Feature parameters

The International Standards Organisation (ISO) will shortly be publishing the areal surface texture documents under the ISO number ISO/TS 25178. There are many innovative concepts introduced within this series of documents, amongst them is a distinction between two classes of surface texture parameters namely “Field” and “Feature” parameters.

Field parameters apply statistics to the continuous surface (cloud of points) from each portion of the scale-limited surface and include parameters such as: Sq, the root mean square of the surface height; Sz, the peak-to-valley of the surface height; Ssk, the skewness of the surface; Sdq, the root mean square of the surface gradient, etc.

Feature parameters apply statistics from a sub-set of pre-defined topographic features. Feature parameters are defined using a toolbox of pattern recognition techniques that can be used to characterise specified features on a scale-limited surface. The feature characterisation process is in five stages:

1.Selection of the type of texture feature
2.Segmentation
3.Determining significant features
4.Selection of feature attributes
5.Quantification of feature attribute statistics

The paper sets out to explain what feature parameters are, the rational behind them and the distinction between them and field parameters. A case study will be used to illustrate the ideas and usage of feature parameters.