> Chris Cason <del### [at] deletethistoopovrayorg> wrote:
>> The algorithm is designed to give realistic results at a scale of 10 mm per
>> POV-Ray unit by default; for other scales, place the following statement in
>> the global_settings section:
>>
>>   mm_per_unit NUMBER
> 
> Hi I'm new here, I'm a blenderhead. this SSTL feature attracted me to Povray.
> What a beautiful piece of software!
> My question is whether this mm_per_unit option was added just for SSTL and
> applies only to it (which is not clued by the currently chosen keyword) or if
> it will also have an incidence over the whole scene's scale and stuff like
> photons, radiosity scale etc...?
> Using Blend2pov and trying to make a skin shader, my current scale is 1 meter
> per Blender Units, and I guess keeping the same in Pov units would make it
> easier for me to get more intuitive and predictable results with other Pov
> features later. So I tried mm_per_unit 1000 but I could not get the same
> translucency with SSTL as I could achieve with mm_per_unit 100, which is indeed
> closer to what the algorithm is optimized for.
> 
> 
> 

The mm_per_unit is ONLY used for the new SSLT feature. Before it's 
introduction, that keyword did not exist. If you try to use it with any 
version older than 3.7 beta 31, the parsing will give you an error about 
an undefined user variable and stop.

This is because, SSLT is dependent on the actual "real" distences 
traveled into the substence.
If you set it to 1000, it's normal that the effect is smaller and less 
pronounced than if it's set to 100. In fact, it will be 10 about times 
less visible.

I don't think that the algorythm is optimised for a value of 100, it's 
just the default value.

Anywhere else, a POV-unit is just an arbitrary unit that can represent 
whatever real world unit you like. Be it a nanometer or a kilo parsec, 
or anything in between.




Alain

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