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Convex Hulls


Gordon

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Yep, it should be easy esp. if you use chull. cf http://forums.odforce.net/index.php?showto...onvex&st=12

EDIT: I meant it's easy to incorporate their code. However, the algorithm is not the fastest. Actually, it might be pretty slow for huge amounts of points. But then computers are getting faster constantly anyhow. :)

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Yep, it should be easy esp. if you use chull. cf http://forums.odforce.net/index.php?showto...onvex&st=12

EDIT: I meant it's easy to incorporate their code. However, the algorithm is not the fastest. Actually, it might be pretty slow for huge amounts of points. But then computers are getting faster constantly anyhow. :)

Well my goal isn't specifically to make a convex hull sop as quickly as possible but to get used to the HDK so I'll try scratch building it :)

qhull is a pretty straightforward implementation so I'll try that one, if I can just stop screwing around long enough to write it :)

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BTW, I should mention Martian Labs has a qhull implementation for Houdini here:

http://martian-labs.com/martiantoolz/produ...?product=convex

I couldn't find any pricing info on it though. You might want to email them.

Ah, guess that nixes qhull as an algorithm then.

I didn't realise the Martian labs on was still available.

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  • 2 years later...

Not necessarily. There's always room for competing implementations. Don't let that deter you. It seems like to you their QHull SOP, you need to set up some sort of license thing at least.

So did anyone come up with anything recently? I had the Martian Labs one many years ago (we were the ones they built it for), but I couldn't get them to keep up with updates as Houdini grew. I'm pretty sure that we had it for version 4 or 5.

I just got the qhull stuff and was able to compile it for standalone, but I can't figure out how to use the qconvex library stuff to wrap it into Houdini.

Could someone tell me how to use the library?

Dave

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My last post regarding this was here:

http://forums.odforc...dpost__p__19798

As noted, I just hacked their io.c file to output a valid .ply file header. It's just slightly better than manually hacking their output for reading into Houdini.

As for some "newer" stuff, try the package here which I've header might have something useful:

http://forums.odforce.net/index.php?/topic/9119-voronoi-dynamic-location-based-fracture-wip/page__view__findpost__p__64501

(I haven't tried looking)

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If you want a *robust* convex hull implementation AND fast, then it's no trivial matter.

so then i would recommend the hull creation algorithm included in vtk if you don´t want to write your own. there are just two problems with this one. first is that it´s not too accurate and second, you have to have vtk installed what could be a bit tedious on some platforms. but regarding speed and robustness its definitely recommendable. for up to 1 mio. points it´s under 2 sec.

attached is the file with embedded otl´s, but you NEED vtk to be installed for this.

petz

hull.hip

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  • 3 months later...

I don't know how you'd do this for VTK specifically, but in general (on Windows), I just follow the regular Python package instructions but substituting "hython" instead for python. If things need to put into a the python distribution directories, then I just put it into the corresponding directory under $HFS/python instead.

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