pflow mblur SP2

[kimgar]

hi!

sorry for being outrageously close to crossposting here. i realize there are numerous threads on pflow and motionblur, but i just couldn't find any straight answers to whether the issues regarding pflow/mblur has been solved in SP2? (i'm not even sure i'm having 'issues', or if the behaviour is expected...)

as far as i understand i need to keep all geometry in the scene at all times, and no changing mesh topology. i'm no pflow expert and haven't even used mblur before, but i've tried my best to keep particles from spawning/dying, but i'm still getting the results below:

what i'm trying to render:


what i get:


...and the pflow:


...i sort of see what is going on here, looks i need more mblur sampling or something, but i have no idea how to go about it - any ideas?

[vlado]

You need to increase the "Geometry samples" parameter for the motion blur from the V-Ray settings in the Render scene dialog,

as far as i understand i need to keep all geometry in the scene at all times, and no changing mesh topology.

This is not necessary for Particle Flow objects; V-Ray will treat them specially from other geometries so no problem if particle counts are different between frames.

Best regards,
Vlado

[joconnell]

More particle flow integration steps too.

[kimgar]

fantastic! i found the geometry samples and upped it to 16, and this is more like it! wonderful! thanks vlado!



...and thanks for the tip on integration steps joconnel! it won't really impact motionblur directly will it? but it's a good thing to keep in mind if things are going to move fast, or if weird behaviours occur, thanks!

heh, while i'm at it - any tricks i could pull to reduce some of the noise without upping the sampling subdivs to much? currently both geometry and mblur samples are at 16 with adaptive dmc image filtering. guess i could just do a post blur, but i'm just being curious

[joconnell]

fantastic! i found the geometry samples and upped it to 16, and this is more like it! wonderful! thanks vlado!



...and thanks for the tip on integration steps joconnel! it won't really impact motionblur directly will it? but it's a good thing to keep in mind if things are going to move fast, or if weird behaviours occur, thanks!

Yep - vray feeds of sub samples of the objects transformations - for a normal max object moving it's easy since vray can just look at the trajectory of the object in its function curve and sub sample as much as it needs. In particle flow it isn't a continuous trajectory like that, it's calculated at whatever rate you specifiy with the integration step to keep memory overheads down. Because of this even if you have vray set to 16 motion blur samples, if particle flow is only set to an integration step of frame or half frame, vray can only motion blur the particle at 2 or three positions since theat's the limit of the values it's getting fed.

Again you don't always need to do this unless you have some very fast moving particles where you'd like to see nice streaky highlights. Another place would be if you were using particles as a swarm - say if you had an animated bee as a particle where its wings flap up and down within a frame you'd probably need three or four particle flow samples (1/4 frame) and 4 vray geometry samples to be ableto get a nicely blurred arc on the wings.

The two are very heavily tied together and it can make for some fairly memory intensive renders - I've had renders where I was using a coke bottle as a particle (maybe a few thousand polys per particle) and using maybe 1500 particles as a swarm with motion blur. The vray frames were really nasty to render and half of that was particle flow calculating - quite often it'd crash for memory reasons. I started baking the particle movement to nulls and attaching an instance of the bottle to the nulls instead and things dropped back to 2 - 3 minutes a frame. It can get a tad nasty

Noise wise I'd have a look at the particles on the move - you mightn't notice the noise at all.

[kimgar]

thanks alot for the great explanations joconnel, it makes perfect sense now
good tip on the coke bottle instancing too! i'll remember that one when i come across large setups in the future.