PFlow, VRay, and big bounding boxes.

[Valtiel]

I've recently encountered a strange issue with V-Ray, Particleflow, and the "scene bounding box is too large..." warning. I understand the nature of the message: some (visible or hidden) objects in the scene are placed too far from the scene's origin and could cause raytracing issues. What makes it strange is the inconsistency at which this message occurs in my scene.

 

The scene uses Max Design 2011 64-bit and all objects are no further than 800 system units from the scene origin and everything is contained in an enclosed light-grey "studio" shell. In production renders of previous iterations of the scene this warning would pop up on some frames but not others. What I first thought is maybe some particles are escaping the deletion conditions/events in my particle logic, but unhiding everything and ensuring all particles are visible yielded nothing outside the studio object.

 

It hasn't actually caused problems until today. I'm about to send the latest version off to a render farm and started running a low-res test render on my machine beforehand. On about the 108th frame it gave the message and essentially got stuck on the light-cache pass. I didn't let it finish but it was estimating over 2 hrs on that pass when I hit cancel. These tiny 480x270 test frames were otherwise taking 25 seconds apiece to fully render with IR/LC before this frame.

 

What's stranger still is I went back to the save file of the same scene with production render settings, nothing else is different, and tried rendering the same frame and it works fine along with a few other random frames in the suspect time segment. I'd have expected those settings to be independent of the bounding box issue or at least more likely to cause it at higher quality settings if anything. I haven't tested every frame but so far it seems fine; no warning. I am quite concerned that it will drag out the time and cost at the farm if it does happen.

 

Interestingly it would also come up if I increased the dynamic memory limit from 800MB in the settings:system rollout so I don't touch that anymore.

 

So it's happening in some frames but not others in a scene that apparently doesn't change maximum dimensions, and appears when render settings are lower or memory limits are higher against intuition. Is anyone here familiar with this warning and why it might be behaving the way it is for me?

[Scott Schroeder]

You are getting that error because you are indeed having particles escaping. You might not think it, but Vray is telling you otherwise. Do you tend to get the error in the later frame numbers? If so, then I suspect you have particles that are living beyond their needed time and are just floating out into space.

 

What are your system units? Miles? Feet? Inches? Light Years? How are you deleting your particles once you are done with them? Are you using a deleting object or deleting over time? What are you using particles for?

 

You need to provide more information as to what you are exactly doing with your particles.

[Valtiel]

Hi Scott.

 

In the case of the low res render, the warning's coming quite early. In general, though, it occurs on and off throughout an animation. The warning goes away often several frames after it appears.

 

The particles represent a effluent of drilling fluid returning from a rig (dirty oilsands hardware) and being sifted/separated through a shale shaker and centrifuge setup. They are mostly deleted with age tests, and none of the age limits are terribly high for the particles still in motion. Some are intended to represent a fluid material piling up on the floor and are allowed to persist but not without having their speed checked. Those that are still moving after they should have collided with the floor are given an age-based deletion event.

 

My system units are inches with a 1:1 with generic display units, so the total diameter of the "studio" object is no larger than 1600" and zoom extents all doesn't go much farther beyond it with everything unhidden and 100% of the particles displayed in viewport from any orthographic point of view, even at the frames where the warning is reported.

[Tommy L]

can you put a kill by distance on the particles?

[Scott Schroeder]

How big is your floor deleting object? You may have a rascally particle that gets away from the floor and can't be tested by your speed/age test, since it may not have actually collided with the testing object.

 

When using particles, I usually put a super kill object that is 2-3 times the size of say the floor. This ensures you are trapping any and all particles.

 

Try changing your particles to something noticeable, like giant teapots, and see if anything is getting away from your events.

[Valtiel]

Tom: I'm away from my workstation at the moment but I'll check PFlow (3ds2011) when I get home. Off-had, I don't think PFlow tracks distance travelled from the beginning of an event, thought.

 

Scott: The whole containing environment (1600units diameter, 400 units at the highest point) is the collision object but it's paper-thin with it's normals flipped inward. When building the scene I noticed some particles clipping through it so I put a contingency age test below the collision test to ensure any particles that haven't tested positive for collision well after they reasonably should have will be killed. So any that get through don't live long after and aren't travelling very fast (~30inches/sec). Those that do collide have their speed set low and a second contingency speed test removes any that are still moving slowly afterward. I'll try the teapot thing though just in case some are escaping a mistake in the age-trapping logic.

 

I also posted about this at the Chaos Group forums. Vlado responded (one of the chaos group guys) that there's a known issue in Maya V-Ray that can send particles flying off into space at unreasonable speeds, and thus distances, and cannot be tracked in the viewport. I sent him a copy of my scene file to see if he can reproduce the problem.