deleting prims with centroid within bounday

Forums Houdini Indie and Apprentice deleting prims with centroid within bounday

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deadalvs: Member; 196 posts; Joined: Aug. 2011; Offline

May 21, 2017 12:49 p.m.

hi,

how is it possible to check if prim's centroid is within an other specific volume (mesh)?

I know I can use the group so to test if points are within a volume and delete those points, but how would I do this for a primitive?

any input welcome!

thanks,
m.


matthias_k: Member; 483 posts; Joined: Dec. 2006; Offline

May 21, 2017 4:40 p.m.

something like this?

Attachments:
in_boundary.hip (77.3 KB)

English is not my native language, sorry in advance for any misunderstanding :-)


deadalvs: Member; 196 posts; Joined: Aug. 2011; Offline

May 22, 2017 9:48 a.m.

perfect - spot-on!

thanks so much!
matt


Konstantin Magnus: Member; 670 posts; Joined: Sept. 2013; Offline

May 22, 2017 7:28 p.m.

Here is a VEX solution that evaluates the normal directions of your mesh volume against the direction of the primitive centroids towards the closest points of the mesh volume.

Attachments:
prim_centroids_in_mesh.hipnc (259.8 KB)

https://procegen.konstantinmagnus.de/ [procegen.konstantinmagnus.de]


deadalvs: Member; 196 posts; Joined: Aug. 2011; Offline

May 26, 2017 5:29 p.m.

Hi,

thanks for the additional input - that's a cool alternative!


deadalvs: Member; 196 posts; Joined: Aug. 2011; Offline

May 27, 2017 1:32 p.m.

hi .. re the solution by matthias_k.

I actually can't use this approach, as the ‘centroid points’ for concave polygons can actually be outside the polygon and therefore within the volume I test against, which causes errors. But thanks for the input!


Konstantin Magnus: Member; 670 posts; Joined: Sept. 2013; Offline

May 27, 2017 5:50 p.m.

where is your ‘centroid’ then in a case like this?

Attachments:
centroid_q1.jpg (12.1 KB)

https://procegen.konstantinmagnus.de/ [procegen.konstantinmagnus.de]


matthias_k: Member; 483 posts; Joined: Dec. 2006; Offline

May 27, 2017 5:53 p.m.

:-)
many thanks for the response

English is not my native language, sorry in advance for any misunderstanding :-)


matthias_k: Member; 483 posts; Joined: Dec. 2006; Offline

May 27, 2017 6:02 p.m.

Hmmmm,
the question from Konstantin is perfect.
Maybe you need to convert every prim via primitive SOP to zero
and then check if the zero scaled prim points are inside your
“check against” geo.
But this can be slow, if I'm right

English is not my native language, sorry in advance for any misunderstanding :-)

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