FREEFEM++_MSH_IO
Read and Write FreeFem++ MSH files

FREEFEM++_MSH_IO, a Python library which can read and write files used by the FreeFem++ finite element program to store mesh information.

Note that the GMSH program creates mesh files that use the ".msh" extension, but which are an entirely different format.

The msh file format is obliquely described in section 12.5 of the FreeFem++ documentation.

At least for the 2D case of a triangular mesh, the format seems to be as follows:

a single line giving NV, NE, NT, the number of vertices, boundary edges, and triangles
NV lines, each containing the (X,Y) coordinates and integer label for a node.
NT lines, each containing three vertex indices and integer label for a triangle.
NE lines, each containing two vertex indices and integer label for a boundary edge.

The "labels" seem to be "0" for interior objects and 1 for boundary objects. All edges are boundary objects. (This might not be true. A geometry might include internal edges, and perhaps these count as interior objects, but definitely, the edge list does not include arbitrary triangle edges, only those on the boundary.) All triangles are interior objects. Vertices may be boundary or interior objects.

Licensing:

The computer code and data files made available on this web page are distributed under the GNU LGPL license.

Languages:

FREEFEM++_MSH_IO is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version and a Python version.

Related Data and Programs:

BAMG, examples which illustrate the use of BAMG, a program for generating 2D meshes that can be used to define the geometry for the the finite element package FREEFEM++.

FREEFEM++, examples which illustrate the use of the FREEFEM++ package, a high-level integrated development environment for the numerical solution of nonlinear multiphysics partial differential equations (PDE's) in 2D and 3D.

FREEFEM++_MSH, a data directory which contains examples of the mesh files created by the FreeFem++ program, which use the extension ".msh".

MITCHELL_FREEFEM++, examples which illustrate the implementation of the Mitchell 2D elliptic partial differential equation (PDE) test problems using FREEFEM++.

Reference:

Frederic Hecht,
New development in FreeFem++,
Journal of Numerical Mathematics,
Volume 20, Number 3-4, 2012, pages 251-265.
Frederic Hecht,
BAMG: Bidimensional Anisotropic Mesh Generator,
draft version v1.00, December 2006.

Source Code:

freefem++_msh_io.py, the source code.
freefem++_msh_io_test.sh, BASH commands to run the sample program.
freefem++_msh_io_test.txt, the output file.
input.msh, a FreeFem++ file read by the program.
output.msh, a FreeFem++ file written by the program.

List of Routines:

FFMSH_2D_DATA_EXAMPLE returns example FFMSH data.
FFMSH_2D_DATA_PRINT prints FFMSH data.
FFMSH_2D_DATA_READ reads data from an FFMSH file.
FFMSH_2D_SIZE_EXAMPLE returns sizes for the 2D example.
FFMSH_2D_SIZE_PRINT prints the sizes of an FFMSH.
FFMSH_2D_SIZE_READ reads sizes from a FFMSH file.
FFMSH_2D_WRITE writes FFMSH data to a file.
I4MAT_TRANSPOSE_PRINT prints an I4MAT, transposed.
I4MAT_TRANSPOSE_PRINT_SOME prints some of the transpose of an I4MAT.
I4VEC_PRINT prints an I4VEC.
R8MAT_TRANSPOSE_PRINT prints an R8MAT, transposed.
R8MAT_TRANSPOSE_PRINT_SOME prints some of an R8MAT, transposed.
TIMESTAMP prints the current YMDHMS date as a time stamp.

You can go up one level to the Python source codes.

Last revised on 05 January 2015.