import numpy as np
import open3d as o3d
import os
import sys

# monkey patches visualization and provides helpers to load geometries
sys.path.append('..')
import open3d_tutorial as o3dtut
# change to True if you want to interact with the visualization windows
o3dtut.interactive = not "CI" in os.environ

Half Edge Mesh

This tutorial outlines the following:

1. How to use mesh_show_back_face to render the backface of a mesh.
2. How to use geometry.AxisAlignedBoundingBox to crop a mesh.
3. How to use utility.Vector3dVector to colorize boundary vertices of a mesh to red.

Render the backface of a Mesh

In order to render the backface of a mesh visualization.draw_geometries() is called with the flag mesh_show_back_face set to True.

# Initialize a HalfEdgeTriangleMesh from TriangleMesh
mesh = o3d.geometry.TriangleMesh.create_sphere()
bbox = o3d.geometry.AxisAlignedBoundingBox()
bbox.min_bound = [-1, -1, -1]
bbox.max_bound = [1, 0.6, 1]
mesh = mesh.crop(bbox)
het_mesh = o3d.geometry.HalfEdgeTriangleMesh.create_from_triangle_mesh(mesh)
o3d.visualization.draw_geometries([het_mesh], mesh_show_back_face=True)

Cropping a Mesh

geometry.AxisAlignedBoundingBox is used to create an axis aligned box. The parameters min_bound and max_bound take an array of cartesian coordinates (x,y,z) and define the size of the bounding box. The bounds are set such that the y-axis of the sphere mesh is cut by a call to crop.

# Colorize boundary vertices to red
vertex_colors = 0.75 * np.ones((len(het_mesh.vertices), 3))
for boundary in het_mesh.get_boundaries():
    for vertex_id in boundary:
        vertex_colors[vertex_id] = [1, 0, 0]
het_mesh.vertex_colors = o3d.utility.Vector3dVector(vertex_colors)
o3d.visualization.draw_geometries([het_mesh], mesh_show_back_face=True)

Colorize the Boundaries of a Mesh

A call to geometry.TriangleMesh.get_boundaries returns a vector of boundaries, where each boundary is a vector of vertices. Each vertex color is represented by an RBG array and Vector3dVector is used to convert vertex_colors of shape (n, 3) to Open3D format. Finally, the vertex colors are set on the mesh.