extreme long renders for Nparticles

[R_Cyph]

I'm currently trying to render a 300 frame cached instanced nparticle sequence. near the beginning of the range it renders fairly quick 1-2 minutes the further into the range the render gets stuck the "compiling geometry" phase for 30-60 min before rendering the frame which only takes a few minutes. at peak there is only a few 100,000 particles and the instanced geo is only a few quads per particle.

[vlado]

Which build of V-Ray is this? Do you have motion blur enabled? Can you get us a scene for this?

Best regards,
Vlado

[R_Cyph]

here is a stripped down scene.

Yes i'm using motionblur. we're using vray for maya 2011 x64 1.5 sp1 standalone ( although this happens if I render in maya as well )

After 100 frames or so a few different things happen at random

1) when cached or uncached the particles seem to render fine for the first 100 frames or so. After that I get a compiling geometry hang for a long time at which point it renders as I stated before.
or
2) does not render the particle instances at all.

[R_Cyph]

Vlado,

Did you get a chance to look at this yet?

[R_Cyph]

vlado? a lil help

[ivaylo.ivanov]

Hello R_Cyph,
I think the problem is with the bounding box of the scene. Because of the scale of the scene, the field and the lifespan of the particles, the bounding box gets huge probably causing problems with the raycaseter. Yo can try decreasing the lifespan and scale down the simulation until you stop getting this message (or start working as expected):
// Warning: Scene bounding box is too large, possible raycast errors.

[R_Cyph]

I'm not sure thats possible with our pipeline as all our assets are to realworld scale in centimetres. Is there no way around this? it renders fine in mental ray or scanline.

[vlado]

I don't think the bounding box is the problem, but I'm still looking into it. For the moment, it looks like some bad geometry...

Best regards,
Vlado

[vlado]

So, after some more debugging, it looks like Maya gives some garbage info about the particles (positions, velocity etc)... perhaps the particles with this data are not valid, and I'm looking for ways to find out if they are or not...

Best regards,
Vlado

[R_Cyph]

Alright let me know if there anthing I can do.

[ivaylo.ivanov]

We got an answer from Autodesk, and the only official way to fix such problems seems to be to add a collision geometry to destroy particles that go too far away and artificially are growing the overall bounding box of the system. As I understand, this do not works always for particles that are moving with huge velocities. We can try to add an option to detect these particles, but must give it a thought how this can be implemented.

[R_Cyph]

Did you try this with my scene already?

[R_Cyph]

SOLVED

I found the issue. I had an expression on my mass channel which resulted in some particles having an extremely low mass. This caused some particles to fly out into scene space causing an extremely large bounding box. Since these instanced particles flew out into space so quickly they didn't show up in render or in viewport. I changed my mass channel expression to always have at least 0.1 mass and this seems to have solved the problem.

[R_Cyph]

Thanks all the help.

[vlado]

Heh, ok - good to know

Best regards,
Vlado