[Sidefx-houdini-list] Grouping Outside Faces

François Duchesneau sidefx at trinix.ca
Wed Jan 2 21:05:10 EST 2008


Ok, here's how to do it. Forget the first method because I thought the 
PolyExtrude would promote the points inside a group to the corresponding 
extruded points. Anyway it's better the following way.

For this, I assume your inner faces are all in pair of two because you 
want to have many cubes from the extruded grid.

1-Create an other PolyExtude Sop but check "Remove Shared Sides" on this 
one.
2-Append an AttribCreate after the second PolyExtrude and create a 
primitive attribute, let's say "inner" and set the value to 1.
3-Append an AttribTransfer after the first PolyExtrude and set the 
"Distance Threshold" to 0.001 for example.
4-Create a Group Sop with "Group by Expression" set to $INNER==0

... and you're done. You can also look at an example file I've posted on 
the Exchange called "Transparent Shattered Glass" that uses an other 
mechanism that put every coincident faces into a group without having to 
duplicate the PolyExtrude.

François

François Duchesneau wrote:
> I'm sorry. I answered too quickly without cross-checking what I was saiying.
>
> I think you'll have to do an intersection boolean operation with the 
> "extrudeSide" group from the PolyExtrude.
>
> I test that and let you know.
>
> François
>
> François Duchesneau wrote:
>   
>> You can append a Group Sop before the extrude, set the type to "Point" 
>> and go in the "edge" tab and check "Unshared Edges". This creates a 
>> group of all points being the boundary. Invert the group with a boolean 
>> operation inside that Group Sop to get all points that are not a boundary.
>>
>> All the edges in that group will be included inside the geometry after 
>> the extrude.
>>
>> François
>>
>>
>> Edmond Earl Smith wrote:
>>   
>>     
>>> Hello everyone, I have a fractured object that I create by extruding a 
>>> grid and partitioning the pieces.  I would like to group just the faces 
>>> that are "inside" the object.  Much like the group extrudeSide when you 
>>> use the polyextrude but without the outer faces, just the inner ones.
>>>
>>> thanks,
>>> Eddie
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