# Geometry Nodes Fields - Semi Circle

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.

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

So it is not useful information to sort vertices.

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

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

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

• Why clamp X to -1000? The result seems like it's clamped to 0 🤔 Commented May 6, 2022 at 8:41
• It is for saving X value as it is, Y will be from 0 to radius Commented May 6, 2022 at 8:42
• 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?) Commented May 6, 2022 at 8:45
• Any particular reason for not just using arc curve primitive?
– Ratt
Commented May 6, 2022 at 8:52
• Well, nice suggestion=-) Commented May 6, 2022 at 8:54

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:

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

• Thanks! I'm going to try implement the arc approach into my set up but I can see the curve approach being useful too. Commented May 6, 2022 at 9:14

I would prefer to use the node Arc (Blender 3.1+)

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:

• Seems like a niche solution that someone might need for an obscure project in 5 years time. Commented May 6, 2022 at 9:17