[Sidefx-houdini-list] Closure

Mark Elendt mark at sidefx.com
Sun Jan 24 08:54:03 EST 2010


On Saturday Jan 23 at 22:37, David Johnson wrote:
> I'm actually looking for the edges. I'm writing a convex hull SOP. After I
> delete the polys that my current point can see, I need to make the triangles
> from the horizon edges back to my current point. I'm using a loop through
> all the edges of all the polys now and testing how many faces share the
> edge. If it's only 1, it's a boundary. But that is very slow.

You can look at either the GQ library or maybe GEO_PointRefArray.
Both build additional topological information.

With a GQ detail you can traverse edges to find edges that don't have
pairs (i.e. a boundary edge).

It's more work to do it with a point ref array.

> On Sat, Jan 23, 2010 at 5:34 PM, Sebastian H. Schmidt <
> sebastian.h.schmidt at googlemail.com> wrote:
> 
> > Hi Dave,
> >
> > do you want the edges or do you want  basicaly the result of a divide sop
> > does when you tick remove shared edges ?
> > if you need the divide-sop thingy you can do this here:
> >
> > GU_Detail *myFillGDP = new GU_Detail(mygdp)
> > GQ_Detail     *myFillGQP = new GQ_Detail(myFillGDP);
> > myFillGQP->boundary()
> > you might have to reverse the normals with
> > myFillGQP->reversePolys()
> > but than you can merge it back together and do a fuse with a function
> > called
> > (fast)consolidatePoints
> >
> > if you realy need the edges, ... sorry havent used that yet ;)
> >
> > cheers
> > Seb
> >
> > On Sun, Jan 24, 2010 at 12:55 AM, David Johnson <daveinengland at gmail.com
> > >wrote:
> >
> > > Can anyone explain how to use the GEO_Closure class?
> > >
> > > I'm trying to find an ordered list of the edges of the polygons that are
> > at
> > > the border of some geometry. Like if you take a polygon sphere and delete
> > > one of the polygons, I'd like to be able to find the edges of the hole
> > that
> > > is left. How can I do this? I'm trying to do it in the hdk, using
> > 10.0.430
> > >
> > > Would the GEO_Closure be able to help with this? Or can anyone else
> > explain
> > > how to do this in an efficient manner?
> > >
> > > I also sent this to support, but just in case someone is trolling the
> > > mailing list this weekend and has an idea, I'd appreciate some info.
> > >
> > > Dave
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-- 
Mark Elendt



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