Unit scale

[tmcthree]

Hey,
How does Vray handle units in Maya? With my pipeline it would be very helpful if I could use metres, but I seem to remember reading somewhere that vray needs to work in centimetres? Is this correct?

I'm trying to set up a physical camera in a scene using metres but I'm having to use some ridiculous values just to make the object visible f1, iso >40000. So I'm guessing this is a scale issue.

Is there any place in vray where I have to set the scale units to match mayas scale units?

Thanks in advance

[joconnell]

How bright are your light sources? Are you trying to use light multipliers around 1 but with lights that are using decay? There's something very wrong sounding about the camera values you're using - what type of shutter speeds?

[tmcthree]

How bright are your light sources? Are you trying to use light multipliers around 1 but with lights that are using decay? There's something very wrong sounding about the camera values you're using - what type of shutter speeds?

The lights are at Intensity 30 and decay is on. Without using a physical camera it looks fine.
If I turn physical camera on, then in order for the image to be about the same brightness as the image with no camera I have to set the values f-5, shutter speed 3 and iso 40,000. So, stupid values!

If I set maya scale units to centimetres rather than meters then the image gets very bright with those values as you'd expect.
Is there a separate scale unit for Vray I have to set somewhere? A multiplier or something?

[vlado]

V-Ray will read whatever units you have set in the Maya preferences. If you want those units to be different from your render units, then this can be done with a Python post-translate callback, like this:

from vray.utils import *
p=findByType("SettingsUnitsInfo")
p[0].set("meters_scale", 1.0) # Here 1.0 is conversion factor from scene units to meters, you can change it accordingly

Best regards,
Vlado

[tmcthree]

Hmmm, if Vray does take account of the scale, why do I need such crazy values to see my objects when I'm using a physical camera?

For a moment I thought maybe setting the camera scale in maya might fix it, but it hasn't.

[vlado]

I'm not sure; would be best to post a scene.

Best regards,
Vlado

[tmcthree]

I'm not sure; would be best to post a scene.

Best regards,
Vlado

PhysicalScaleCameraProblem.ma.zip

Ok here's the scene.

It opens with a regular camera, if you render the sphere you can get a feel for the brightness of the scene.

Then if you select the perspective camera and check physical camera "on" you can see the extreme values needed to make the scene as bright as the non-physical camera version.

Finally, if you go to Window>Settings-Preferences>Preferences>Settings and set the unit scale for that scene to Centimetres you can see it gets extremely bright.

I would expect that a unit change wouldn't make any difference to the brightness of the scene if Vray took into account the unit scale change from Maya. Or have I misunderstood something.

[Svetlozar Draganov]

Photometric Light Scale parameter might be used to unify the illumination between different scene units:

[tmcthree]

That's what I was looking for thanks.

[Pete3d]

V-Ray will read whatever units you have set in the Maya preferences. If you want those units to be different from your render units, then this can be done with a Python post-translate callback, like this:

from vray.utils import *
p=findByType("SettingsUnitsInfo")
p[0].set("meters_scale", 1.0) # Here 1.0 is conversion factor from scene units to meters, you can change it accordingly

Best regards,
Vlado

Very good tip vlado. Worked.
Might be a good idea to have it implemented in the main Render Globals.
In our studio we pretty much always use either 1/10th scale or 1/100th.

Am I right to assume that for 1/10th scale in cm I would have to adjust your lines of code to p[0].set("meters_scale", 0.001)

thanks