How do I get a group boundary?

Forums Houdini Lounge How do I get a group boundary?

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EDITH: Member; 19 posts; Joined: Jan. 2020; Offline

Feb. 11, 2020 4:39 a.m.

Like in the picture, I'm trying to get a boundary between groups, but mine seems strange.
I followed the lecture as it was, but it got strangely guarded.
What should I do?

Edited by EDITH - Feb. 11, 2020 05:06:36

Attachments:
20200211_183543.png (30.4 KB)
20200211_183600.png (279.9 KB)
20200211_183729.png (13.5 KB)
1_uv_render.hip (981.6 KB)


Aizatulin: Member; 504 posts; Joined: July 2005; Offline

Feb. 11, 2020 3:55 p.m.

Hi,

here are some thoughts. There probably many approaches but one might be using an integer (point/primitive) attribute and loop over all points/prims and check all their neighbours. If one neighbour has a different value compared to the point/prim itself, the point/prim should be a border.

Attachments:
1_uv_render_group.hipnc (963.6 KB)


vusta: Member; 555 posts; Joined: Feb. 2017; Offline

Feb. 11, 2020 5:21 p.m.

not quite sure what you're after tbh,

here I used trace:

Attachments:
Groups.gif (963.0 KB)
vu_butterflyGroups.hiplc (138.0 KB)


EDITH: Member; 19 posts; Joined: Jan. 2020; Offline

Feb. 12, 2020 9:28 a.m.

Aizatulin
Hi,

here are some thoughts. There probably many approaches but one might be using an integer (point/primitive) attribute and loop over all points/prims and check all their neighbours. If one neighbour has a different value compared to the point/prim itself, the point/prim should be a border.

Thank you for your detailed information


EDITH: Member; 19 posts; Joined: Jan. 2020; Offline

Feb. 12, 2020 9:30 a.m.

vusta
not quite sure what you're after tbh,

here I used trace:

Thank you for making it easier for me to understand with your gif


Jonathan de Blok: Member; 294 posts; Joined: July 2013; Offline

Feb. 12, 2020 4:54 p.m.

In H18 there is an expand groups sop. If you give it a negative value it will shrink all groups. So after shrinking by -1 all prims that endup not being in a group are the boundary.

More code, less clicks.


tamte: Member; 9380 posts; Joined: July 2007; Offline

Feb. 12, 2020 5:46 p.m.

in H18 there is also Group from Attribute Boundary SOP as well as Group Promote SOP has option to extract the boundary from existing groups

Tomas Slancik
CG Supervisor
Framestore, NY

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