Nparticles Instancing Strange Rotations and Displacements

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Old 04 April 2013   #1
Nparticles Instancing Strange Rotations and Displacements

I am running into some frustration with Maya NParticles, and would be very grateful for some help

So I created an NParticles emitter (water), placed it inside a mesh, set the mesh to nmesh > create passive collider.



So far, so good. Now I want to instance it, so I create a particle instance made from this default scaled pyramid primitive.
In the NParticles rotation options, I check 'compute rotations' and in the collision properties I also check 'self collide'. In the instancing options, I check 'allow all data types' and then set rotation type to RotationPP and rotation to RotationPP.

As expected, the pyramids start to collide with themselves within the volume.



Modifying the pyramids a bit and re-simming seems to work just fine. However, I now want to substitute the pyramids with grains of rice (I am modeling some sushi).

Then it goes nuts!



I find that if I remove 'RotationPP' from the NParticles Instancer Rotation parameter, it doesn't go nuts anymore but instead there is a displacement away from the passive collider.



I have no idea what is going wrong. I tried scaling up the model, freezing transformations on everything and deleting history, but nothing seems to work. I tried instancing simple UV spheres but as soon as I deform them, they behave just like the rice grains again.

When I decrease the particle radius, I observe that the particles are being emitted as if the particle emitter was misplaced somehow, and there is some kind of numerical blow-up.



I then realized that I forgot to clear transformations on my emitter, but now it just offsets at a new location.



Any suggestions?

Thanks...
 
Old 04 April 2013   #2
Your rice mesh must have an offset in the vertex positions away from zero. After setting the instancer to use the rice, select all the vertices on your original rice mesh and translate it until all the instances overlap the particles. (there are other ways but this should be relatively foolproof)
 
Old 04 April 2013   #3
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