Filters for contour measurement

Contour measurement requires the elimination of the radius of the tip. This process is sensitive to the noise in the measured data. Thus, the data of the trace of the centre of the tip has to be filtered. However, the Gaussian filtering is not the most appropriated for this purpose because it distorts the radius of small arcs in the profile and it is sensitive to spikes. The chosen morphological filter procedure is based on ISO/DTS/CD 16610-40 (ISO/TC213 WG 15). It is build as a set of several basic filter runs. The new morphological filter needs a minimum of settings, indeed, the only parameter to set-up is the nesting index, i.e. the radius of the filtering circular disk. This filter features a good suppression of spikes and gives the mean line between the upper and the lower envelope of a noisy trace. A comparison between Gaussian filtering and morphological filtering will be shown on an example of a recently developed contour standard. A standard filter radius of half the radius of the tip used for the measurements shows good results in most cases.