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razorback
05-13-2009, 08:59 PM
Its common knowledge that light falls off over and inverse square of distance, so I am wondering if the scale of the models that we build in maya need to be adjusted to the correct scale in world space for it to deliver the most realistic results. If so, does sun and sky take into account the working units and changing the default from say, cm to meters ?

spiralof5
05-13-2009, 11:09 PM
Hey razorback,

I am not sure if it matters your scene size. My first inkling is to say that since it is a physically accurate model then, yes, you should build to scale of unit size.

Having said that, since Maya is notorious for having multiple problems when changing unit size from 1 cm = 1 unit to anything, period, you should always build in cm. A quick type of google and you will get results for cm to inches/feet converters. Also, in the realm of realistic skin, if you ever get into that, you need to build to correct size anyway because the Mental Ray fast skin shader deals with realistic proportions.

Also, if you work with Final Gather, and you use the radius min and max attributes, they are either dependent on your resolution (if you are working with pixel to pixel radius) or scene size. I don't know how that would affect anything but it's something to think about.

Having said that, you can use the min and max boundary box in the Physical Sun portion of the sun sky solution so that you limit the rays to only that box. I think if you are dealing with issues of scene size and render times, using this can help.

Most generally, as a rule of thumb when working with realistic scenes, you should always build to scale. I'm not 100% on this so take my advice with a grain of salt, maybe.

Scott

royterr
05-14-2009, 05:38 PM
After a long research, it turns out that sticking with cm is the best choice for all modules.
But the real question in this case, is whether you model a 10 meters length room (in the real world) by giving it 10 units (so 10cm) or 1000 units (so 1000 cm).

InfernalDarkness
05-14-2009, 09:13 PM
...I'm going from Rhino (inches) to Maya (centimeters), but the .obj file format appears to not really care what units I'm using. So my typical workflow is to export from Rhino to .obj (leaving my Rhino geometry alone, as inches/feet) to Maya, where I typically group everything imported and scale down by ten (.1, .1, .1). If I leave my geometry at Rhino's scale, all kinds of FG and GI issues arise, and I typically have to increase the scale of my GI and FG from 1 to 10 to get anywhere near realistic lighting. This is regarding both the Sun/Sky as well as regular MR lights. As it stands, I still generally increase my FG scale to 2 or 4, or else I won't get much of any indirect lighting. At 1 (default), FG is useless in my scenes.

I have not experienced "photometric accuracy" yet, nor do I know how to go about making that happen. Maya simply prefers centimeters; I could scale down/up by the .254 factor, but when scaling down this way my lights need to be cranked way up.

So, typically I just reduce everything by 10 and ignore any kind of physical accuracy. This works fine for me, since I don't model my interiors/exteriors in Maya much, and also since Maya has no tools for CAD to speak of. I basically just use Maya professionally for rendering my Rhino scenes.

Other people will assuredly have other workflows or demand more accuracy in Maya.

spiralof5
05-15-2009, 09:18 PM
After a long research, it turns out that sticking with cm is the best choice for all modules.
But the real question in this case, is whether you model a 10 meters length room (in the real world) by giving it 10 units (so 10cm) or 1000 units (so 1000 cm).

Well, I know what you are saying. I've read that people do this type of thing often saying that a unit is a unit, a unit can be 1 cm, 1 m, 1 km but here's the kicker; when working with the fast skin, again, the shader reads as 1 cm = 1 unit.

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