cutMesh Function Not Producing Expected Results (Empty removed_mesh)

[Phbayo]

import numpy as np
from meshlib.mrmeshpy import Mesh, Vector3f, loadMesh, saveMesh, findProjection, convertMeshTriPointsToClosedContour, cutMesh, fillContourLeft


def cut_mesh(mesh: Mesh, loop_points: list[float], get_bigger_part: bool) -> tuple[Mesh, Mesh]:

    mesh_clone = Mesh()
    mesh_clone.addPart(mesh)

    tri_points = []
    for i in range(0, len(loop_points), 3):
        v3 = Vector3f(loop_points[i], loop_points[i + 1], loop_points[i + 2])
        projection = findProjection(v3, mesh_clone)
        tri_points.append(projection.mtp)

    contour = convertMeshTriPointsToClosedContour(mesh_clone, tri_points)

    contours = [contour]
    cut_result = cutMesh(mesh_clone, contours)

    edge_path = cut_result.resultCut[0]
    one_part = fillContourLeft(mesh_clone.topology, edge_path)
    other_part = mesh_clone.topology.getValidFaces() - one_part

    if get_bigger_part:
        kept_part = one_part if mesh_clone.area(one_part) > mesh_clone.area(other_part) else other_part
        removed_part = other_part if kept_part == one_part else one_part
    else:
        kept_part = one_part if mesh_clone.area(one_part) < mesh_clone.area(other_part) else other_part
        removed_part = other_part if kept_part == one_part else one_part

    kept_mesh = Mesh()
    kept_mesh.addPartByMask(mesh_clone, kept_part)
    kept_mesh.pack()

    removed_mesh = Mesh()
    removed_mesh.addPartByMask(mesh_clone, removed_part)
    removed_mesh.pack()

    # return kept_mesh, removed_mesh,cut_path_vertices
    return kept_mesh, removed_mesh


if __name__ == "__main__":

    ori_mesh = loadMesh("./teeth_output/teeth_stl/23527_lower_f.stl")

    loop_points = [18.932043075561523, 0.08174850046634674, 0.2867463529109955, ...]
    
    kept_mesh, removed_mesh = cut_mesh(ori_mesh, loop_points, get_bigger_part=True)
                               
    saveMesh(kept_mesh, "./teeth_output/process/23527_lower_kept.stl")     # save part
    saveMesh(removed_mesh, "./teeth_output/process/23527_lower_removed.stl")    # cut part

test_file.zip

Hello,
Issue: cutMesh Function Not Producing Expected Results (Empty removed_mesh)
Description
I am using the meshlib. mrmeshpy library to cut a dental mesh (. stl file) using a set of 3D points that define the cutting contour. My expectation is that the function cutMesh should return two separate meshes:

kept_mesh: The part that is retained after cutting.
removed_mesh: The portion that has been cut away.
However, removed_mesh is empty (contains no faces), which suggests that the cutting operation may not be performed correctly.May I ask if this is because of my stl file (mesh) problem or loop_points problem? How should I solve this problem to make correct cutting?I have uploaded an example of not cutting correctly, which contains a tooth mesh and corresponding loop_points that need to be cut.

[Grantim]

Hello!

Actually, your code is OK, but mesh has tunnel, that why fillContourLeft leaks out of cut path. fillContourLeftByGraphCut is more robust in such scenarios, it uses "minimum cut" algorithm to separate what's inside and what's outside of initial cut contour, effectively dividing tunnels.

Please give it a try, change your fillContourLeft on this:

    one_part = fillContourLeftByGraphCut(mesh_clone.topology, edge_path, edgeCurvMetric(mesh_clone))

edgeCurvMetric - is by default scores edges by their curvature preferring concave cuts, you can change arguments to find best convex cut, use other metrics, but it your case default arguments is what you need.

[Phbayo]

Thank you very much for your response! Your solution is very effective and successfully resolves the issue of cutting path leakage. However, I have noticed that the mesh boundary generated by this cutting method is not very smooth and appears jagged or uneven.

My original goal was to achieve a smooth cutting boundary directly during the cutting process, rather than relying on post-processing to smooth it afterward.

I would like to ask:
Is there a way to achieve a smoother cutting path during the cutMesh process itself, so that the resulting kept_mesh and removed_mesh naturally have smooth boundaries?

If so, how can this be implemented? Are there specific parameters or methods that need to be adjusted?

I appreciate your help! 😊

[Grantim]

So, I believe that cutMesh produces smooth boundary, but there are also other boundaries that are produced by tunnels separation.
You can try to use smoothRegionBoundary function before separation.

one_part = fillContourLeftByGraphCut(mesh_clone.topology, edge_path, edgeCurvMetric(mesh_clone))
smoothRegionBoundary( mesh_clone, one_part )

Hope it helps!