Tecplot (.dat, .tec)

The Tecplot ASCII data format: a VARIABLES list and one or more finite-element ZONEs. meshio++ only reads and writes a single FE zone.

Format name	tecplot
Extensions	.dat, .tec
Read / Write	✓ / ✓
Extra dependencies	—

Reading & writing

import meshioplusplus

mesh = meshioplusplus.read("field.dat")
meshioplusplus.tecplot.write("out.dat", mesh)

write takes no keyword arguments.

File structure

VARIABLES = "X" "Y" "Z" "phi" ...
ZONE T="..." N=<nodes> E=<elements> F=FEPOINT|FEBLOCK ET=TRIANGLE|... [VARLOCATION=([a-b]=CELLCENTERED)]
<data — layout depends on F/DATAPACKING and VARLOCATION>
<connectivity, 1-based>

VARIABLES supports multi-line continuation and quoted multi-word names (re-joined if a quoted name gets split across whitespace tokens); X/x and Y/y must be present or ReadError. ZONE header parsing tolerates multi-line continuation (it keeps reading as long as the next line's first token fails to parse as a float — i.e. as long as it still looks like header text) and handles a quoted zone title (T="...") plus either F= (accepts only FEPOINT/FEBLOCK) + ET=, or DATAPACKING=+ZONETYPE= (folded into an equivalent "FE" + DATAPACKING internal representation). Only the first zone in a file is read — the parser breaks immediately after it, silently ignoring any subsequent zones.

VARLOCATION=([a-b]=CELLCENTERED) (1-based, inclusive ranges, comma- separated [i] or [i-j] entries) marks which variables are cell-centered; without it, cell-centered-ness is instead inferred from NV= (a node- variable count — everything after it is cell-centered).

Data itself: FEBLOCK reads one variable's full array before moving to the next; FEPOINT reads one full-variable-tuple row per node. X/x (optionally Y/Z, case-insensitively) become point coordinates; everything else becomes point_data or cell_data per the location flags.

Cell types & node ordering

Tecplot zone type	meshio++
LINESEG / FELINESEG	line
TRIANGLE / FETRIANGLE	triangle
QUADRILATERAL / FEQUADRILATERAL	quad
TETRAHEDRON / FETETRAHEDRON	tetra
BRICK / FEBRICK	hexahedron

On write, pyramid/wedge/hexahedron all degrade to FEBRICK (8-node brick), padding with duplicated corner nodes as needed. Write-side node-order tables (used when the mesh has exactly one supported cell type):

type	order
pyramid	[0,1,2,3,4,4,4,4]
wedge	[0,1,4,3,2,2,5,5]

When the mesh has 2 or more cell types, all are degraded into a single FEQUADRILATERAL (if all 2D) or FEBRICK (if all 3D) zone using a slightly different padding table (triangle→[0,1,2,2], tetra→[0,1,2,2,3,3,3,3]; the degenerate-corner tables for pyramid/wedge/quad/hexahedron are unchanged). If the mesh mixes 2D and 3D cell types, the 2D cells are dropped entirely with a warning.

Data mapping

Point/cell variable names are used verbatim as point_data/cell_data keys (no tecplot: prefix); X/Y/Z (or lowercase) are reserved for coordinates and excluded from the data dicts.

Quirks & limitations

• Only the first zone in a multi-zone file is read; the rest are silently ignored, not merged or errored on.
• The multi-cell-type write path (degrading everything to one zone via the "order_2" tables) exists only in the Python writer — the C++ writer throws WriteError if more than one distinct cell type is present, which forces the Python fallback for any such mesh.
• Data columns are wrapped at 20 values per line on write.

Notes

• tests/meshes/tecplot/quad_zone_comma.tec / quad_zone_space.tec / quad_zone_multivar.tec — a single quad zone (N=4, E=1, ET=QUADRILATERAL), FEBLOCK packing, one cell-centered variable via VARLOCATION=([4]=CELLCENTERED); the three files vary the delimiter style around zone-header keys (comma vs. plain space vs. an extra variable) to exercise the tolerant zone-header parser. quad_zone_space.tec in particular has a zone title that is literally the string "VARLOCATION" with spaced = signs — an adversarial case the C++ reader throws on cleanly, letting the Python reader take over.
• The C++ core handles single-zone FE meshes (BLOCK/POINT packing, VARLOCATION).