[Sidefx-houdini-list] transferring data from points to volumes

Steve Gustafson sgustafso at gmail.com
Sat Apr 4 21:41:12 EDT 2009


Hey Peter. I'm not sure how you're suggestion could work.. could you
elaborate a little bit more?
The thing is, even if pciterate allows me to find the nearest points, it's
not clear to me how that would give me access to attribute data for those
points. If I'm in a standard sop vex context, I could use an importattribute
vop to pull in the attributes of the nearest N points and smooth them, but I
don't think it's possible to write data to a volume within that vex context.
Inside of a volume vex context, you can write directly to the density of the
volume, but you can't use the importattribute vop. So I'm kind of stuck with
not being able to both read in attributes and write to a volume all within
the same vex context.
This seems like the sort of thing that ought to be pretty straight-forward
in c++, so maybe I'll try my hand at that.

On Fri, Apr 3, 2009 at 9:53 PM, Peter Bowmar <pbowmar at gmail.com> wrote:

> I haven't tried this, but a pciterate() should work, basically each
> volume sample would find the nearest point(s). This would need
> VOPs/VEX of course but would be much faster than an expression. I
> don't think you'd need a Volume VOP, but again I haven't actually
> tried this.
>
> Cheers,
>
> Peter B
>
> 2009/4/3 Steve Gustafson <sgustafso at gmail.com>:
> > Hey everyone. I'm trying to figure out how to transfer attributes from
> > points to volumes. Something like the volume_sample VOP, only the reverse
> of
> > the process: a smooth, weighted lookup of the value of an attribute for
> the
> > particles found within each voxel. Anyone know of any good tricks to do
> > this?
> >
> > The only approach I'm seeing atm is to use an expression inside of a
> > volumemix sop. You could pregenerate a 3d grid of points, each point
> > centered within the respective voxel, so that this would be a reasonably
> > cheap process (the smoothing of data would be optimized through normal
> sop
> > procedures. I.e., a weighted attribute). But it still requires an
> expression
> > to be executed against each voxel, which obviously doesn't make for the
> best
> > approach. Ideally, there'd be a way of access the data from within a
> volume
> > vop.
> >
> > Thanks
> >
> > ps - I'm currently in H9.5
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