Edges to Curve?

Forums Houdini Learning Materials Edges to Curve?

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anon_user_21411066: Member; 210 posts; Joined: Jan. 2014; Offline

April 7, 2014 7:05 p.m.

In this thread I would like to address two concerns.

1. How can I convert the edges of an object to curves?
I've a thread where this was discussed before but that didn't help.

2. Why doesn't Houdini handle edges properly? Edges are always refered as the connection between two points like p0-1, p11-12 and so. Why doesn't edges have their own index like p0-1 = 0, p1-2 = 1, p2-3 = 2 and so on?


eetu: Member; 606 posts; Joined: May 2007; Offline

April 8, 2014 4:32 a.m.

1) Convert SOP, Ends SOP, Wireframe SOP and Polywire SOP are your friends in this sort of trickery. Check the attached for a couple of examples, I'm sure there are many more ways to do these things.
Also check out the hip file in this post, http://forums.odforce.net/topic/8471-eetus-lab/?p=102777 [forums.odforce.net] for something along those lines.

2) This has bothered me bit for a long time, and I'm sure many others. Although I guess in some situations the “directed edges” we now have might be better, but I'd sure like to have edges as first class citizens. Think edge attributes..

At least edges can be grouped with the Group node these days, it makes things a bit better.

Attachments:
ee_edgecurves.hip (64.5 KB)


anon_user_21411066: Member; 210 posts; Joined: Jan. 2014; Offline

April 8, 2014 8:38 a.m.

First of all thanks, this is my feedback:
Convert SOP doesn't work at all.
Ends SOP doesn't work either.
Wireframe SOP works in a way but is very limited. In this case it conviniently does right what I want, it gives me round surface along the meshs edges but if I want the edges/curves for a different purpose, let's say sweeping a custom cross section along these curves, I couldn't.
Polywire is quite similar except the mesh it gives me looks messy.

The grouping of edges doesn't work as well respectively it doesn't work well.
You can indeed group for operations like crease SOP but it doesn't work for extracting edges for a sweep, or am I missing something?


eetu: Member; 606 posts; Joined: May 2007; Offline

April 8, 2014 8:53 a.m.

Korny Klown2
First of all thanks, this is my feedback:
Convert SOP doesn't work at all.
Ends SOP doesn't work either.

if I want the edges/curves for a different purpose, let's say sweeping a custom cross section along these curves, I couldn't.

Please define “does not work at all” a bit clearer, so we can help you achieve your goal.

When I just add a Sweep SOP after the Convert SOP in the hip I gave you, I get this:

Attachments:
ee_edgecurves02.hip (72.1 KB)
ee_edgecurves02.jpg (353.6 KB)


anon_user_21411066: Member; 210 posts; Joined: Jan. 2014; Offline

April 8, 2014 9:46 a.m.

Ok, with “doesn't work at all” I meant that after appending the convert SOP and seeing no changes I assumed that nothing happend, so this far I admit it is a missunderstanding between me and the visual feedback. However even if append a sweep SOP, it doesn't work.

The convert SOP is set from “All Types” to “Bezier Curve”.

Attachments:
noSweep.jpg (95.8 KB)


pezetko: Member; 387 posts; Joined: Nov. 2008; Offline

April 8, 2014 10:40 a.m.

Change curve primitive type from primitive to polygon and on the Sweep sop turn on Skin Output.


anon_user_21411066: Member; 210 posts; Joined: Jan. 2014; Offline

April 8, 2014 11:49 a.m.

pezetko
Change curve primitive type from primitive to polygon and on the Sweep sop turn on Skin Output.

Convert SOP doesn't offer this functionality….or what do you mean?


SreckoM: Member; 379 posts; Joined: Dec. 2006; Online

April 8, 2014 12:08 p.m.

You need just this http://screencast.com/t/a2MRR02wNNdX [screencast.com]
Circle node http://screencast.com/t/dpcjsYEmO [screencast.com]
Sphere node http://screencast.com/t/M7CghAagI [screencast.com]
Sweep node http://screencast.com/t/JMpSTyVLmR [screencast.com]


anon_user_21411066: Member; 210 posts; Joined: Jan. 2014; Offline

April 8, 2014 6:18 p.m.

Ah, ok now this works but the mesh it gives me is somewhat odd. On some edges it looks like it's swept along an edge twice, back and forth slighly offsetted.


SreckoM: Member; 379 posts; Joined: Dec. 2006; Online

April 9, 2014 5:38 a.m.

Screenshot or file please.


anon_user_21411066: Member; 210 posts; Joined: Jan. 2014; Offline

April 9, 2014 10:40 a.m.

This is a polysphere and for the sweep I used a circle as cross sesction. It's hard to see on a still image but it looks like for every edge the cross section got extruded twice slighly offsetted.
…and when I use a custom curve for the cross section the mesh looks totaly messy. It gets a bit better when I transform it a bit but it still is far away from production quality.

Attachments:
oddSweep.jpg (163.8 KB)
messyCustomCurve.jpg (121.6 KB)


eetu: Member; 606 posts; Joined: May 2007; Offline

April 9, 2014 10:49 a.m.

Helloes,

I took my above example, substituted the torus with a sphere and the cross section with a ‘plus’, and I am not seeing any double extrusions.

Attachments:
ee_edgecurves03.hip (76.6 KB)
ee_edgecurves03.jpg (156.8 KB)


eetu: Member; 606 posts; Joined: May 2007; Offline

April 9, 2014 10:52 a.m.

The vertices of the wireframe are another matter, creating beautifully joined junctions between a variable number of custom cross sections is a hard problem.


anon_user_21411066: Member; 210 posts; Joined: Jan. 2014; Offline

April 9, 2014 12:14 p.m.

Ah, I see. You use a wireframe and two converts before the sweep. Yes, that looks better although that's one again something I would have never thought of.
Thanks


eetu: Member; 606 posts; Joined: May 2007; Offline

April 9, 2014 12:23 p.m.

If one straight segment per edge is enough you can remove the second convert, it just changes the polylines to actual nurbs curves.


old_school: Staff; 2540 posts; Joined: July 2005; Offline

April 9, 2014 12:39 p.m.

Korny Klown2
Yes, that looks better although that's one again something I would have never thought of.

The most important tool to learning Houdini is the scene file as an example. If you haven't trolled through many of the help card example files, you should. The example files are sort of aligned to specific operators. After trolling through the example files, you get a real good idea as to what SOPs work with other SOPs.

The great many scene files out there are a tremendous resource to tap in to. Especially if they are commented like the example files that ship with Houdini.

You slagged the 20+ years of history earlier on. But on the other hand, there's 20+ years of clever users pounding on SOPs to learn. Get busy!

I love it when I see a whacky new set-up. Best part is that any artist can come up with the screwiest cool ideas.

There's at least one school like the old school!


grayOlorin: Member; 1799 posts; Joined: Oct. 2010; Offline

June 2, 2014 11:27 p.m.

I have also sometimes used a carve SOP to get primitive curves out of a wireframe although I cannot recall if I have tried it with an edge group… maybe you can use an edge group and a group transfer to highlight the curves from a carve sop which you want to keep and blast the other ones..? (sorry I cannot provide and example now

especially after's Jeff's comment..!)

i'll have to try it myself too at some point..!

cool to see the convert trick..!

-G

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