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Collision surface for VDB advection

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Hey folks! 

I was hoping to gain some understanding on how I might 'mask' out areas from the advection process. I have a recursive growth setup and want to add some objects into the scene where the growth will react to and grow around it...

Im not sure the best way to go about this so im not subtracting the colision surface from the growth vdb every frame... ideally some vops setup to multiply the negative space of the collision geo with the direction of growth (velocity) so that it zeros out as it nears the surface.

Im using a modified version of this setup i found on the forum. attached youll see the surface i want a collision with.


Many thanks!


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I managed to sort of get this working by creating a velocity volume of the collision geo and adding it to the noise velocity volume that is being used to drive the random growth.

i dont love this solution as i dont fully get to control how close the tolerance is to the actual surface geo. id like for it to get very close but not intersect. if you can thing of a better way to do this id love to hear it.


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ok, just to follow up on this topic for anyone wondering.

I figured that the resolution of the velocity field needed to be higher (smaller divisions) if you want to reduce the sample distance... which those changes you can have a might tighter tolerance to the collision geometry! 

pretty happy with this setup after making those changes.


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