How to intersect two meshes to get a line? I can export?

Question

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

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.

5. 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.

6. 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.