Closing Meshes in Open3D: Filling Holes and Boundary Detection

open3d, how to force the mesh to be closed. AttributeError: 'open3d.cpu.pybind.geometry.TriangleMesh' object has no attribute 'fill_holes' AttributeError: 'open3d.cpu.pybind.geometry.TriangleMesh' object has no attribute 'is_edge_boundary'

In Open3D, ensuring that a mesh is closed (i.e., it has no holes) can be a bit tricky since the library does not provide a direct method like fill_holes or is_edge_boundary for TriangleMesh. However, you can use a combination of methods to achieve this.

Here is a step-by-step approach to force a mesh to be closed:

1. Detect Boundary Edges: Identify the boundary edges of the mesh.
2. Fill Holes: Use the boundary edges to fill the holes.

Below is an example of how you can achieve this using Open3D and some custom logic:

import open3d as o3d
import numpy as np

def find_boundary_edges(mesh):
    edges = {}
    for triangle in mesh.triangles:
        for i in range(3):
            edge = tuple(sorted((triangle[i], triangle[(i + 1) % 3])))
            if edge in edges:
                edges[edge] += 1
            else:
                edges[edge] = 1
    boundary_edges = [edge for edge, count in edges.items() if count == 1]
    return boundary_edges

def fill_holes(mesh):
    boundary_edges = find_boundary_edges(mesh)
    if not boundary_edges:
        return mesh

    boundary_vertices = set()
    for edge in boundary_edges:
        boundary_vertices.update(edge)

    boundary_vertices = list(boundary_vertices)
    boundary_vertex_indices = {v: i for i, v in enumerate(boundary_vertices)}

    new_triangles = []
    for edge in boundary_edges:
        v0, v1 = edge
        for v2 in boundary_vertices:
            if v2 != v0 and v2 != v1:
                new_triangles.append([v0, v1, v2])

    new_triangles = np.array(new_triangles)
    new_mesh = o3d.geometry.TriangleMesh()
    new_mesh.vertices = mesh.vertices
    new_mesh.triangles = o3d.utility.Vector3iVector(np.vstack((np.asarray(mesh.triangles), new_triangles)))

    return new_mesh

# Load your mesh
mesh = o3d.io.read_triangle_mesh("path_to_your_mesh.ply")

# Fill holes
closed_mesh = fill_holes(mesh)

# Save or visualize the closed mesh
o3d.io.write_triangle_mesh("closed_mesh.ply", closed_mesh)
o3d.visualization.draw_geometries([closed_mesh])

Explanation:

1. find_boundary_edges: This function identifies the boundary edges of the mesh. An edge is considered a boundary edge if it is shared by only one triangle.
2. fill_holes: This function uses the boundary edges to create new triangles that fill the holes. It creates new triangles by connecting boundary edges with other boundary vertices.

Note:

• This is a simple approach and may not work perfectly for all meshes, especially complex ones with multiple holes or intricate geometry.
• For more advanced hole-filling techniques, you might need to use more sophisticated algorithms or libraries specialized in mesh processing, such as CGAL or MeshLab.

This should help you get started with closing meshes in Open3D.