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Is it possible to create a semi-circle with Geometry Nodes?

It's for a particle system, so a math based approach rather than a boolean approach would be ideal to keep the vert count/calculation time down.

I've used the below method for a semi-circle but cant seem to get it to work for a single face circle. My thinking was that if I rotated the normal 90° the same approach would work, but I'm probably miss-understanding how normals work.enter image description hereenter image description here

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4 Answers 4

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If you make a face, all normals will point up:

enter image description here

So it is not useful information to sort vertices.

If you want to keep one face, you can basically shift points from one side:

enter image description here

You can also go nuts and recreate the half of a circle, so that the straight line will consist of 2 points:

enter image description here

Super easy node setup from Ratt, with usage of curve Arc primitive and then converted to mesh:

enter image description here

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  • $\begingroup$ Why clamp X to -1000? The result seems like it's clamped to 0 🤔 $\endgroup$
    – Markus von Broady
    Commented May 6, 2022 at 8:41
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    $\begingroup$ It is for saving X value as it is, Y will be from 0 to radius $\endgroup$
    – Crantisz
    Commented May 6, 2022 at 8:42
  • $\begingroup$ Aaah thanks for clarifying, the axis are shown on the screenshot so I should have figured it by myself. It would be nice if nodes values supported infinities (or do they?) $\endgroup$
    – Markus von Broady
    Commented May 6, 2022 at 8:45
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    $\begingroup$ Any particular reason for not just using arc curve primitive? $\endgroup$
    – Ratt
    Commented May 6, 2022 at 8:52
  • $\begingroup$ Well, nice suggestion=-) $\endgroup$
    – Crantisz
    Commented May 6, 2022 at 8:54
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You can also do this using a curve circle, separating based on position instead of normal, then filling afterwards to make an N-Gon. Something like this:

Semi Circle Node Graph

Edit: As Ratt pointed out under Crantisz answer the arc primitive exists for this very purpose

Arc is Better

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  • $\begingroup$ Thanks! I'm going to try implement the arc approach into my set up but I can see the curve approach being useful too. $\endgroup$
    – special_frog
    Commented May 6, 2022 at 9:14
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I would prefer to use the node Arc (Blender 3.1+)

enter image description here

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This is by far the worst solution, but perhaps of some educational value (like what to avoid):

Left is triangle fill (notice overlapping face), right is n-gon fill:

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    $\begingroup$ Seems like a niche solution that someone might need for an obscure project in 5 years time. $\endgroup$
    – special_frog
    Commented May 6, 2022 at 9:17

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