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Unformatted text preview: ion. In addition, many CMM manufacturers implement their own proprietary programs without explicitly stating the underlying assumptions and limitations of their algorithms. The discrepancies between the evaluation results from different evaluation software programs, for the same set of data points, can be as large as 50% [Yau, 1999]. Appropriate consideration of measurement planning, estimation of the best substitute geometry and uncertainty analysis as inter-related issues is essential. The work presented by Nassef and ElMaraghy shows that the performance of the error function for the best fitting, depends on the number of measured points relative to the number of points that would ideally represent the whole surface, the type of the geometric deviation and the inherent errors in the measuring system [Nassef & ElMaraghy, 1999]. 2.1. Fitting of Substitute Geometry Fitting substitute geometry to the data points by minimizing an error objective function is defined by the Lp-norm equation [Hopp, 1993]: 1 n p L p = ∑ ri n i 1/ p...
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