File Formats

mmgpy supports numerous file formats through its integration with 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)

Format	Extensions	Read	Write	Notes
MMG	.mesh, .meshb	Yes	Yes	Native, recommended
VTK Legacy	.vtk	Yes	Yes	Universal
VTK XML	.vtu	Yes	Yes	Modern VTK
GMSH	.msh	Yes	Yes	Popular for FEM
Abaqus	.inp	Yes	Yes	FEM
CGNS	.cgns	Yes	Yes	CFD
Exodus II	.e, .exo	Yes	Yes	Sandia
MED	.med	Yes	Yes	Salome
NASTRAN	.bdf, .nas	Yes	Limited	FEM

Surface Mesh Formats

Format	Extensions	Read	Write	Notes
STL	.stl	Yes	Yes	CAD export
OBJ	.obj	Yes	Yes	Graphics
PLY	.ply	Yes	Yes	Point cloud/mesh
OFF	.off	Yes	Yes	Simple format
VTK	.vtp	Yes	Yes	VTK polygonal

2D Mesh Formats

Format	Extensions	Read	Write	Notes
MMG	.mesh	Yes	Yes	Native
VTK	.vtk, .vtu	Yes	Yes	Universal
SVG	.svg	No	Yes	Visualization

Format Selection Guide

For MMG Processing

Use .mesh format:

mesh.save("output.mesh")

• Best compatibility with MMG
• Supports all MMG-specific features
• Can include solution/metric files

For Visualization (ParaView)

Use VTK formats:

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

For CAD/3D Printing

Use STL:

# Surface meshes only
mesh.save("output.stl")

For Other Software

Software	Recommended Format
ParaView	.vtu, .vtk
GMSH	.msh
Abaqus	.inp
Salome	.med
Blender	.obj, .stl, .ply
FreeCAD	.stl, .obj

Solution Files

MMG supports solution files (.sol) containing:

• Scalar fields (temperature, pressure)
• Vector fields (velocity, displacement)
• Tensor fields (stress, metric)

Creating Solution Files

import numpy as np

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

# Add scalar field
temperature = np.random.rand(mesh.get_mesh_size()["vertices"])
mesh["temperature"] = temperature

# Save mesh and solution
mesh.save("output.mesh")  # Also saves output.sol if fields exist

Loading Solution Files

# Solution file is loaded automatically if present
mesh = mmgpy.read("input.mesh")

# Access fields
if "temperature" in mesh:
    temp = mesh["temperature"]

Binary vs ASCII

Aspect	ASCII (.mesh)	Binary (.meshb)
File size	Larger	Smaller
Read speed	Slower	Faster
Human readable	Yes	No
Precision	Text representation	Full precision

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

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

Format Detection

mmgpy automatically detects format from extension:

# Auto-detected from extension
mesh = mmgpy.read("model.stl")
mesh = mmgpy.read("simulation.vtu")
mesh = mmgpy.read("domain.msh")

Troubleshooting

Unsupported Format

If a format is not recognized:

1. Check the extension is correct
2. Ensure meshio supports the format
3. Try converting to .mesh or .vtk first

Lost Data

Some formats don't support all features:

Data Type	.mesh	.vtk	.stl
Vertices	Yes	Yes	Yes
Triangles	Yes	Yes	Yes
Tetrahedra	Yes	Yes	No
Scalar fields	Via .sol	Yes	No
Vector fields	Via .sol	Yes	No
Material IDs	Yes	Yes	No

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