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enter image description hereI have a collection of hexes in a sphere shape. I want to be able to affect only the top when I extrude. However, since I'm not capturing the top face correctly, it's extruding all faces in the collection.

How can I capture only the outer most face (white polygons) of the objects in my collection with geometry nodes to be able to extrude? I apologize for the picture. Couldn’t post from my machine for some reason.

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  • $\begingroup$ I guess one idea would be to select by material index and then add my extrude node. Working out how to set that part up. $\endgroup$ Commented Sep 19, 2022 at 16:33

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The most obvious solution is to save the information about the top as an attribute, and then use it:

But what if you don't have that information?

Good job on recovering and figuring out you actually did save that information, as a material slot index. If you didn't, you could still try to recover, for example by comparing the normal of a face with the direction towards/away from the center:

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  • $\begingroup$ Thank you! This was very helpful! @Markus von Broady $\endgroup$ Commented Sep 19, 2022 at 22:47
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For those that are noobs like myself, here is a solution I figured out that works pretty well for what I’m trying to do. I can't upload screenshots from this pc, so I'll do my best to describe the simple node setup.

--Collection Info connected to Extrude mesh --Use a noise Texture node to offset the Extrude Mesh scale. --Used a material index connected to an Equal node for selection of face by its material index value. --Connected Extrude Mesh to Geometry input and Equal node to Selection input on set material node just to see if the effect is working using some random color.

Hope this is helpful for someone :) enter image description here

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    $\begingroup$ Hello, thanks for the answer but the quality is really poor, could you add a screenshot directly from your computer or describe with words how you solved it ? $\endgroup$ Commented Sep 20, 2022 at 6:55
  • $\begingroup$ @Gorgious I apologize, I can't upload screenshots from this pc. I added a description to what I did for this set up. I hope that helps. $\endgroup$ Commented Sep 22, 2022 at 14:50
  • $\begingroup$ Thank You for writing it in text. :) $\endgroup$ Commented Sep 22, 2022 at 15:08

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