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. http://fx-td.com/content/misc/recursive_growth_v2.hiplc Many thanks!