FEM_TO_GMSH
Convert Mesh Data from FEM to GMSH Format

FEM_TO_GMSH is a C++ program which converts FEM files representing a 1D, 2D, or 3D mesh into a GMSH mesh file.

The FEM files include a node file, which simply lists the coordinates of each node, and an element connectivity file, which lists, for each element, the indices of the nodes that define it. Either 0 or 1-based indexing can be used when referencing the nodes.

Usage:

fem_to_gmsh prefix

• 'prefix'_nodes.txt contains the node coordinates,
• 'prefix'_elements.txt contains the element node connectivity.
• 'prefix'.msh will contain the Gmsh mesh file.

Licensing:

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

Languages:

FEM_TO_GMSH is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.

Related Data and Programs:

DOLFIN-CONVERT, a Python program which can convert mesh file from Gmsh, MEDIT, METIS or SCOTCH format to an XML format suitable for use by DOLFIN or FENICS, by Anders Logg.

FEM_TO_MEDIT, a C++ program which reads a pair of FEM files defining node coordinates and elements, and creates a corresponding MEDIT mesh file.

FEM_TO_TRIANGLE, a C++ program which reads FEM files defining a 2D mesh of triangles, namely a file of node coordinates and a file of elements defined by node indices, and creates a corresponding pair of node and element files for use by Jonathan Shewchuk's triangle program.

FEM_TO_XML, a C++ program which reads FEM files defining a 1D, 2D or 3D mesh, namely a file of node coordinates and a file of elements defined by node indices, and creates a corresponding XML file for input to DOLFIN or FENICS.

GMSH, examples which illustrate the use of the Gmsh program, a 3D mesh generator for the finite element method (FEM).

GMSH_IO, a C++ library which can read or write some of the files created by the Gmsh program for 1D, 2D or 3D meshes used by the finite element method (FEM).

GMSH_TO_FEM, a C++ program which reads a mesh data file created by the GMSH program and writes a pair of node and element files that correspond to the FEM format.

MSH, a data directory of examples of MSH files, the native 3D mesh format used by Gmsh.

Reference:

1. Christophe Geuzaine, Jean-Francois Remacle,
   Gmsh: a three-dimensional finite element mesh generator with built-in pre- and post-processing facilities,
   International Journal for Numerical Methods in Engineering,
   Volume 79, Number 11, pages 1309-1331, 2009.

Source Code:

• fem_to_gmsh.cpp, the source code.
• fem_to_gmsh.sh, commands to compile the source code.

Examples and Tests:

CHEBY9 is a 1D interval, [-1,+1], containing 9 nodes and 8 elements.

• cheby9_nodes.txt, the node coordinates.
• cheby9_elements.txt, the elements.
• cheby9.msh, the corresponding GMSH mesh file.

MESH3D is a 3D tetrahedral mesh using 8 nodes and 6 elements.

• mesh3d_nodes.txt, the nodes for the 4-node tet mesh.
• mesh3d_elements.txt, the elements for the 4-node tet mesh.
• mesh3d.msh, the Gmsh msh file version of the data.

RECTANGLE is a 2D rectangular region which has been divided into 3 rows and 4 columns of squares, each then split into two 3-node triangles. The node and element files of this triangulation are converted into a Gmsh msh file describing the same triangulation.

• rectangle_nodes.txt, the node coordinates.
• rectangle_elements.txt, the elements.
• rectangle.png, a PNG image of the triangulation, created by TRIANGULATION_PLOT.
• rectangle.msh, the corresponding Gmsh msh file.

List of Routines:

• MAIN is the main program for FEM_TO_GMSH.
• CH_CAP capitalizes a single character.
• CH_EQI is a case insensitive comparison of two characters for equality.
• CH_TO_DIGIT returns the value of a base 10 digit.
• FILE_COLUMN_COUNT counts the number of columns in the first line of a file.
• FILE_ROW_COUNT counts the number of row records in a file.
• GET_UNIT returns a free FORTRAN unit number.
• GMSH_WRITE writes the triangulation data as a Gmsh mesh file.
• I4MAT_DATA_READ reads data from an I4MAT file.
• I4MAT_HEADER_READ reads the header from an I4MAT.
• I4MAT_TRANSPOSE_PRINT prints an I4MAT, transposed.
• I4MAT_TRANSPOSE_PRINT_SOME prints some of the transpose of an I4MAT.
• MESH_BASE_ONE ensures that the element definition is one-based.
• R8MAT_DATA_READ reads data from an R8MAT file.
• R8MAT_HEADER_READ reads the header from an R8MAT file.
• R8MAT_TRANSPOSE_PRINT prints an R8MAT, transposed.
• R8MAT_TRANSPOSE_PRINT_SOME prints some of an R8MAT, transposed.
• S_TO_I4 reads an I4 from a string.
• S_TO_I4VEC reads an I4VEC from a string.
• S_TO_R8 reads an R8 from a string.
• S_TO_R8VEC reads an R8VEC from a string.
• S_WORD_COUNT counts the number of "words" in a string.
• TIMESTAMP prints the current YMDHMS date as a time stamp.

You can go up one level to the C++ source codes.