National Physical Laboratory

Software for the Evaluation of Areal Surface Texture Function and Feature Parameters

The Project

The project 'Measurement and characterisation of areal surfaces' carried out the following activities:

  • Development of unambiguous definitions and specifications of algorithms for areal filtering and evaluating areal surface texture parameters;
  • Implementation of reference software consistent with those definitions and specifications.

The project, supported by the National Measurement Office of the UK Department for Business, Innovation and Skills as part of its Engineering and Flow Programme, October 2011 – September 2014, was carried out by NPL, in partnership with the Centre for Precision Technologies at the University of Huddersfield.


The main functions of the software are as follows:

  • Read data defining an S-F surface, i.e. a surface that has been S-filtered (to remove small scale components) and from which form has been removed (using an F-operator)
  • Apply a Gaussian areal filter to the data defining an S-F surface to obtain data defining the corresponding S-L surface
  • Remove points from the data defining an S-L surface, i.e. 'trim' the data, to produce a surface defined on an area that has sides with lengths that are integer multiples of the cut-off wavelength for the Gaussian areal filter used to obtain the surface
  • For function parameters
    • Evaluate approximations to the inverse areal material ratio functions for the S–F and S–L surfaces in the form of (shape-preserving) cubic spline interpolants to data defining those functions
    • Evaluate function parameters in terms of those representations of the inverse areal material ratio functions
  • For feature parameters:
    • Apply segmentation to data defining the S–F and S–L surfaces to identify significant features of those surfaces
    • Evaluate feature parameters in terms of those significant features of the S–F and S–L surfaces
  • Write the values of the areal surface texture parameters to a simple text output file


The areal surface texture parameters to be evaluated include function parameters Sk (core height), Smr1 (peaks material ratio), Smr2 (dales material ratio), Spk (reduced peak height), Svk (reduced dale height), Sxp (peak extreme height), Vmp (peak material volume), Vmc (core material volume), Vvv (dale void volume), and Vvc (core void volume), and feature parameters Spd (density of peaks), Spc (arithmetic mean peak curvature), S5p (five-point peak height), S5v (five-point pit height), S10z (ten-point height of surface), Sda(c) (mean dale area), Sha(c) (mean hill area), Sdv(c) (mean dale volume), and Shv(c) (mean hill volume).


To download the software it is necessary to complete a simple registration form

The software is provided as a compressed .ZIP folder containing:

  • A user manual describing how to install and use the software
  • A software user license agreement (REF: MSC/L/15/001)
  • A 'readme' file
  • The executable FunctionFeatureCharacterisationSoftware.exe
  • The auxiliary files:
    • ISO5436_2_XML.dll
    • xerces-c_2_7_vc80.dll
    • tbb.dll
    • openX3P.mexw32
    • writeX3P.mexw32
    • iso5436_2.xsd
    • npl_logo_black_large.jpg
  • An example data file with corresponding output file

Users are encouraged to read the user manual and 'readme' file before using the software.

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Last Updated: 5 Jul 2017
Created: 5 Jul 2017


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