File Formats¶

mmgpy supports numerous file formats. The native Medit .mesh/.meshb reader and writer are registered with PyVista on import, so pv.read("foo.mesh") and dataset.save("foo.mesh") go through MMG's native I/O. Other formats are handled by PyVista directly. Formats not natively supported by VTK (e.g. .msh, .med, .inp) require pip install pyvista[io], which pulls in meshio.

Native MMG Format¶

The .mesh (ASCII) and .meshb (binary) formats are the native MMG formats and are recommended for best compatibility.

.mesh Format Structure¶

MeshVersionFormatted 2
Dimension 3

Vertices
4
0.0 0.0 0.0 0
1.0 0.0 0.0 0
0.0 1.0 0.0 0
0.0 0.0 1.0 0

Triangles
4
1 2 3 0
1 2 4 0
1 3 4 0
2 3 4 0

Tetrahedra
1
1 2 3 4 0

End

Supported Formats¶

Volume Mesh Formats (3D)¶

Surface Mesh Formats¶

2D Mesh Formats¶

Format Selection Guide¶

import pyvista as pv
import mmgpy  # noqa: F401  -- registers reader/writer + accessor

mesh = pv.read("input.mesh")

For MMG Processing¶

Use .mesh format:

mesh.save("output.mesh")

• Best compatibility with MMG
• Supports all MMG-specific features (ridges, required entities, reference markers)
• Companion .sol files are auto-loaded on read and round-trip via mesh.mmg.save_sol(...)

For Visualization (ParaView)¶

Use VTK formats:

mesh.save("output.vtk")   # Legacy
mesh.save("output.vtu")   # XML (preferred)

For CAD/3D Printing¶

Use STL:

import pyvista as pv
import mmgpy  # noqa: F401

# Surface meshes only
surface_mesh = pv.read("model.stl")
surface_mesh.save("output.stl")

For Other Software¶

Solution Files¶

MMG supports solution files (.sol / .solb) containing:

• Scalar fields (temperature, pressure, level set, isotropic metric)
• Vector fields (velocity, displacement)
• Tensor fields (stress, anisotropic metric)

When reading a .mesh / .meshb file, a sibling .sol (same stem, same directory) is auto-loaded into point_data / cell_data. The reserved keys metric, displacement, levelset, tensor are routed to MMG's solution channel on remesh.

Writing companion .sol files¶

import numpy as np
import pyvista as pv
import mmgpy  # noqa: F401

mesh = pv.read("input.mesh")

# Scalar field on vertices
mesh.point_data["temperature"] = np.random.rand(mesh.n_points)

# Save every numeric vertex / cell array as a multi-block `.sol`
mesh.mmg.save_all_sols("output.sol")

# Or write only the MMG-reserved fields (metric / displacement / ...) with save_sol
mesh.mmg.save_sol("output_metric.sol")

Loading solution files¶

import pyvista as pv
import mmgpy  # noqa: F401

mesh = pv.read("input.mesh")

# Attach extra fields from a separately-stored .sol
mesh.mmg.load_all_sols("input_fields.sol")

# Vertex-located arrays land in point_data; element-located arrays land in cell_data
if "temperature" in mesh.point_data:
    temp = mesh.point_data["temperature"]

Binary vs ASCII¶

# ASCII
mesh.save("output.mesh")

# Binary
mesh.save("output.meshb")

Format Detection¶

PyVista (and mmgpy's registered Medit reader) automatically detect the format from the file extension:

import pyvista as pv
import mmgpy  # noqa: F401

mesh = pv.read("model.stl")
mesh = pv.read("simulation.vtu")
mesh = pv.read("domain.msh")
mesh = pv.read("domain.mesh")  # Medit reader (provided by mmgpy)

Troubleshooting¶

Unsupported Format¶

If a format is not recognized:

1. Check the extension is correct.
2. Install pyvista[io] if the format is meshio-backed (.msh, .med, .inp, ...).
3. Try converting to .mesh or .vtk first.

Lost Data¶

Some formats do not support all features:

Large Files¶

For large meshes:

# Use binary format
mesh.save("large_mesh.meshb")

# Or compressed VTK
mesh.save("large_mesh.vtu")  # XML VTK supports compression