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.

Sdr of a completely level surface is 0.
Sdr (Developed interfacial area ratio)

When a surface has any slope, Sdr becomes larger. The following surface is a plane with gradient components of 45 degrees and its Sdr is 0.414. (This means that the surface area has increased by slightly more than 40%.)
Sdr (Developed interfacial area ratio)

Sdr (Developed interfacial area ratio)

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Height	Sa (arithmetical mean height)
Sz (Maximum height)
Sq (Root mean square height)
Ssk (Skewness)
Sku (Kurtosis)
Sp (Maximum peak height)
Sv (Maximum pit height)
Spatial	Sal (Auto-correlation length) / Str (Texture aspect ratio)
Std* (Texture direction)
Hybrid	Sdq (Root mean square gradient)
Sdr (Developed interfacial area ratio)
Functional	Smr(c) (Areal material ratio)
Smc(mr) (Inverse areal material ratio)
Sk (Core roughness depth)
Spk (Reduced peak height)
Svk (reduced dale height)
Smr (Peak material portion)
Smr2 (Valley material portion (percentage of the measurement area that comprises the deeper valley structures associated with Svk))
Sxp (Peak extreme height)
Functional volume	Vvv (Dale void volume)
Vvc (Core void volume)
Vmp (Peak material volume)
Vmc (Core material volume)
Feature	Spd (Density of peaks)
Spc (Arithmetic mean peak curvature)
S10z / S5p / S5v / Sda(c) / Sha(c) / Sdv(c) / Shv(c)

Height

Sa (arithmetical mean height)

Sz (Maximum height)

Sq (Root mean square height)

Ssk (Skewness)

Sku (Kurtosis)

Sp (Maximum peak height)

Sv (Maximum pit height)

Spatial

Sal (Auto-correlation length) / Str (Texture aspect ratio)

Std* (Texture direction)

Hybrid