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Publication Citation: Fitting Weighted Total Least-Squares Planes and Parallel Planes to Support Tolerancing Standards

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Author(s): Craig M. Shakarji; Vijay Srinivasan;
Title: Fitting Weighted Total Least-Squares Planes and Parallel Planes to Support Tolerancing Standards
Published: October 19, 2012
Abstract: We present elegant algorithms for fitting a plane, two parallel planes (corresponding to a slot or a slab) or many parallel planes in a total (orthogonal) least-squares sense to coordinate data that is weighted. Each of these problems is reduced to a simple 3×3 matrix eigenvalue/eigenvector problem or an equivalent singular value decomposition problem, which can be solved using reliable and readily available commercial software. These methods were numerically verified by comparing them with brute-force minimization searches. We demonstrate the need for such weighted total least-squares fitting in coordinate metrology to support new and emerging tolerancing standards, for instance, ISO 14405-1:2010. The widespread practice of unweighted fitting works well enough when point sampling is controlled and can be made uniform (e.g., using a discrete point contact Coordinate Measuring Machine). However, we demonstrate that nonuniformly sampled points (arising from many new measurement technologies) coupled with unweighted least-squares fitting can lead to erroneous results. When needed, the algorithms presented also solve the unweighted cases simply by assigning the value one to each weight. We additionally prove convergence from the discrete to continuous cases of least-squares fitting as the point sampling becomes dense.
Conference: The ASME 2012 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference
Proceedings: Proceedings of the ASME 2012 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference
Volume: 2
Pages: pp. 449 - 459
Location: Chicago, IL
Dates: August 12-15, 2012
Keywords: coordinate metrology; computational metrology; least-squares; plane; plane fitting; point sampling; sampling; surface fitting; total least-squares; weighted least-squares fitting; weighted fitting; parallel plane fitting; tolerance
Research Areas: Software, Length, Manufacturing
DOI: http://dx.doi.org/10.1115/DETC2012-70398  (Note: May link to a non-U.S. Government webpage)
PDF version: PDF Document Click here to retrieve PDF version of paper (186KB)