolute phase of the coding line structured light is derived. The multi-position flat display calibration method is proposed to calibrate the system parameters. In addition, in order to obtain the accurate absolute phase from the phase shift combined binary code, the periodic error correction method based on expansion-corrosion is proposed to correct the phase error. Contrary to conventional structured light methods based on a line-scan camera, the proposed method has the advantages of high measurement accuracy, high efficiency, more compactness and low cost. The experiments affirm that the coding line structured light is valid and the proposed calibration method is feasible. Experimental results also indicate that the proposed method performs well for both diffuse reflective surfaces and reflective surfaces that are difficult to measure with conventional structured light methods based on a line-scan camera.

Monitoring and Assessing the Dynamics of Building Deformation Changes in Landslide Areas

The paper presents the procedure and results of monitoring conducted by using a 3D measurement model, taking advantage of integrated surveying technologies developed for a building located within an activated landslide area. Geodynamic interactions within the building have resulted in a spatial deformation condition, leading to significant cracks of structure components and local basement floor upheavals. Conducted site research shows a reactivation of an old landslide form. To provide safe use conditions for the building, it was decided to monitor the structure and the area in its vicinity. Meeting this demand required developing an in-house monitoring system for the landslide form and the very structure. Measurements provided detailed information on the sizes and directions for the displacements of ground surface points and building structure points, as well as the dynamic properties of this phenomenon. Obtained results show the opportunity to use monitoring systems to acquire credible measurements data reflecting the real impact of ground landslide deformations on structures.

Research on 3D measurement model by line structure light vision

For serious radial distortion and high precision measurement, 3D measurement model is studied in the paper. Based on the two-step calibration algorithm, a round initialization window is proposed to calculate the initial value of the camera parameters for nonlinear optimization. In order to solve the problem that the Supersonic Transport Evaluation Group algorithm of light stripe center extraction has a large amount of computation, a method is presented by normalized correlation coefficient (NCC) method and principal component analysis (PCA). Finally, the coordinates of the central stripe could be obtained based on the bilinear interpolation and parabolic fitting. With the parameters of the structured light plane that could be obtained by the coordinates of the central stripe, the height of block gauge is measured by the 3D measurement model. The experiment results showed that the average measurement error is 0.0191 mm, and the strip extraction speed is improved.

一字线结构光三维测量模型的新型标定方法

A machine vision measurement model of line structured-light was established.Based on the improved camera calibration method,an accurate calibration method of structured-light plane was proposed.According to the distribution of the structured-light′s energy along the normal direction of the light′s plane,Gauss fitting method was used to extract the sub-pixel coordinates of the light stripe′s center point on the image.In the calibration,the local world coordinate system was established on the surface of the free-moving planar target.Then,the local world coordinates of the stripe′s center point,which were obtained by the parameters of the camera calibration,were translated into the camera coordinate system.Using the obtained calibration points on the light plane,the plane of the structured-light was estimated in the camera coordinate system.The factors that would affect the precision of the measurement model were fully considered in this method,which could achieve a large number of calibration points.From the measurement of standard gauge block and shaft diameter,this method has high precision in practice.

Monocular SLAM with undelayed initialization for an indoor robot

This paper presents a new feature initialization method for monocular EKF SLAM (Extended Kalman Filter Simultaneous Localization and Mapping) which utilizes a 3D measurement model in the camera frame rather than 2D pixel coordinates in the image plane. The key idea is to regard a camera as a range and bearing sensor, of which the range information contains numerous uncertainties. 2D pixel coordinates of measurement are converted to 3D points in the camera frame with an assumed depth. The element of the measurement noise covariance corresponding to the depth of the feature is set to a very high value. And it is shown that the proposed measurement model has very little linearization error, which can be critical for the EKF performance. Furthermore, this paper proposes an EKF SLAM system that combines odometry, a low-cost gyro, and low frame rate (1–2 Hz) monocular vision. Low frame rate is crucial for reducing the price of the processor. This system combination is cost-effective enough to be commercialized for a real vacuum cleaning application. Simulations and experimental results show the efficacy of the proposed method with computational efficiency in indoor environments.

A Novel Approach to Calibrating Multifunctional Binocular Stereovision Sensor

We present a novel multifunctional binocular stereovision sensor for various threedimensional (3D) inspection tasks. It not only avoids the so-called correspondence problem of passive stereo vision, but also possesses the uniform mathematical model. We also propose a novel approach to estimating all the sensor parameters with free-position planar reference object. In this technique, the planar pattern can be moved freely by hand. All the camera intrinsic and extrinsic parameters with coefficient of lens radial and tangential distortion are estimated, and sensor parameters are calibrated based on the 3D measurement model and optimized with the feature point constraint algorithm using the same views in the camera calibration stage. The proposed approach greatly reduces the cost of the calibration equipment, and it is flexible and practical for the vision measurement. It shows that this method has high precision by experiment, and the sensor measured relative error of space length excels 0.3%.

Complete calibration of a structure-uniform stereovision sensor with free-position planar pattern

We present a novel structure-uniform stereovision sensor for variable 3D inspection tasks. In this paper, the mathematical model of the stereovision sensor is established. A flexible approach to estimate all the primitive parameters of the stereovision sensor with free-position planar pattern is proposed. In this technique, without restriction to the moving of the planar reference object, all the camera parameters with coefficient of lens radial and tangential distortion can be readily calibrated, and based on the 3D measurement model of stereovision sensor, the sensor parameters can be optimized with the feature points constraint algorithm simultaneously. The proposed approach greatly reduces the cost of the calibration equipment, and it is flexible and practical for the vision measurement. It shows that this method has high precision by experiment, and the measured relative error of space length excels 0.3%.

Color 3D reverse engineering

This paper presents a principle and a method of color 3D laser scanning measurement, based on the fundamental of monochrome 3D measurement study. A new color 3D measurement model was derived, and a rapid calibrating method to measure the system parameters was proposed—the optical plane equation calibrating method. A calibrating drone was made. This paper also advances an auto-merging method for multi-frame, i.e. several frames of measured color 3D digital images are merged quickly according to their curvature characteristics and RGB information, in order to accomplish the complete color 3D digital model of the object. The system can be broadly used in the fields of product design, mold manufacture, multi-media, game development, animation, medical engineering, antique digitization, etc.