Detecting local self intersections mesh offset

Grasshopper
1

Hi everyone,

I am currently developing a Rhino / Grasshopper workflow (later integrated into a C# Rhino plugin) where I offset a mesh by moving vertices individually along their vertex normals.

The important part is: each vertex has an individual offset value → the values come from vertex colors,therefore I cannot simply use a standard global mesh offset or ShrinkWrap-only workflow

In generall it works really well, however for certain geometries (especially taller meshes with concave regions), I get local self intersections (e.g. picture. The white mesh is the original one; the red one is the offset mesh)

Screenshot 2026-05-18 133726
Screenshot 2026-05-18 1337261533×809 181 KB

These problematic areas later cause unstable mesh booleans. The issue is NOT global. It only happens locally in small problematic regions.

I am specifically looking for a robust way to detect these local self intersections BEFORE offsetting the mesh.

Things I already tested:

  • Mesh repair approaches

  • MeshRay / MeshLine collision tests

  • Comparing old/new edge lengths

  • Testing offset rays against original mesh

I am now wondering:

  1. Is there a known robust strategy for detecting local self intersections?

  2. Has anyone implemented something similar in Grasshopper / RhinoCommon?

The solution ideally needs to work either in Grasshopper or RhinoCommon.

Any ideas, plugins, RhinoCommon methods, or computational geometry approaches would be hugely appreciated.

Thanks!

2

What is the topology of your meshes?

Looks like grid type in the screenshot.

You could create polylines by vertices in U and V on the original mesh-grid, offset these, and test for self intersection.

3

Hello,

1.Is there a known robust strategy for detecting local self intersections?

https://developer.rhino3d.com/api/rhinocommon/rhino.geometry.mesh/getselfintersections