FLAC3D#

.f3grid read + write eager

Summary of the specification#

.f3grid is Itasca’s ASCII grid exchange file. Records are keyword-led: G (or GRIDPOINT) lines declare a gridpoint id and its coordinates, Z lines declare a zone with a shape keyword (B8, W6, P5, T4) and its gridpoint ids, and F lines declare surface faces. ZGROUP and FGROUP records name a group and list the zone or face ids that belong to it, which is how regions and boundaries are carried.

Specification at a glance#

gridpoints	G <id> <x> <y> <z>
zones	Z <shape> <id> <gp ids…> — B8 hex, W6 wedge, P5 pyramid, T4 tet
faces	F <shape> <id> <gp ids…>
groups	ZGROUP / FGROUP <name> followed by member ids
comments	lines starting with *

Read the full FLAC3D specification ↗

Reading#

import polyxios as px

mesh = px.read("model.f3grid")
mesh.vertices          # (n, 3)
mesh.element_types     # element groups found in the file

Writing#

px.write(mesh, "out.f3grid")

This codec takes no format-specific options.

Quirks worth knowing#

Both zones and faces are read, so a file’s volume mesh and its boundary surface arrive as separate element groups.
ZGROUP and FGROUP names become element tags; a zone in several groups stays in all of them.
Gridpoint ids are sparse in practice and are remapped to a dense 0-based index on read.