Sdr (Developed Interfacial Area Ratio)
This parameter is expressed as the percentage of the definition area's additional surface area contributed by the texture as compared to the planar definition area.
The Sdr of a completely level surface is 0.
When a surface has any slope, its Sdr value becomes larger. The surface below is a plane with gradient components of 45 degrees and has an Sdr value of 0.414.