System Units - again

[digitarch]

never understood it completely and still can´t find an "final" answer to me when searching the forum:

As i find in Vlados Demoscenes the 3dsmax system units set to Meter (default=inches?!) and in the vray helpfiles like at physical camera mentioned "Focal length ... This setting takes into account the system units configuration to produce the correct result..."

is it MANDATORY within vray to set the max system units to Meter?

Several Plugins and other 3d-software had problems when system units not set to default inches, also the scaling when importing meshes is a problem as most people seems to keep the system units to inch.

So what to do best when assuming i want the optimum in vray - meter system units or keeping the default?

Matthias

[vlado]

It is not necessary to have the 3ds Max system units set to meters.

What is meant in the V-Ray documentation, is that the focal length is always specified in millimeters, but V-Ray will take care of converting this internally to the current scene units.

Best regards,
Vlado

[digitarch]

well, its not only the camerasettings, but also the discussion on lights, bouncing, bleeding... and their relation to units - should we stay to inches or better switch to meters?

[vlado]

There is no "better" units settings; you should be able to work successfully with whatever units you need.

Light bouncing and color bleeding do not depend on the scale of your scene; for light units, the lights themselves (both V-Ray and photometric lights) take care of converting the input values properly as needed.

Best regards,
Vlado

[andrewjohn81]

just figure out what units best works for you and NEVER change it.

For us, we use Millimeters for system units because that's what the engineers in the company use for ProE. That way if I import something it's the correct scale.

The reason I say never change it is because if you have a scene, say in inches, and it has groups, or things linked, or skinned, etc. then when max imports that scene it will be all F'd up. There are many attributes that don't translate properly between difference scene units.

For that reason it is a good idea just to keep one. If you work with drafters, figure out what their files are in. Instead of asking them, just import something you know the size of and measure it. If it's right, then you're set. If it's way small or way big, then use a different system units.
that'd just be my recommendation though. I'm sure some of the other folks here might disagree for some, hopefully valid, reason.

[NOSIDE_SARL]

Hi everyone,

I have a scene in maya, which is Huge, something like 50km large.

I can't set my scene unit to meters because vray will result with a "Raycaster ERROR" due to "too large scene Bounding box".

So I went back to "cm" unit, and assumed that 1cm = 1m. So now, I need to ajust VRay properly, and divide the scale of my lights /100.

By default, the Photometric lights scale is 20 (and I heard that VRay default unit is cm). Should I put the value to "20/100 = 0.2" to tell VRay that 1cm = 1m ?

Thank you

[vlado]

I can't set my scene unit to meters because vray will result with a "Raycaster ERROR" due to "too large scene Bounding box".

This is just a warning, not an error. In most cases, you can simply ignore it - things render fine anyways.

By default, the Photometric lights scale is 20 (and I heard that VRay default unit is cm). Should I put the value to "20/100 = 0.2" to tell VRay that 1cm = 1m ?

V-Ray doesn't have a default unit - it just takes what's written in the Maya preferences. The photometric units only matter if you use V-Ray lights with physical intensity units (lumen etc), IES lights or the V-Ray sun/sky. Also, if you are using a physical camera, then you don't need to adjust the photometric scale, since the physical camera will take care of that.

If you do need to change the units that V-Ray uses internally, you can use a post-translate Python callbacks script, as described here: http://www.chaosgroup.com/forums/vbu...250#post452250

Best regards,
Vlado

[NOSIDE_SARL]

thanks a lot vlado,

working fine

[chriserskine]

I normally work in meters, though sometimes km's or mm.

I find converting between these to be no problem. I can have a master file set in meters, and xref either mm, km scenes into it without issue. (unless you are using biped)

but as soon as its between inches and meters. seem to get a lot of problems.

[3DMK]

The best scene units to use is the one that has the most relevance to the size of the scene.

If you're doing a large city - use KM's

If your doing a residential development - use m's

If your doing an internal - use cm's

If your doing closeups - use mm's

Hope this helps

PS. When will America come out of the dark ages & start using a decimal system instead of the dead & extremely painfull imperial one???? I pity you guys that work in America.

[greysheep5]

what i stumbled upon last week was that the correct display of the lights in the viewport actually depends on the scale...

back then, as i installed a new 3dsmax copy on one of our machines, which was set to the default system units in inch and generic display units, i saw, for the first time, the (vray)lights react in the viewport nearly the same in intensity as when rendered! why is that vlado??? a real bummer that it changes when you set system to cm and display units too, which is the way we normally work.

i mean we have no problems with the lightning, and we are used to lights in the viewport being totally overexposed (never got all that viewport exposure stuff working), but that was an eye opener. would love to work this way with inch/generic, but that´s no alternative as we are dealing mostly with architectural stuff and external files most of the time set to meters or cm.

with best regards,

christoph.