Face Markers and Surface Data

Demonstrate the usage of several attributes of tetgen.TetGen.

You can access faces and edges from an instance of tetgen.TetGen from the tetgen.TetGen.trifaces and tetgen.TetGen.edges attributes.

# sphinx_gallery_thumbnail_number = 1
import numpy as np
import pyvista as pv
import tetgen

First, let’s tetrahedralize a sphere.

sphere = pv.Icosphere(nsub=1)
tet = tetgen.TetGen(sphere)
tet.tetrahedralize(order=1, mindihedral=20, minratio=1.5, regionattrib=True)
tet.grid

UnstructuredGrid	Information
N Cells	80
N Points	43
X Bounds	-1.000e+00, 1.000e+00
Y Bounds	-1.000e+00, 1.000e+00
Z Bounds	-1.000e+00, 1.000e+00
N Arrays	0

Next, let’s construct a pyvista.PolyData from the triangular faces, accessible from the tetgen.TetGen.trifaces attribute.

# mesh containing both exterior and interior elements
trimesh = pv.PolyData.from_regular_faces(tet.node, tet.trifaces)
trimesh

PolyData	Information
N Cells	200
N Points	43
N Strips	0
X Bounds	-1.000e+00, 1.000e+00
Y Bounds	-1.000e+00, 1.000e+00
Z Bounds	-1.000e+00, 1.000e+00
N Arrays	0

Interior faces are marked by the tetgen.TetGen.triface_markers attribute. We can plot this using PyVista.

pl = pv.Plotter()
pl.add_mesh(
    trimesh.explode(0.3),
    scalars=tet.triface_markers,
    show_edges=True,
    show_scalar_bar=False,
)
pl.enable_ssao(radius=0.1)
pl.enable_anti_aliasing("ssaa")
pl.camera.zoom(1.5)
pl.show()

Interior faces are denoted with 0 and exterior faces are marked as -1 within the tetgen.TetGen.triface_markers array.

tet.triface_markers

array([ 0,  0,  0, -1,  0,  0,  0, -1,  0,  0,  0, -1,  0,  0,  0, -1,  0,
        0,  0, -1,  0,  0,  0, -1,  0,  0, -1, -1,  0,  0, -1,  0,  0, -1,
       -1,  0,  0, -1, -1,  0, -1,  0,  0, -1,  0,  0, -1,  0, -1,  0, -1,
        0,  0, -1,  0,  0, -1,  0,  0, -1,  0, -1,  0,  0, -1,  0, -1,  0,
        0,  0, -1,  0,  0, -1,  0, -1,  0, -1,  0,  0, -1,  0, -1,  0, -1,
        0,  0, -1,  0, -1,  0, -1,  0,  0, -1,  0,  0, -1,  0, -1,  0,  0,
       -1,  0,  0, -1,  0,  0, -1,  0, -1,  0,  0,  0, -1,  0,  0,  0, -1,
        0, -1,  0, -1,  0, -1,  0, -1,  0,  0, -1,  0,  0,  0, -1,  0, -1,
        0, -1,  0,  0, -1,  0,  0, -1, -1,  0,  0, -1,  0,  0, -1,  0, -1,
        0,  0,  0, -1, -1,  0,  0, -1,  0, -1,  0, -1,  0, -1,  0,  0, -1,
        0, -1, -1,  0,  0, -1,  0, -1,  0, -1,  0,  0, -1, -1,  0,  0, -1,
        0, -1, -1,  0, -1,  0, -1,  0, -1, -1,  0, -1, -1], dtype=int32)

Finally, create an edges pyvista.PolyData from the tetgen.TetGen.edges attribute.

# construct a VTK style edges array
n_edges = tet.edges.shape[0]
edges = np.empty((n_edges, 3), dtype=int)
edges[:, 0] = 2
edges[:, 1:] = tet.edges

# mesh containing both exterior and interior elements
edgemesh = pv.PolyData()
edgemesh.points = tet.node
edgemesh.lines = edges
edgemesh

PolyData	Information
N Cells	162
N Points	43
N Strips	0
X Bounds	-1.000e+00, 1.000e+00
Y Bounds	-1.000e+00, 1.000e+00
Z Bounds	-1.000e+00, 1.000e+00
N Arrays	0

Plot the edges with pyvista and color the interior and exterior edges.

edgemesh.plot(
    scalars=tet.edge_markers,
    cmap="bwr",
    line_width=10,
    render_lines_as_tubes=True,
    show_scalar_bar=False,
    zoom=1.5,
)