I'm new to Blender. I am trying to find the intersection line between this mesh and another mesh, or a plane. I basically will have a plane at a certain height and I want it to cut through the cylinder-like-shape to get an outline where they touch that I can calculate an area, perimeter, etc., from.

I've tried with the intersect tools and the boolean modifiers, but I'm not having any luck getting it to do what I want. It will cut off the cylinder at a the plane, but I can't figure out how to extract the inner line that is highlighted in orange in the last picture.

Is there a simple way to do this? TIA

Top View

Side View

Boolean Modifier view


1 Answer 1


If you join the two objects (Object > Join), the following steps should get you the shape you need.

  1. Switch to Edit Mode.
  2. Deselect everything, then hover your mouse over the deformed cylinder, and press L to select it.
  3. Run Face > Intersect (Knife). This uses the selected geometry as a knife to cut the unselected geometry.
  4. In the Adjust Last Operation panel, set Separate Mode to Merge. This will clean the resulting geometry a bit, so I prefer and suggest to use it.


  1. The operator selects the resulting geometry, so we just need to delete everything else. Run Select > Invert then Mesh > Delete > Vertices.

The image below shows my test case.


  1. If you only want the outer edge of the intersection, you can delete the face (Mesh > Delete > Only Faces).

This procedure is destructive. If you want to keep the original objects, make sure to duplicate them first.

  • $\begingroup$ If I wanted to make a polyline with the vertices, how would I go about that? I would like to export the line into a format that I can use in CAD, ideally. $\endgroup$
    – CStarkey
    Dec 20, 2023 at 17:01
  • $\begingroup$ I am not sure which format will work. I suggest to look into the formats your CAD software can import and compare them with what Blender can export. Anyway, once you delete the faces, you can convert the mesh object to a curve object with Object > Convert > Curve. $\endgroup$
    – Mr A
    Dec 20, 2023 at 17:34
  • $\begingroup$ Excellent. Converting to a curve was what I was looking for!! Sorry, I didn't specify. I'm using Civil3D, but I don't think any of the files are friendly. I can use another software I have to convert though. Thanks for your help! $\endgroup$
    – CStarkey
    Dec 20, 2023 at 17:43
  • $\begingroup$ You're welcome! $\endgroup$
    – Mr A
    Dec 20, 2023 at 18:35

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