Meaning
Spatial filtering specifications govern the operator guidelines for separating micro-roughness from macro-form in surface texture analysis. In optical metrology of polymer parts, ISO 25178-3 defines default nesting indices and filter transmission characteristics. The standard stops applying once surface data has been filtered and parameter calculation begins.
Filter Selection
Roughness measurement requires removing low-frequency waviness and high-frequency noise from raw topography datasets. Under the specifications of ISO 25178-3, optical instruments apply S-filters and L-filters using Gaussian or spline algorithms to establish the scale of interest. Choosing an incorrect nesting index distorts reported roughness parameters, causing false passes or rejections during quality inspection of injection mold cavities.
Standardized bandwidths ensure reproducible surface evaluations across different measurement devices. Proper filter selection prevents form errors from skewing micro-texture values.
Transmission Bandpass
Scale-limited surfaces result from passing raw height maps through defined spatial cutoffs. Principles in ISO 25178-3 specify how instrument transfer functions modify transmission amplitude across intermediate spatial frequencies.
Specification Boundary
Metrology protocols must document the exact filter types and nesting indices applied during measurement. Operating under ISO 25178-3 guarantees that independent laboratories produce identical surface roughness numbers from the same physical sample. Component drawings for plastic optics specify nesting limits to standardize vendor verification procedures.
Failure to record filtering settings renders areal surface measurements uninterpretable.
