When “Use V-Ray Instancing” is checked, the velocity channel in the render element doesn’t properly render.
I tried testing this, and neither an animated sphere, nor the original PFlow’s geometry particles affected the VRayVelocity render element. I might be missing something obvious. In other words, Frost wasn’t the exception, it just rendered like every other object, without a Velocity channel render element data…
Also, which version of V-Ray are you running?
Are you rendering with a VrayMtl or a Standard. Sometimes the data channels get wonky with a weird mat and the “simple” tests break because you forget to use a real mat.
There was no material whatsoever on the Frost, but assigning a VRay material to Frost did not change anything.
Then I realized I was running an old 3.33.04 build (from before I went away for two months to the home country of V-Ray).
So I installed a newer build, and the sphere and blob Frost started generating velocities, but V-Ray instances did not.
So now I have officially reproduced the problem. 
I will log it, but Paul is on vacation for 10 more days, so it might take a white before this gets fixed.
From my calculations, Paul should be back now. Can I get an ETA on this fix? I have a render ready and if it’s a 1-2 days I’ll hold on. Otherwise I’ll move forward.
I’m hoping this will be an easy fix, and I’ll have a build ready for you to test tomorrow. I’ll let you know if I run into trouble.
Got the update! Thanks!!
I’m having an issue when using a PRT as a source with veloicyt. A pflow renders the channels fine, but when I load this prt I get these results:
Would it be possible for you to please send us a 3ds Max scene file and a PRT file that reproduces this problem? (I only did some simple tests, but I didn’t notice any difference between PFlow and PRT sources.)
Here’s a simple scene I couldn’t get any velocity RE out of.
Also with this file–when I uncheck Vray instancing under Frost it pings my memory to 100% and locks up which shouldn’t happen with one particle of a teapot.
Frost_2_11_velocityError.zip (84.6 KB)
Here’s the PRT scene. I’ve linked the .prt from my google drive. I don’t know if these two bugs are related.
drive.google.com/open?id=0ByYx2 … 1dNX2Z5Y3M
Frost_2_11_velocitySample.zip (249 KB)
Thanks!
For the simple scene you posted: the one thing I noticed is a difference between the render particle count (1000000) and the viewport particle count (1). After changing the render particle count to 1, it worked as expected for me.
For the PRT scene: I changed the PRT Loader to render 1% of the total particles, and then I rendered with “Use V-Ray Instancing” on and off. I got the same result in both cases, so it’s not clear to me what the problem is. What do you expect to see here? Is there perhaps a problem with the Velocity channel values in the PRT file?
Both times the viewport % vs rendering % was fooling me. DOH! Thanks again for the quick fix.
Alright, thank you for letting us know!