topic Re: Caustics / System Unit Query in 3ds Max Shading, Lighting and Rendering Forum

Caustics / System Unit Query

ah254 — Thu, 02 Apr 2015 13:17:14 GMT

How do caustics respond to system units? I was using max in inches but I'm now modelling a brand new scene in mm and it seems impossible to get caustics to show up regardless of any setting. Any ideas anyone?

Thanks

Adam

Re: Caustics / System Unit Query

CAMedeck — Thu, 02 Apr 2015 13:38:16 GMT

Make sure your System Units are changed to mm, and not just your Display Units. The renderer should understand the units being used, and scale things accordingly. Are your objects correctly scaled for the environment?

Re: Caustics / System Unit Query

ah254 — Thu, 02 Apr 2015 17:41:29 GMT

Yes both my display and system units are now mm. Material is physical glass. I've attached one model of a larger object from when I used inches and a smaller object now that I'm using mm as system units. With identical settings the caustics only generated in inch model. Even with the caustic photons bumped right up to 90 million it failed to generate, think I'm missing something but have no idea what it could be! How might I go about checking my objects are correctly scaled for the environment?

Thanks

Adam

Re: Caustics / System Unit Query

CAMedeck — Thu, 02 Apr 2015 17:56:20 GMT

You've got one small scene (mm) and one large scene (inches). Of course the lighting and caustics will behave differently since the light is traveling so much further.

Is it intentional to have one scene so much larger than the other?

Re: Caustics / System Unit Query

ah254 — Thu, 02 Apr 2015 19:01:13 GMT

Yes I've been playing around with how scale effects it, with the smaller model (mm) it seems impossible to have the caustics show up at all. What setting is best to play around with? I think I've tried most things but nothing seems to happen.

Adam

Re: Caustics / System Unit Query

PROH — Thu, 02 Apr 2015 21:53:27 GMT

Photometric light behave according to the scale. So if you want real world realism, you objects should be scaled "real". A glass vase being 4,5 meters high, isn't something I see everyday, and it will of course create a different caustic effect than a vase being 35 cm high.

It's your choice wether or not to follow these guidelines, but don't compare to such different setup.

Re: Caustics / System Unit Query

ah254 — Thu, 02 Apr 2015 22:23:05 GMT

It doesn't have to be a vase, it could be anything, sculpture etc. I've just been trying to figure out how the settings should be amended according to different scales. It was actually the 4.5m model that generated the caustics strangely enough. I would have thought it would be more difficult to generate caustics on larger objects given the extra distances. I will keep testing through and amend the photometric settings for the smaller model.

Thanks

Adam

Re: Caustics / System Unit Query

ah254 — Thu, 02 Apr 2015 23:01:34 GMT

Ok think I've figured it out! Just had to drastically increase energy from photometric light and then adjust exposure. Thanks for your assistance!

Adam