how to get vray velocity render element

[ttdww]

Hi guy,

How would I get a Vray velocity render element for water, drops, foam? The sim was run with velocity channel and Vray motion blur works properly however I'm not seeing how to get a correct velocity element. I've used it before with After Effects and Reel Smart Motion Vectors to get correct motion blur in post both with geometry and also another fluid sim plugin (cough cough - no names mentioned). Looking for the method/settings for creating it correctly with PFD. Thanks!

[ttdww]

I've noticed that the velocity element works correctly when I also render with Vray motion blur turned on in the renderer. In this case it defeats the purpose since we're trying to save on render time by not rendering with Vray motion blur and adding it in post with the velocity element.

[Ivaylo Katev]

you have to export the velocity channel (for the grid and the particles)
the liquid velocity is obtained automatically
for the foam/splash velocity you need to put the foam shader in geometry mode, the atmospheres can't produce velocity render element. the bad thing here is that the geometry mode can't produce analytic scattering

[ttdww]

Hi Ivaylo,

Thanks very much. I should have noted that - the liquid was working correctly however not the splashes/foam.

With that said, I had the settings you outlined set up correctly however it still wasn't working, until... possibly a breakthrough! To get the velocity element to work but with Vray's render panel mblur set to 'off' I had to set the PHXfoam shader's motion blur mode from 'by vray' to 'force on'. Maybe this means: use the velocity channel info for rendering even if not active by Vray? Thanks again!

[Ivaylo Katev]

well, i didn't understand that your goal is just the motion blur, you asked for velocity render element, and the only way to have it is to use geometry mode. however motion blur you have in atmosphere mode too, even without vray .

[ttdww]

No problem Ivaylo. I could have included more detailed info. Here was the goal:

--We are running out of ram rendering a splash shot with motion blur (beyond 32GB of ram on these nodes).
--Therefore we wanted to add the motion blur in post using a velocity render element from Vray
--At first we weren't able to get the RGB data showing up for the foam/splash drops - it was just rendering black
--To solve it we needed to set the PHXfoam shader's motion blur mode from 'by vray' to 'force on', so Vray would generate the RGB data to be included in the element but with motion blur deactivated in the Vray render panel.
--It's working great.

That's good to know about the atmosphere mode as well - I'm sure we'll need to utilize that in the future.

Thanks very much again.