Extract faces from a Brep

[Pascal]

Hi all- I am messing with a script that involves removing faces from a brep. At the moment, the way I am doing this works but seems a little clunky- there must be a better way: I identify all the faces in the original brep that I want to extract and and duplicate them, and add them to the document. Then I duplicate all the other (non-extracted) faces in the original and join into a new brep, add that to the document, and then delete the original brep.
This works in most cases, even if it is not the most efficient, but where it falls down is when some faces are bad-- so far, bad faces are not duplicated and that throws the rest of the script off.

Any ideas?

thanks, Pascal

[nart]

I don't know how to select faces of a brep, but if you can figure out their index in the Rhino.Brep.Faces list then you can use:

Rhino.Geometry.Collection.BrepFaceList.RemoveAt()

This seems to work here:

import rhinoscriptsyntax as rs
import scriptcontext as sc
import Rhino


brep = rs.GetObject('pick brep')

rBrep = rs.coercerhinoobject(brep)

#to check face list
for face in rBrep.Geometry.Faces:
    print face
    

#remove a face from the face list
rBrep.Geometry.Faces.RemoveAt(1)

#make a new brep by duplicating the original but now has 1 face deleted
newRBrep = rBrep.DuplicateBrepGeometry()

print 'CHANGE'#just to break lists

#to check face list of new brep...should be -1
for face in newRBrep.Faces:
    print face
    
#this replaces the original brep in the document with the new on without the face
sc.doc.Objects.Replace(brep, newRBrep)

#redraw views
rs.Redraw()

[Pascal]

Hi, thanks a lot- that is what I was looking for. And yet I am not sure I can use it in this script because, as far as I can see, only one face at a time can be removed- I have a list of indices and I want to remove them all but of course each one I remove rearranges the indices in the brep so that after the first one, the wrong faces are removed. Sigh.

Also, now I see there is an ExtractFace method, which may help simplify things as well.

thanks again,

-Pascal

[Steve Baer]

I typically remove things from a list in reverse order (face8, face5, face4,...) since this way the indices stay the same for what you want to remove.

[Pascal]

Hi Steve- OK! thanks--- so simple... works fine.
-Pascal

[Pascal]

Hi Steve - One more thing- the result can be a disjoint brep; are there any tools for detecting these and splitting them up? I'm not seeing anything so far. Thanks.

-Pascal

[nart]

I typically remove things from a list in reverse order (face8, face5, face4,...) since this way the indices stay the same for what you want to remove.

Steve - Is there an easy way to find the parent brep of a surface?

Thanks,

Nathan