Calibration

Abstract: A new technique for three-dimensional (3D) camera calibration for machine vision metrology using off-the-shelf TV cameras and lenses is described. The two-stage technique is aimed at efficient computation of camera external position and orientation relative to object reference coordinate system as well as the effective focal length, radial lens distortion, and image scanning parameters. The two-stage technique has advantage in terms of accuracy, speed, and versatility over existing state of the art. A critical review of the state of the art is given in the beginning. A theoretical framework is established, supported by comprehensive proof in five appendixes, and may pave the way for future research on 3D robotics vision. Test results using real data are described. Both accuracy and speed are reported. The experimental results are analyzed and compared with theoretical prediction. Recent effort indicates that with slight modification, the two-stage calibration can be done in real time.

Abstract: A camera model that accounts for major sources of camera distortion, namely, radial, decentering, and thin prism distortions is presented. The proposed calibration procedure consists of two steps: (1) the calibration parameters are estimated using a closed-form solution based on a distribution-free camera model; and (2) the parameters estimated in the first step are improved iteratively through a nonlinear optimization, taking into account camera distortions. According to minimum variance estimation, the objective function to be minimized is the mean-square discrepancy between the observed image points and their inferred image projections computed with the estimated calibration parameters. The authors introduce a type of measure that can be used to directly evaluate the performance of calibration and compare calibrations among different systems. The validity and performance of the calibration procedure are tested with both synthetic data and real images taken by tele- and wide-angle lenses. >

Abstract: The author presents a method for the calibration of network analyzers. The essential feature is the use of multiple, redundant transmission line standards. The additional information provided by the redundant standards is used to minimize the effects of random errors, such as those caused by imperfect connector repeatability. The resulting method exhibits improvements in both accuracy and bandwidth over conventional methods. The basis of the statistical treatment is a linearized error analysis of the TRL (thru-reflect-line) calibration method. The analysis presented is useful in the assessment of calibration accuracy. It also yields results relevant to the choice of standards. >

Abstract: Time domain reflectometry (TDR) has been developed to an operational level for the measurement of soil water content during the past decade. Because it is able to provide fast, precise and nondestructive in situ measurements, it has become an alternative to the neutron scattering method, in particular for monitoring water content under field conditions. One of the major disadvantages of the neutron scattering technique is that, due to the relatively high sensitivity of the signal to factors other than water content, site-specific calibration is usually required. In this paper a calibration curve for the TDR method is presented which is not restricted to specific soil conditions. The calibration is based on the dielectric mixing model of Dobson et al. (1985). Measurements of volumetric water content and dielectric number at eleven different field sites representing a wide range of soil types were used to determine the parameter of the model by weighted nonlinear regression. The uncertainty (root mean square error) of water content values calculated with the optimized calibration curve was estimated not to exceed 0.013 cm3/cm3. This value is comparable to the precision of the thermogravimetric method. From a sensitivity analysis it was determined that the temperature dependence of the TDR signal may have to be corrected to obtain optimum accuracy.

Abstract: Foreword by Professor D. Dowson GENERAL PHILOSOPHY OF MEASUREMENT Where does surface metrology fit in engineering metrology? Importance of surface metrology SURFACE CHARACTERIZATION-THE NATURE OF SURFACES AND THE SIGNALS OBTAINED FROM THEM Surface roughness characterization Waviness Errors of form Comparisons of definitions for surface metrology and coordinate measuring Characterization of defect shapes on the surface PROCESSING Digital methods Digital properties of random surfaces Fourier transform and the FFT Statistical parameters in digital form Properties and implementation of ambiguity function and Wigner distribution function Digital estimation of reference lines for surface metrology Algorithms Transformation in surface metrology Graphical methods Other methods of processing Surface generation INSTRUMENTATION Introduction and historical Measurement systems Optical techniques for measurement of surfaces Capacitance techniques for measurement of surfaces of slopes Inductance techniques Impedance technique-skin effect Other non-standard techniques Electron microscopy Merit of transducers ERRORS, CALIBRATION, TRACEABILITY AND STANDARDIZATION Nature of errors Deterministic or systematic error model Basic components of accuracy evaluation Basic error theory for a system Propagation of errors Some useful statistical tests for surfaces Uncertainty in instruments-calibration in general Calibration of stylus instruments Calibration of form instruments Parameter variation National and international standards Drawing symbols SURFACE METROLOGY IN MANUFACTURE Manufacturing processes Cutting Abrasive processes Unconventional machining Surface roughness produced by machining difficult materials Surface effects other than geometry Surface geometry-a fingerprint of manufacture SURFACE GEOMETRY-ITS IMPORTANCE IN FUNCTION Two body interaction - static effects Functional properties of contact Two body interactions - dynamic effects General roughness and system life One body interactions One body with radiation (optical) Scattering by other waves Systems function SUMMARY AND CONCLUSIONS Characterization and nature of signal Data processing Measurement of trends Calibration Manufacture Function Overview