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What units are used for "real world" material values?

Message 1 of 2
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What units are used for "real world" material values?

There are a number of material parameters that relate to real-world values (for example, subsurface radius). What units does Arnold use under the hood for these values?


When rendering with the API, materials with subsurface scattering don't look right. I can get them to match Maya/MtoA if I change my SSS scale to 0.01, though, which leads me to believe that I should be doing some kind of conversion from meters to cm in order for this to render properly (ie, rendering with a scale of 0.01 in the API matches Maya/MtoA with a scale of 1). But, I don't know if this conversion is limited to JUST subsurface settings or if I need to do something globally to make sure my materials look physically accurate. Any help is appreciated!

Message 2 of 2
in reply to: AaronWPowell

What units does Arnold use under the hood for these values?

A renderer is not a dimensional system, internally, - everything is unitless.

Think for example about radians vs degrees and why radians are native in a renderer. Radians are based on the ratio of the length of an arc to the radius of a circle. This means that when you measure an angle in radians, you're essentially comparing two lengths so the unit "radian" is actually dimensionless because it represents the ratio of two lengths, which cancel each other out.

Even if SSS radius is divided by 100 internally it is only for practical use and so they are not necessarly centimeters.

Eventually a plugin may enforce dimensionality by cooking values before passing them to the renderer.



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