Volume Advection

[sipi]

Hey everyone,

I'm advecting this density field with the velocity field using a for loop, and if I crank up the iteration the density starts to clip.

Do you have any idea how to prevent that?

volume_advection_clipping.hiplc

[ryew]

You can expand your bounds with a VDB Activate SOP in the "Expand" tab, but I believe the actual issue is not clipping but rather that your velocity data stops at the bounds your input frame is frozen on so your loop is multiplying by 0 in those areas - you might need to pipe in velocities from later frames or fake some by creating a custom velocity field

[sipi]

11 hours ago, ryew said:

You can expand your bounds with a VDB Activate SOP in the "Expand" tab, but I believe the actual issue is not clipping but rather that your velocity data stops at the bounds your input frame is frozen on so your loop is multiplying by 0 in those areas - you might need to pipe in velocities from later frames or fake some by creating a custom velocity field

Thank you! I think I will go to the direction of using velocities from later frames somehow, because I have no idea how to create a custom velocity field which expands outward with keeping the border values.

Actually there is an other solution which is to resimulate the sim with greater padding value, but the sim could become different so I purposely avoid this option, I want to do it all in post witout resim.