Hi,
I'm having some trouble deleting points imported from a fluid sim.
I import the points and volumes that result from a flip sim, and I want to delete the points that go above a threshold. I can delete them perfectly with a simple expression, however in some random frames not only the points but also the volume primitives are deleted.
I wanted to know is this a bug? or am I doing something wrong?
I created a simple sample scene, let it sim for a few frames and inside the DELETE_ERROR node if you see the volume visualization inside the red box you'll see that the volumes go away on some frames. The desired behavior would be the one on the green box but without having to separate the volumes, delete points and merge back.
Any thoughts are appreciated, thanks.
deleting flip particles also deletes volume prims?
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- robonilla
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- eetu
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It's just a bit unfortunate but expected behaviour in your situation.
Volumes in Houdini have one point in their center, which determines their position. In your case the centroid of the volumes moves above Z=1 when the volume grows. Thus when you're deleting the particles above Z=1, you're deleting the volumes' points as well, and with them the actual volumes.
You could separate the volumes and particles into separate streams, do the deletion in the particle one, and merge back together after that. Or, you can do some creative grouping, and delete according to that, which is what I did in the accompanying .hip.
First, I make a group out of the points belonging to the volumes. Then I make a group of all the points above Z=1, and subtract the points belonging in the previous group. Now I can just delete the particle group.
Volumes in Houdini have one point in their center, which determines their position. In your case the centroid of the volumes moves above Z=1 when the volume grows. Thus when you're deleting the particles above Z=1, you're deleting the volumes' points as well, and with them the actual volumes.
You could separate the volumes and particles into separate streams, do the deletion in the particle one, and merge back together after that. Or, you can do some creative grouping, and delete according to that, which is what I did in the accompanying .hip.
First, I make a group out of the points belonging to the volumes. Then I make a group of all the points above Z=1, and subtract the points belonging in the previous group. Now I can just delete the particle group.
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- robonilla
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oh.. that makes a lot of sense.. 
It never occurred to me that the volumes had a point indicating their position, although it should have been clear when middle clicking a node with only volumes and it showed the same number of points and volumes.
Thank you very much! i'm glad I didn't send it as a bug or anything
by the way eetu… I love your lab thread! I've learned tons of Houdini just by reading and looking at your experiments!
thank you!
It never occurred to me that the volumes had a point indicating their position, although it should have been clear when middle clicking a node with only volumes and it showed the same number of points and volumes.
Thank you very much! i'm glad I didn't send it as a bug or anything
by the way eetu… I love your lab thread! I've learned tons of Houdini just by reading and looking at your experiments!
thank you!
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