3D S Parameters - Spatial Parameters
Std (Texture Direction)
Std, the texture direction,
is determined by the APSDF and is a measure of the angular direction of
the dominant lay comprising a surface. Std is defined
relative to the Y axis. Thus a surface with a lay along the Y axis will
return a Std of 0 deg.
(Note that Std is not strictly defined in the ISO 25178-2 but was established earlier in the research which contributed to ISO 25178-2. Future sections of ISO 25178-2 may address parameters such as Std)
Std= Major direction of lay derived from APSDF
Std is useful in determining the lay direction of a surface relative to a datum by positioning the part in the instrument in a known orientation. In some applications such as sealing, a subtle change in the surface texture direction may lead to adverse conditions. Std may also be used to detect the presence of a preliminary surface modification process (e.g. turning) which is to be removed by a subsequent operation (e.g. grinding followed by tumbling).