Search

• Algorithms to calculate center of contrast targets are proprietary. • NIST's new algorithm enables transparency. • NIST's algorithm is robust and precise compared to OEM software. Terrestrial Laser Scanners (TLSs) are used in a variety of large scale scanning applications such as reverse engineering, assembly of aircraft or ships and surveying. Contrast targets are used with such instruments for enabling scene registration or to establish a scale when used on a scale bar. Currently, the algorithms to calculate the centers of contrast targets (CCT) are either proprietary to the original equipment manufacturers (OEMs) or not precise and accurate. Some of these algorithms may also operate only on OEM's proprietary data format. To overcome these limitations, a novel algorithm was developed at the National Institute of Standards and Technology (NIST) to calculate the center of contrast targets. Several targets in various orientations were scanned by one TLS and their centers were calculated by both the NIST algorithm and one OEM software. The results show that the NIST algorithm is robust, addresses many data quality issues and has better precision than the OEM software in most cases. [ABSTRACT FROM AUTHOR]

• A new Gaussian multivariate Laplace mixture (GMLM) distribution is presented to address the non-stationary heavy-tailed noises. • Resorting to a Bernoulli random variable, the distribution is expressed as hierarchically Gaussian presentation. • A novel robust nonlinear filter is proposed utilizing the GMLM distribution and variational Bayesian method. The estimation accuracy and estimation consistency of the proposed filter are illustrated by the simulation results. In this paper, the state estimation problems of nonlinear systems with outlier-corrupted measurements are investigated. First, to model the non-Gaussian noises caused by the randomly occurring measurement outliers, we propose a new Gaussian-multivariate Laplacian mixture (GMLM) distribution and analyze its distribution characteristics. Then, the measurement likelihood probability density function (PDF) is formulated as the GMLM distribution and further expressed as a hierarchical Gaussian expression. Furthermore, by variational Bayesian (VB) method, a robust cubature Kalman filter is derived (GMLMRCKF). Finally, simulation test and real date are utilized to evaluate the effectiveness of our GMLMRCKF, the results illustrate that the proposed filter has better estimation accuracy and consistence in the case of non-stationary heavy-tailed noises than the existing robust filters, i.e., it has almost the same performance as the standard CKF in the absence of outliers and better robust performance in the presence of unknown outliers. [ABSTRACT FROM AUTHOR]

Abstract: The Distributed Measurement Laboratory (DML) is an heterogeneous system and the workload evaluation is an important aspect to support the performance management strategies in case the specific requirements must to be respected. This paper describes the method to evaluate the workload of the co-operating hardware equipments of the DML, in particular: the connecting networks, and the PCs. In this manner useful indexes are achievable to monitor the functioning conditions of the whole DML. The proposed method is based on three different tools known and tested in the literature. The first one concerns with the synchronization among the clocks of the different co-operating PCs. The second one concerns the One-Way Delay parameter measurements of the path from the source to the destination. The third one concerns the workload measurement of the CPU of each PC. The results of several experimental tests showing the performance and the accuracy of the method are shown. Based on the analysis of these tests, some practical criteria can be inferred to point out performance management strategies. [Copyright &y& Elsevier]

• Method to evaluate performance of a laser tracker (LT) without need for scale bar. • Method utilizes stationary targets measured from multiple LT positions. • Length uncertainty between stationary targets is reduced by fitting LT error model. • These lengths are then used as reference for laser tracker performance evaluation. • Method validated using line-of-sight interferometry. Laser trackers (LTs) are widely used for large-scale dimensional metrology. Periodic LT performance evaluation is a key aspect in ensuring measurement reliability. The existing documentary standards for LT performance evaluation require scale bars and special artifacts that are often unavailable for many LT users. A network-based method is considered in this paper as a simple and effective approach to evaluate LT performance without the need for expensive artifacts or reference instruments. In this method, a set of fixed targets are measured from different locations of the LT. The reference values for the lengths between pairs of targets are determined by incorporating the geometrical error model of the LT (i.e., the LT data from each location are corrected for systematic geometric misalignments, quantities that are also obtained from the same data), thus the LT under test is itself used to calibrate the lengths in the network. Subsequently, these length values are used as references to evaluate the LT performance. We validate this method of establishing reference lengths by comparing the values for select lengths in the network against more traditional line-of-sight interferometry. We show that the uncertainties in the reference lengths obtained in this manner are sufficiently small in comparison to the maximum permissible error (MPE) specifications so that they can be used for performance evaluation. A case study using three LTs is presented in this paper. The results obtained from that case study is also verified by a simulation based on the ASME B89.4.19 standard, showing the feasibility of the proposed network-based LT performance evaluation method. [ABSTRACT FROM AUTHOR]

