How to find the intersection of two coplanar meshes

[Asli09]

I want to determine whether two coplanar meshes intersect, and if so, I want the intersection contours and want to cutMesh based on that intersection coutours. I've tried it, and it seems that the current method of intersection is not suitable for two coplanar meshes, if they overlap.

[Grantim]

Hello!

Could you please attach file samples or some images of what you have and what want to achieve?
It looks like you need something that is done inside MR::boolean function, have you tried it?

[Asli09]

I'm sorry, I didn't get what you meant. I want to get information about the intersection lines of meshC and mesh E to cut meshC. I have checked the parameters of MR::cutMesh, and the parameter MR::OneMeshContours is required, but I don't see the information of intersection line in the code you provided. Perhaps can you provide more complete code for me to understand? Your help will be greatly appreciated.

[Asli09]

I don't understand the need to triangulate contour after getting the contour of mesh C on a 2D plane. I don't see the code for mesh C and mesh E to find the intersection line. I just want to get the intersection information to cut mesh.

[Grantim]

Sorry for the delay.
Actually all intersection functions other functions related to boolean are designed for 3d: searching of plane edge intersections. So in fully planar case they will not good (though we resolve most degenerate cases in boolean, it does not seem like the result you want to achieve).

If you want exactly cutMesh call you will need to move from 2d intersections to 3d, for example:
lets say you want to cut red mesh intersection line on blue mesh

you can extrude red mesh - to make it 3d:

After this manipulation you will be able to operate cutMesh boolean and other related functions:

Will it work for you?

[Asli09]

I don't actually need the two points in the last blue triangle, because these two points are the intersection points of the extrude faces of the red triangle and the blue triangle. Perhaps can I project a triangle onto another triangle and then cut mesh after obtaining the projected outline？ Is there such a way？Which function do I need to call?

[Grantim]

If you only need to keep original outline - then simplest way is to convert both meshes into 2d contours and perform boolean operations in 2d as described in this comment. And if you need to get mesh back just triangulate resulted outlines.

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Perhaps can I project a triangle onto another triangle and then cut mesh after obtaining the projected outline？ Is there such a way？Which function do I need to call?

It will require much more complex code to prepare OneMeshContours like this, so if this two points are not fatal for your pipeline I suggest it is the most robust and simple way.