[Sidefx-houdini-list] Fluid Source Sop creating inverted levelsets

Vincent Fortin vfortin at gmail.com
Wed Dec 5 16:55:07 EST 2012


I'm surprised you've managed to use a normal sdf for collisions though. For
me it doesn't work. It all boils down to how the rig is built, collision
detection shares nodes with sourcing which relies on positive values to
generate the mask. Surely there are other reasons. I'd like to know too!



On Wed, Dec 5, 2012 at 2:00 AM, Nicolas Delbecq <nico.delbecq at gmail.com>wrote:

> I understand that. If you invert the levelset from the fluid source sop (so
> you have a normal one) you can still use it as a collision in dops as long
> as your source volume dop has its source volume parm set to minimum,
> instead of the default maximum.
>
> What I don't get is why sideFx has chosen to use inverted levelsets by
> default where actually they could have set it to use normal levelsets. I
> would be curious to know the reason...
>
> On Wed, Dec 5, 2012 at 8:35 AM, Vincent Fortin <vfortin at gmail.com> wrote:
>
> > If you go in the Container Settings tab and switch between the different
> > modes, you'll notice that the volumes settings change. Source Smoke will
> > generate a simple volume, Source Flip will generate a SDF, whereas
> > Collision will generate an inverted SDF by automatically UNCHECKING the
> > invert option for you. Don't worry, you're a sane person in an insane
> > world.
> > At least the documentation has 1 mention about it:
> > "Some fluid operations (such as collisions) expect negative border
> > conditions to work properly."
> > Now that it all makes sense, you can go and vop-negate the values inside
> > the volume and effectively reuse your SDF's for other things. As long as
> > you take care of the name bindings... but that's a different story I
> guess
> > :-)
> >
> >
> >
> >
> > On Thu, Nov 29, 2012 at 9:19 AM, jacob clark <jclark2900 at gmail.com>
> wrote:
> >
> > > Hey Nico,
> > >
> > >  It is quite strange! Luckily we've managed to work around the
> > strangeness
> > > so far in our pipe. But if anyone knows, I also would love to know what
> > the
> > > benefit is for inverted level sets.
> > >
> > > cheers,
> > > -j
> > >
> > >
> > >
> > > On Thu, Nov 29, 2012 at 9:08 AM, Nicolas Delbecq <
> nico.delbecq at gmail.com
> > > >wrote:
> > >
> > > > Hi,
> > > >
> > > > I've noticed that the fluid source sop was creating collision
> levelsets
> > > > being positive inside the volume and negative outside. By default the
> > dop
> > > > source node is reading that correctly.
> > > >
> > > > This is an issue because when your pipe relies on levelset for other
> > > > operations you can't use directly the ones created from the fluid
> > source
> > > > sop.
> > > >
> > > > Do anyone knows what's the reason for that ? Seems quite strange no ?
> > > >
> > > >
> > > > Cheers,
> > > > Nico
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