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deadpixel

Select Outside Edges Only

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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Create a polyfill to close the holes for the time being, put them in a patch group under "Output Groups", and remove the primitives in "patch" group when you are done?

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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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Yeah totally appreciate it is not reallly a 'hole' :)

my thoughts are something along the lines of vertex/nearest-point count to isolate the diagonal on the enclosure...will have to try when back at houdini

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I'm leaning towards exploiting VDB (or anything volume based)...coz those 2 pts would be 'enclosed'...but am not competent enough with VDB I'm afraid...

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2 hours ago, Noobini said:

YES...done it !!! I will not be defeated...

 

ha, nice idea !

 

Ill test when I get back home to see how it holds up to a few ideas I have

thanks Noobini! :)

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