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Do you know how to transfer/combine vertex group attributes from collection instances to the final geometry nodes model? I need them as vertex informations for other modifiers or objects. In this case I need the vertex group center as a position attribute for an empty object.

Here's the Blend file:

Someone knows a solution?

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  • $\begingroup$ I think your problem comes down to the vertex group being converted to an attribute. You can convert it back to a vertex group using this trick: blender.stackexchange.com/a/275405/60486 $\endgroup$
    – Markus von Broady
    Commented Nov 30, 2022 at 18:23
  • $\begingroup$ Thank you. But this was not the solution or I've made something wrong. Added my scene to my question if someone like to test it. $\endgroup$
    – Christoph Werner
    Commented Dec 1, 2022 at 8:52

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This setup works for me. The Vertex Group "Group" is transferred to the output mesh as an attribute. However, it's not converted to Vertex Group information in the output mesh. It remains an attribute.

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I tried figuring this out but I think there are several problems here:

  1. You can not change an object's location from GN => you can't move the Empty (or any other object) from within GN
  2. To move the empty you will need a Copy Location constraint on it and that constraint would actually support a Vertex Group (VG)
  3. BUT you can't set/fill a VG from GN and if I understand this correctly, that will also never be possible (see https://blender.community/c/rightclickselect/79gG) They write that the old and slow VGs are not good for pushing data through the modifier stack and GN will therefore not support VG outputs but it seems they forgot to consider constraints which do use VGs? 🤔
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  • $\begingroup$ Hi ChrisP. Thank you for the infos. About point 1: You can move empties via geometry nodes. Set Position works and Transform also. You've to use the Object Info node for this and set the "As Instance" option, inside a geometry. But GNs can't be added to empties themself. $\endgroup$
    – Christoph Werner
    Commented Dec 1, 2022 at 15:41
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Christoph,

ad Empty As Instance: But you are not moving the actual empty this way. Correct? So you can't really do anything with it outside of the GN-tree.

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  • $\begingroup$ Exactly... useless. Unfortunately. :( $\endgroup$
    – Christoph Werner
    Commented Dec 2, 2022 at 12:45
  • $\begingroup$ The only way to move an empty to a vertex position of an extenal mesh is to use object info and add a group to the gn source mesh by using the same name like the one in the external model. Then the empty can be moved by a copy location constraint. But this don't work with collection content. $\endgroup$
    – Christoph Werner
    Commented Dec 2, 2022 at 12:54

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