Overview of the softgauges package

Background

ISO 5436-2 (2001)[1] introduced into international standardization the concept of the software measurement standard or softgauge in the context of the measurement of surface texture. The standard defines Type F1 (reference data) and Type F2 (reference software) measurement standards for testing the software aspects of instruments for the measurement of surface texture. The standard also defines the file format SMD for Type F1 measurement standards.

ISO 4287 (2000)[4] defines a number of surface texture parameters that are used to associate numerical values with the topography of a surface. In practice, the parameters are evaluated in terms of digital data representing a two-dimensional profile, which may be a primary (P) profile or, following the application of a filter to the primary profile, a roughness (R) or waviness (W) profile for the surface.

This software package constitutes reference software for the calculation of surface texture parameters defined in ISO 4287 (2000)[4].

Functionality

The input to the software is an SMD file consistent with the requirements of ISO 5436-2 (2001)[1].

The software implements calculations of the surface texture parameters

• Pa, Ra, Wa
• Pq, Rq, Wq
• Psk, Rsk, Wsk
• Pku, Rku, Wku
• Pp, Rp, Wp
• Pv, Rv, Wv
• Pz, Rz, Wz
• PSm, RSm, WSm
• Pc, Rc, Wc
• Pt, Rt, Wt

consistent with ISO 4287 (2000)[4].

For the calculation of roughness and waviness parameters, the software implements a Gaussian filter with cut-off lambdaC consistent with ISO 11562 (1996)[6].

Two main assumptions are made about the profile for which the above parameters are to be calculated. Firstly, that the profile has been filtered to remove form and components shorter than those associated with roughness (lambdaS-filtered). Secondly, the profile is digitised in such a way that positions of the points are uniformly spaced, and strictly increasing, along the X-axis. (In fact, the software will use information provided in the input SMD file to construct X-values to satisfy the second of these assumptions.)

In addition, for the implementation of the Gaussian filter the following recommendations are applied. Firstly, in order minimise distortion at the ends of the profile one cut-off length at each end of the profile is removed following application of the filter. Secondly, in order to minimise the distortion of the profile due to its finite length the minimum number of cut-off lengths in the profile is required to be three. Lastly, in order to minimise the distortion of the profile due to its digitisation the minimum number of points per cut-off length is required to be fifty.

A reference value is provided for each surface texture parameter listed in the input SMD file. The reference value is provided in output files, of types SMD and HTML, generated by the software. The (measurement) uncertainty associated with the reference value is not provided (and a value of zero is written to the output file of type SMD): the evaluation of the uncertainty would require knowledge of the (measurement) uncertainties associated with the Z-values defining the measured profile (and these are not part of the SMD file format). The reference values are provided to assess the numerical correctness of the values provided by test software for the calculation of the above surface texture parameters.