The coarse-to-fine method is the prime technology for point cloud registration in 3D reconstruction. Aimed at the problem of low accuracy of coarse registration for the partially overlapping point clouds, a novel, to the best of our knowledge, 3D local feature descriptor named grid normals deviation angles statistics (GNDAS) for aligning roughly pairwise point clouds is proposed in this paper. The descriptor is designed by first dividing evenly the local surface into some grids along the x axis and y axis of the local reference frame, then making the statistics of the deviation angles of normals at grid points. Based on the correspondences generated by matching descriptors and a transformation estimation method, the initial registration result is obtained. The coarse registration result is used as the initial value of the iterative closest point algorithm to achieve the refinement of the registration result. Experimental comparisons on two public datasets demonstrate that our GNDAS descriptor has high descriptiveness and strong robustness to noise at low level and varying mesh resolution. The registration results also confirm the superiority of our registration approach over previous versions in accuracy and efficiency.

Vision measurement has encountered the bottlenecks in capturing and processing the images of laser spots under harsh working environment of strong sunshine and complex background. Breaking through the camera calibration, we propose that the corresponding relationship between pixel coordinates of laser spots, but not the camera, and measurement distances generated from laser rangefinder is directly calibrated under good working environment. The pixel coordinates of laser spots can be obtained from the calibration model and measurement distances during practical measurement. The imaging of laser spots by camera is no longer needed. Experimental results demonstrate that the measurement errors are in the millimeter level within 20 m distance outdoors.

An articulated laser sensor, which is a new kind of trans-scale, non-contact metrological instrument, is principally made up of two articulated laser sensing modules. Each module is composed of two rotary tables and one collimated laser. Calibrating the spatial pose of a laser beam is a key aspect of the measurement system. In this paper we propose a one-dimensional linear displacement optical calibration device for high stability and easily performed calibration. Through analysis of space vectors and image processing, a calibration method for spatial pose of the laser beam is introduced in detail. The calibration method is divided into two parts: calibration of the direction vector of the laser beam and a fixed point on the laser beam. Firstly, the direction vector of the laser beam is calibrated using the proposed calibration device. Then a set of points on the laser beam is obtained and the linear fitting is performed. By comparing the direction vector of the fitted line and the direction vector of the above laser beam, the optimal fixed point on the fitted line is obtained. The simulation and experimental results show that the proposed calibration method is accurate and effective.

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Breaking through the orthogonal shafting architecture of traditional measurement instruments, a novel articulated laser sensor for three-dimensional (3D) precision measurement is proposed. The novel sensor consists of two articulated laser sensing modules, and each module is mainly made up of two one-dimensional rotary tables and one collimated laser to achieve a flexible angle intersection. Moreover, a high-resolution digital camera is mounted on the right sensing module to achieve vision guidance. The three axes of each sensing module represent a non-orthogonal shafting architecture. The requirements of structural design, material selection, processing technology, assembling, calibration and maintain are greatly lowered. The costs are greatly reduced, including time and money. The system architecture, parameter calibration and measurement principle are elaborated. An accurate intersection model of two laser beams is proposed to calculate the accurate rotation angles of rotary tables by discrete point interpolation method. The experimental results showed that a maximum error less than 0.05 mm was detected from 100 mm to 500 mm. It is proved that 3D precision measurement is feasible with this proposed articulated laser sensor.INDEX TERMS Articulated laser sensor, non-orthogonal shafting architecture, 3D precision measurement, accurate intersection model.