[Sidefx-houdini-list] Grouping Outside Faces

François Duchesneau sidefx at trinix.ca
Thu Jan 3 17:46:02 EST 2008


Do you use the Dop Import Sop? It keeps the grouping of the incoming 
geometry.

Maybe you can also use CHOP to have more control. Look at the example 
called "ExtractTransforms" in the "Dynamics Chop" example file. However 
I'm not sure it will work as is since it transforms at the obj level.

François

Edmond Earl Smith wrote:
> Hey thanks for the help.  I got something to work that's a little like 
> your suggestions.  I just had to do some fancy grouping.  One of the 
> bigger challenges is going to be getting this information to transfer 
> through DOPS and back into SOPS.  DOPS reassigns the RBD glued objects 
> so that each group is a separate RBD object.  When it does this it 
> reassigns the faces per object, so it's not like I can even create a 
> group and try and reference the faces later once they've been 
> simulated.  I have no clue how to grab these inner faces once the DOP 
> sim has gone through.  Any suggestions? 
>
> Thanks again so much,
> Eddie
>
> François Duchesneau wrote:
>
>
>   
>> 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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>>>>>   
>>>>>     
>>>>>       
>>>>>           
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