TetGen#

.ele + .node read + write eager

Summary of the specification#

TetGen splits a mesh across sidecar files that share a basename. .node starts with a counts line - number of points, dimension, number of attributes, boundary-marker flag - then one line per point: an index, its coordinates, its attributes, and its marker if the flag is set. .ele starts with its own counts line - number of tetrahedra, nodes per tetrahedron, region-attribute flag - then one line per element: an index and its node indices, with an optional trailing region attribute. Indices may be 0- or 1-based; the first index in the file decides.

Specification at a glance#

.node header	npoints dim nattrs boundary_marker_flag
.node line	index x y z [attrs…] [marker]
.ele header	ntetrahedra nodes_per_tet region_attr_flag
.ele line	index n1 n2 n3 n4 [region]
index base	0 or 1, inferred from the first index
companions	.face, .edge, .neigh use the same convention

Read the full TetGen specification ↗

Reading#

import polyxios as px

mesh = px.read("model.ele")
mesh.vertices          # (n, 3)
mesh.element_types     # element groups found in the file

Writing#

px.write(mesh, "out.ele")

This codec takes no format-specific options.

Quirks worth knowing#

Pass either path - px.read("bar.ele") or px.read("bar.node") - and the paired file is located by basename.
Boundary markers become vertex tags and region attributes become element attributes, so both labelling schemes are kept. Those attributes are REALs in the format and are read as float64, so a fractional region value keeps its fraction.
Both 0- and 1-based indexing are handled; the base is inferred rather than assumed.
A .node file declaring 2 dimensions is padded with a zero z, so the vertex array is always (n, 3), and global_attrs["was_2d"] records the fact so the header goes back out declaring 2. A mesh whose vertices have since left the plane is written in three with a warning, and a mesh with tetrahedra to write keeps three whatever the flag says: the .ele file declares four nodes per element, and TetGen’s own 2-D mode fills the plane with triangles instead.