Tecplot SZL (.szplt)

Tecplot's subzone-loadable format, the default output of Tecplot 360 since 2016 and of TecIO-based solvers (SU2, FUN3D…). It is undocumented, and TecIO, Tecplot's own library, is its only reader, so meshio++ reads it through a TecIO the user already has. New in v16.13.0; written too since the writer joined.

Format name	szplt
Extensions	.szplt (also found by content, #!SZPLT)
Read / Write	✓ / ✓ (conformance)
Time steps	✓ — as Tecplot: the distinct solution times
Extra dependencies	TecIO: a core built with MESHIOPLUSPLUS_WITH_TECIO=ON, or a shared TecIO named by MESHIOPLUSPLUS_TECIO_LIBRARY

Reading

import meshioplusplus

mesh = meshioplusplus.read("flow.szplt")
last = meshioplusplus.read("flow.szplt", time_step=-1)
meshioplusplus.szplt.time_values("flow.szplt")

A .szplt reads exactly as the same data saved as .plt or .dat does: TecIO's reader fills the zone model the ASCII and binary Tecplot readers share, so zones, regions, point and cell data, variable sharing, passive variables, shared connectivity and time steps follow Tecplot. FEPOLYGON and FEPOLYHEDRON zones are refused by name (save such a file as .plt): TecIO 2018.3, the version the tests run, refuses to write them in an SZL file ("Polygon and Polyhedral zones are currently not supported by SZL files"), so there is no file to check a reader against, and the face-based zones stay with the .plt and ASCII readers. A newer TecIO, and a .szplt written by Tecplot 360 with such zones, join the roadmap.

Writing

meshioplusplus.write("flow.szplt", mesh)                                   # a static data set
meshioplusplus.write_sequence("flow.szplt", steps, file_format="szplt")   # a strand of zones per step

meshioplusplus convert model.vtu model.szplt

TecIO writes the file, in the layout the ASCII and .plt writers use: one zone per cell block (named after a cell region that is exactly the block, else block_<i>), X, Y, (Z) and the point data as nodal variables, cell data as cell-centred variables (a variable a block has no values for is passive in its zone), vector and tensor arrays split into <name>_<k>. Each variable is written in the TecIO type that holds its array's dtype exactly: float32 stays single precision, int16 and int8 are 16-bit, uint8 is a byte, int32 and uint16 are 32-bit, and what no TecIO type holds (float64, 64-bit integers, unsigned 32- and 64-bit) is a double; the coordinates take the points' type. The readers return every type as float64, so a read is value-equal. A wedge or pyramid is a degenerate brick and comes back as a hexahedron, as in .plt; vertices and polygon or polyhedron blocks are skipped with a warning. TecIO shares a variable between zones only together with their connectivity, so the blocks of one mesh cannot share a point array as they do in the other Tecplot writers: a mesh of one block is one zone with every point, and a mesh of several gives each zone the points its cells use (a point several blocks use is repeated, one no cell uses is dropped), as TecIO's own files have it. A static file's tetrahedron and brick zones whose cells carry partition:part values of several parts (the partitioner's cell array) are written as partitioned zones, one partition per part: a partition holds the nodes its cells use, the lowest part to use a node owns it and the others hold it as a ghost node, and the nodes no cell uses are the first part's. TecIO joins the partitions into one zone when it reads, numbering the nodes partition by partition (each part's owned nodes in order) and the cells by part, so the mesh reads back with its points permuted and its cells grouped by part, every cell and value intact; the partition:part array is written as a cell variable like any other. TecIO takes partitions of three-dimensional FE zones only, and refuses a part that owns no node of its own (a part whose nodes all belong to lower parts): such a zone is written whole, with a warning. A series is written whole as well, since a zone that shares its connectivity from a partitioned one would need the partitions again. A series is a strand (STRANDID 1) of zones per step at the step's time, the later steps sharing the first step's coordinates and connectivity, so every step needs the first step's points and cells and the same variables. The core built with TecIO and the Python twin through MESHIOPLUSPLUS_TECIO_LIBRARY write the same zones; they are never loaded together, since the twin needs a second, shared TecIO.

Getting TecIO

meshio++ never redistributes TecIO. Two ways to point it at yours:

• A native build with -DMESHIOPLUSPLUS_WITH_TECIO=ON -DTECIO_ROOT=<dir>, where <dir> holds TECIO.h (with tecio_Exports.h and StandardIntegralTypes.h) and libtecio — a static libtecio.a also needs pthread, which the build adds. This is what the C, Fortran, Julia and R bindings and the native CLI read through. TecIO is the source Tecplot distributes on its TecIO page (free, a registration form), or the copy a Tecplot 360 install carries; build/configure.sh --with-tecio <dir> sets both flags.
• The Python reader loads a shared TecIO through ctypes: set MESHIOPLUSPLUS_TECIO_LIBRARY to its path (Tecplot 360 ships libtecio.so / tecio.dll in its bin directory), or have it on the library search path. TecIO's own CMake builds a static library with hidden symbols; for a shared one, build it with add_library(tecio SHARED …) and without -fvisibility=hidden.

Without either, reading raises an ImportError naming both and the third way: save the file as .plt in Tecplot (Tecplot route).

Validation

The fixtures (tests/python/meshes/szplt) are written by TecIO 2018.3 — the TecIO source SU2 vendors — each beside an ASCII twin holding the same data: two FE zones of tetrahedra and bricks with cell-centred data, an ordered zone, a transient file sharing variables and connectivity with passive variables, and single-precision triangles. Both engines read every .szplt identically to its twin. A .szplt written by Tecplot 360 itself is listed in the roadmap.