CGTalk - Particle Collision troubles

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radcliff

03-14-2008, 07:02 PM

Greetings--

I'm working on a documentary and trying to demonstrate the "drainage basin" of a watershed. I want to mimic water running over a surface divide--on one side of the hill the water should run to a lake, and on the other side of the hill it runs to a stream. I only have Maya Complete (2008), so the fluid effects are not an option.

I've been using particles and my tests worked great. I had a cloud "rain" onto a test surface, a polyPlane, and I figured out the best settings for resilience, friction, etc. When I moved to my modeled landsurface, which was made by lofting a surface from a series of curves, the "rain" particles won't collide properly with my surface. I've tried adjusting the tesselation in the GeoConnector node, and a number of other factors, but I can't get the collisions to happen at the actual surface. They seem to be following a much, much less detailed surface.

Here are two pics: above the ground surface and below the ground surface

Thanks for your help!
Matt R

movector

03-17-2008, 09:37 AM

convert to polygon and try again
find out whether nurbs surface tesselation problem
u can post ur scene file here, let me test

radcliff

03-17-2008, 02:12 PM

Thanks, movector--

I did the Modify> Convert NURBS to Polys option, and it worked much better. I thought I had tried that before but remembered the ploy surface created was too low resolution (not enough shape to the stream bed, for instance). This time it worked OK. Not sure if I checked a different box this time, or if my memory is totally AWOL.

Still not sure why it didn't work on the NURBS version, posting the scene file here.

axiomatic

03-18-2008, 02:00 AM

I got immediate results with your scene doing the following:

open scene, run it and select some particles,
switch to the geoConnect2 node,
change Tessellation Factor to 10000 (ten thousand).
I believe that Tessellation Factor can be considered a max number of polys used for tessellation of a given object into a collision mesh. This attribute exists (and has an effect) even on polygon objects so I've always assumed that maya always tesselates a new mesh for each collision object (nCloth being the exception, which might be one of the reasons it's so awesome). Your results were probably better with the polygon object because it tessellated better after polyconversion.

I stopped at 10,000 because it was slowing down. You might want to push it higher for final render, lower for playback.

Also, you might consider using Surface Flow instead of particles and rigid body collisions for the water once it hits the ground. I think you'll find it faster and easier to control. :)

movector

03-20-2008, 06:40 AM

i have no maya 2008 installed,cant open your file,but radcliff has answered the question.
nurbs in many places just look smooth,not real,especially in this case.even when maya rendering nurbs, it will be convert to polygon internally.

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