How can I add polygon faces to a group, without displaying this group… as displaying it hides the polygon faces I want to select.. ?
I did a small video to explain the situation. Please check it.

What I tried to do: Create a second group, select the inside faces, then copy paste the selected components list from the second group to the first group , then delete the second group : it does not work.

What's the solution for this? Visibility nodes?

Thanks
Gz

You could hide the first selection, true, but then you need to make a temporary group for the second selection and merge with the first (group combine). Delete or blast changes the prim order so don't do that. Either name the first group “_3d_hidden_primitives” or use a visibility node to hide it without changing the topology.

Personally, I would get my camera in there and look from the other side and avoid messing with operations that interrupt the flow.

Also, I see you are importing an alembic. Before spending time manually selecting faces, I would check if the selection I'm about to make already exists as a shape node(s) in the alembic hierarchy.

Hello Jsmack, thanks for the help.

First about the camera inside, yes that's what I do but sometimes it's not possible. This shoe scene is just an example. Imagine there was a sock inside the shoe and the shoe and sock would be the same single mesh. That's what I'm confronted with these days as I'm working with imported single mesh CAD objects that have many faces sticked on top of the other. And unfortunately there is no useful primitive islands (or clusters) in the imported Alembics or STL.

You taught me something new: I didn't know you could hide a group by naming it “_3d_hidden_primitives”. Where in the doc could I read more about this? Something I noticed with this name is that it doesn't work right away. I had to press the Bypass button on the node, then uncheck it, to have the primitive faces disappear.

So following your advices, I set up a network to be able to select inward primitive faces, then delete all faces I wished. Here is a pic showing what I did. Please tell if this is what you had in mind. Thanks!!

Gz

Hi, not sure if it's suitable but two options I've found useful for imported geometry are;

1. Viewport group selection - In selection mode (S), above viewport, click groups or press 9, use drop down for selection options. “3d Connected Geometry” or “Alembic Paths” might be good options.
2. Assemble SOP - Similar to “3d Connected Geometry” above and I find it's a quick way to create multiple groups from geometry.

Rob

Hello Rob, many thanks for the useful tips. These will come in handy next time I have to select merged multi parts objects.
However, I'd like to know how to handle the specific case I'm showing on the video, when a selection group hides other primitive faces I want to add to the selection. is the setup in my picture correct?
Thanks,
Gz

Perhaps set group by bounding box/object (adjust as you go) and put this into visibility node.

Once your first faces are in your group and hidden, how about selecting your additional faces and setting their group_groupname integer attribute to 1? Won't that add them to the existing group in one step?

Hey Tanto. Here's what I did :
- Select outisde primitive faces, create a group and name it “_3d_hidden_primitives”. The faces get hidden.
- Select inside primitive faces, go to Geometry Spreadsheet, display primitives, view > only show selected. Then I can see a column reading “_3d_hidden_primitives” with all values at 0. I tried to change these values to 1, but it does not accept it: the values remain at 0.

Hello Babaj, I found the bounding box option in the group parameters pane, but I don't know what to do with it. Could you give me more info? Thanks.

Gz

Jsmack's solution is the way to go if you want to add inside selection to outside and I'd use the visibility sop as it's easier to toggle or move.
Name the outside group as “Toe_Bump”, use visibility to hide Toe_Bump, select and name the inside also to “Toe_Bump” using another group but change the Initial Merge from Replace Existing to Union with Existing. (you don't need the group combine sop)
ie. Group, Visibility, Group (union). Then you can bypass the Visibility or move it under both group sops and change the Apply To Non-selected Primitives.

If the inside is just an extrude of the outside… Separate the inside from outside, delete inside, work on model and extrude later.
To separate, you could look for the connecting polys. ie. if you think of the boot as a Houdini PolyExtrude, extrudeFront = Outside, extrudeBack = Inside, extrudeSide = connection between Inside and Outside. (so delete extrudeSide, use assemble, delete inside)

Rob

Hey Rob, thanks a lot for taking the time to help through this pic and scene file. MUCH apreciated!
I didn't know two groups could have the same name and I didn't pay attention to this “initial merge” menu.
Soo your experience is very helpful :0)

Just now I found another solution that is very simple. It is so simple that perhaps I overlooked it. Here is what I did:
- Select outside primitive faces.
- Create Group1 from this selection.
- Use a Visibility node to hide Group1.
- Select inside primitive faces.
- Create Group2 from this selection.
- In group 2, copy the list of primitives.
- In group 1, go to the end of the list of primitives, add a space, then paste.
- Delete the visibility node and Group2.

But all these solutions are a bit too long to do, even the simple ones. In other 3D apps it's quicker. I wish Sidefx could improve this workflow. Here is what I use to do in Softimage:
- Select outside primitive faces.
- Create a cluster from this selection. A cluster is a components group.
- Hide the selected faces using hotkey “H”.
- Select inside primitive faces.
- CTRL Select the cluster.
- Menu “add selection to cluster”