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Select Outside Edges Only


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Hi

I can successfully group unshared edges to get the boundary edges of a flat grid.  

However, how might I procedurally remove the very inside enclosed hole edges (such as the three holes in the attached image), and only have the very outside perimeter remain in the group?

Any advice appreciated

boundaryEdges.png

Edited by deadpixel
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extremely easy............once you know how that is....
(in your case...you may have to select more than 1 groups because of 2 islands....so probably border__0 and border__1)

Just in case youtoobe plays up and you can't watch...the gist of it is:

01) in your group select unshared edges...make sure you tick Create Boundary Groups, then if you have a 'normal' boundary plus 2 inside holes...=> you'd have 3 Boundary Groups

02) in your next group select, in the dropdown list you'd see border__0, border__1, border__2, ....border__0 should be the outside one...the other 2 would be the holes..you can go nuts with all sorts of permutation/combinations with your group selections...

Now you know how easy it is....just say OMG !!!

Edited by Noobini
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Ah it is so absurdly easy, thank you guys!!

My problem stemmed from a situation where I couldn't actually select Create Boundary Groups as it was greyed out in the group node...so I overlooked it.... but it turns out this was because I had set to group 'edges' and not to 'points'

Thanks again, these are all great options, and I really appreciate the time taken!

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Interestingly the third enclosed hole does provide a bit of a conundrum...

...polyfill doesn't recognise it as a hole, and the boundary groups isolate the two main outer islands, but seemingly no shared points.

My need would be to make sure all 'inside/enclosed' edges are removed from the very outside perimeter group.

Ive just tried messing about with group combine to see if there are some logical combinations of the point group that could isolate it, but not much luck so far

A few ideas I'm intending to test when I'm back at my computer would be to promote the group to edges/prims and try a combination of shared points to try to isolate it, or possibly by vertex count of the points....any thoughts?

boundaryHoles.png

Edited by deadpixel
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just did quick a test to see what would happen if the inside boundary length is LONGER than the outside one...from the result...I would say it's safe to simply pick the first one (if you want the outside, with no other islands) ie....xxx__0 group.

 

Outside.jpg

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6 minutes ago, deadpixel said:

Interestingly the third enclosed hole does provide a bit of a conundrum...

...polyfill doesn't recognise it as a hole, and the boundary groups isolate the two main outer islands, but seemingly no shared points.

My need would be to make sure all 'inside/enclosed' edges are removed from the very outside perimeter group.

Ive just tried messing about with group combine to see if there are some logical combinations of the point group that could isolate it, but not much luck so far

A few ideas I'm intending to test when I'm back at my computer would be to promote the group to edges/prims and try a combination of shared points to try to isolate it, or possibly by vertex count of the points....any thoughts?

boundaryHoles.png

so in this case doesn't select groups xxx__0 and xxx__1 do the job ?

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14 minutes ago, Noobini said:

so in this case doesn't select groups xxx__0 and xxx__1 do the job ?

No, as it also includes two points inside 3 that are not part of the very outer perimeter (if you consider the two main islands to be connected and 3 to be a hole inside)

 

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mmm....I could argue that is is correct coz there's TWO outside boundaries...each and every one of those 4 pts in 'hole' 3 (and I agree with polyfill here that 3 is NOT a hole) is on the very outer perimeter...but yeah for what you want to deselect the 2 diagonal ones...it's tricky....procedurally...

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  • 1 year later...
  • 1 year later...

usually grouppromote, then you may need to experiment with Include Only Elements on the Boundary or Include Only Elements Contained in Orig Group.

but in simple cases where there are no holes, why don't you just select unshared edges in the first place ?

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Hey guys

To fix some Voronoid cluster issue, im trying to heal some edge hole problem in the middle on my assembly. I was thinking to go from world space to a planar UV space to extract the boundary of my mesh but the polyexpand2d fail to works and

On 27/06/2017 at 12:14 AM, animatrix said:

There are many ways to do this but one way I would do is delete all groups but the largest one by element count using something like this:

https://www.dropbox.com/s/lkl7j2w6r65r2im/DeleteGroupsByCount_SOP_Animatrix.otl?dl=1

Is that expansive to do a loop check for all possible prim group and keep the latest one?

 

In planar, i think i could isolate the disconnected pieces, do a bound with a rectangle, resample it than do a ray sop to wrap and get the outside border. I guess it should work

 

Overall, if i tried different approaches from building these procedural patterns, in this setup im using something similar to Matt Estala Voronoid setup for H17 as a base

https://www.tokeru.com/cgwiki/?title=Houdini

As soon as the number of scatter points increase, It creates all these disconnected problems shown here which i didn't expect for such a basic setup... I wish i could also have scales xyw attributes to have a slighty better control for the cluster shape like in the old h16 voronoid

 

image.thumb.png.4c4d9fc4541070b2f20698ebb5d8e8af.png

Did i miss something?

How you usually deal with that on a custom input form. using Voronoi

(Here i tried to avoid, VEX define pattern, Cops, Pop)

 

Thanks guys, take care

 

________________________________________________________________

Vincent Thomas   (VFX and Art since 1998)
Senior Env and Lighting  artist & Houdini generalist & Creative Concepts  (Available)

https://www.imdb.com/name/nm0859628/
 http://fr.linkedin.com/in/vincentthomas

 

image.png.3b90be684a43bda4194ebc5064b55364.png

 

sci_fi_hull_generator.gif

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I tried a different approach on our couple Pig & Squid, i could  get large polish hard surface plate but still like to find out :mellow: , hmm.

________________________________________________________________________________________________________

Vincent Thomas   (VFX and Art since 1998)
Senior Env and Lighting  artist & Houdini generalist & Creative Concepts  (Open for new opportunity)

http://fr.linkedin.com/in/vincentthomas
 http://fr.linkedin.com/in/vincentthomas

 

 

image.png.9b9f99c4fb2073642314a1ee5c293dad.png

image.thumb.png.5795f844922c387b5b2cfe7677b7b1a8.png

image.thumb.png.c79dd0ddd78a640485cac34fa427774f.png

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