• 3-D printing used to manufacture primary standards for microwave measurements. • Printing using polymers; metal-plated to achieve required electrical performance. • Performance compares favourably with existing UK national standards. • New traceability approach proved: traceability originating at end-user locations. This paper describes the design, fabrication and testing of 3-D printed primary standards for use with the calibration of microwave vector network analysers. The standards are a short-circuit and a quarter wavelength section of line that are designed for use with the Thru-Reflect-Line calibration technique. The standards are realised in metal-pipe rectangular waveguide, covering the frequency range from 12 GHz to 18 GHz (i.e., Ku-band). The standards are polymer-based 3-D printed, which is subsequently metal plated to provide the required electrical conductivity. The performance of the standards is compared with conventionally machined standards that are used as part of the UK's primary national measurement system for microwave scattering parameters. The authors believe that this is the first time that 3-D printing techniques have been used to produce such calibration standards, and, that this could lead to a new approach to providing metrological traceability for these types of measurement. [ABSTRACT FROM AUTHOR]

• Report on first realization of test procedures per the ASTM E3125-17 standard. • Discuss test procedures, describe measurands and test methods. • Present the test values and their uncertainties. Spherical coordinate three-dimensional (3D) imaging systems, such as Terrestrial Laser Scanners (TLS), are already used widely in different fields. Their measurement performance evaluation is a topic of active research. In 2017, the first comprehensive documentary standard describing performance evaluation methods and procedures for TLS systems, the ASTM E3125-17, was released. In this paper, we report on the first realization of the test procedures per that standard. We briefly discuss the test procedures and then describe the materials and methods used to realize the tests. We then discuss the test measurands (the quantities of interest in the testing procedure), present the test values (the measured values of the test measurands), and the test value uncertainties (uncertainties in the testing process, which is typically the uncertainty in the reference length). The work described in this paper will serve as a useful reference for understanding and implementing the ASTM E3125-17 standard. [ABSTRACT FROM AUTHOR]

• Per ASTM E3125-17, TLS performance may be evaluated using long scale bars. • We report two methods to calibrate a scale bar with sphere targets mounted on it. • The four-orientation and two-face method is to calibrate horizontal bar length. • The comparison method is proposed for calibrating bar length in any orientation. • The validation experiments for the two methods are given and discussed. A scale bar with sphere targets is one way of realizing the symmetric and asymmetric length tests to evaluate Terrestrial Laser Scanner (TLS) performance per the ASTM E3125-17 standard. The length of the scale bar is required to be known with an expanded (k = 2) uncertainty that must be at least four times smaller than the manufacturer's maximum permissible error (MPE) specification of the instrument being tested. In this paper, we propose two methods to calibrate the scale bar length using a laser tracker. The first method, which we refer to as the four-orientation and two-face (FOTF) method, is proposed for calibrating the scale bar when it is in a horizontal orientation. The other method, which we refer to as the comparison method, is proposed for calibrating the length of the scale bar in any orientation. We describe the methods, present underlying theories, discuss validation experiments, and summarize results. The two calibration methods are beneficial for the realization of the ASTM E3125-17 standard for TLS performance evaluation. [ABSTRACT FROM AUTHOR]