[Sidefx-houdini-list] overlapping point instance volume density pop

Tom Nixon ignivomous at gmail.com
Wed May 31 12:24:39 EDT 2017


Thanks, Dan and Mark,
Thanks for your suggestions!

Mark -
I hope to get some time to test your theory today - and I'll see about
getting a simple setup to pass along.

Dan -
Your assumptions are correct.

I'm afraid I'm instancing-it-up (thousands indeed), and combining them
would be a last resort for this reason. So far, I've been relatively
fortunate, and have been able to reduce most pops in comp, but I am hoping
to learn how to resolve this before I encounter a case that I can not
resolve so easily.

I will hopefully get a window to try your suggestion of using Houdini
Volumes instead. I had an early iteration that used Houdini volumes, and I
want to say that I saw this behavior then as well, but I'm not confident of
that, so will have to do a test to confirm.

Cheers!
Tom

On Wed, May 31, 2017 at 4:41 AM, Dan Wills <gdanzo at gmail.com> wrote:

> G'day Tom,
>
> I've inferred that you're rendering in Mantra (afaik the only thing working
> with Packed Disk Primitive (though, I could easily be wrong about that))..
> and how are your VDBs being shaded?
>
> I've also seen rendering issues with multiple VDBs overlapping. Not
> entirely sure that what I saw matches exactly with the problems you're
> seeing Tom, but if you /are/ rendering VDB volumes, perhaps you could try
> converting to Houdini Volume Primitives instead? (VDB Convert Sop).
>
> I guess merging them all into one VDB is not an option? VDB *is* quite good
> at this!
> If you were *really* instancing-it-up before (thousands of copies of 5
> things or something), then.. that's probably not a good option.
> But, if there's only a few and you can just merge 'em all into one VDB..
> then that nicely works around rendering overlapping VDBs any more (as long
> as its then the only one in the render), and still renders using a VDB
> file! (no format-change to bgeo) ;D.
>
> Best of luck!
> Dan
>
> On Tue, May 30, 2017 at 6:15 PM, Olivier Jeannel <facialdeluxe at gmail.com>
> wrote:
>
> > I had some vdb problems when in vop I setted the density going to values
> > greater than 1.
> >
> >
> > On Tuesday, May 30, 2017, Tom Nixon <ignivomous at gmail.com> wrote:
> >
> > > Hi Francois,
> > >
> > > I'm afraid I'm seeing something more than just a sum of two densities.
> > The
> > > issue is that there is a visible change in the form of a "pop" between
> > two
> > > density levels. This is not apparent when isolating the individual
> volume
> > > instances.
> > >
> > > This is to say a region of the render appears to drop or increase in
> > > density from one frame to the next. When each instance is rendered
> alone,
> > > the pop does not happen.
> > >
> > > Unfortunately, rendering each volume individually is not a viable
> > solution
> > > to my problem.
> > >
> > > Thanks
> > >
> > > On Mon, May 29, 2017 at 6:58 PM, François Duchesneau <
> houdini at trinix.ca
> > > <javascript:;>>
> > > wrote:
> > >
> > > > Hi Tom,
> > > >
> > > > It's normal to have an increase of density when two volumes overlap.
> > You
> > > > can reproduce it by rendering two volume sphere overlapping a little
> > bit.
> > > > Are you referring to something else?
> > > >
> > > > Francois
> > > >
> > > >
> > > > On 05/29/2017 07:04 PM, Tom Nixon wrote:
> > > >
> > > >> Hey everyone,
> > > >>
> > > >> I'm getting a result in my renders that I'm don't fully understand
> > yet.
> > > I
> > > >> hope one or some of you have come across this and can shed some
> light
> > on
> > > >> it.
> > > >>
> > > >> I have a number of volumes that are being instanced as packed disk
> > > >> primitives in my renders. The density appears to pop up and down a
> > > couple
> > > >> times through the frame range.
> > > >>
> > > >> When I isolate each volume and render it, I am unable to see the
> same
> > > pop
> > > >> in the renders.
> > > >>
> > > >> It appears that the pop is a result of the overlapping volumes, as
> > when
> > > I
> > > >> offset the points to reduce the overlapping and render them
> together,
> > > the
> > > >> pop appears to disappear.
> > > >>
> > > >> If anyone has any experience with this, I'd appreciate your input!
> > > >>
> > > >> Thanks,
> > > >> Tom
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