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This chapter describes Gmsh's native "MSH" file format, used to store meshes and associated post-processing datasets. The MSH format exists in two flavors: ASCII and binary. The format has a version number (currently: 2.0) that is independent of Gmsh's main version number.
9.1 MSH ASCII file format 9.2 MSH binary file format 9.3 Node ordering 9.4 Legacy formats
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The MSH ASCII file format contains one mandatory section giving
information about the file ($MeshFormat
), followed by several
optional sections defining the nodes ($Nodes
), elements
($Elements
), region names ($PhysicalName
) and
post-processing datasets ($NodeData
, $ElementData
,
$ElementNodeData
). Sections can be repeated in the same file, and
post-processing sections can be put into separate files (e.g. one file
per time step).
The format is defined as follows:
$MeshFormat version-number file-type data-size $EndMeshFormat $Nodes number-of-nodes node-number x-coord y-coord z-coord ... $EndNodes $Elements number-of-elements elm-number elm-type number-of-tags < tag > ... node-number-list ... $EndElements $PhysicalNames number-of-names phyical-number "physical-name" ... $EndPhysicalNames $NodeData number-of-string-tags < "string-tag" > ... number-of-real-tags < real-tag > ... number-of-integer-tags < integer-tag > ... node-number value ... ... $EndNodeData $ElementData number-of-string-tags < "string-tag" > ... number-of-real-tags < real-tag > ... number-of-integer-tags < integer-tag > ... elm-number value ... ... $EndElementData $ElementNodeData number-of-string-tags < "string-tag" > ... number-of-real-tags < real-tag > ... number-of-integer-tags < integer-tag > ... elm-number number-of-nodes-per-element value ... ... $ElementEndNodeData |
where
version-number
file-type
data-size
number-of-nodes
node-number
x-coord y-coord z-coord
number-of-elements
elm-number
elm-type
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
number-of-tags
node-number-list
number-of-string-tags
number-of-real-tags
number-of-integer-tags
number-of-nodes-per-elements
value
NodeData
(respectively ElementData
) views,
there are ncomp values per node (resp. per element), where
ncomp is the number of field components. For
ElementNodeData
views, there are ncomp times
number-of-nodes-per-elements values per element.
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The binary file format is similar to the ASCII format described above:
$MeshFormat version-number file-type data-size one-binary $EndMeshFormat $Nodes number-of-nodes nodes-binary $EndNodes $Elements number-of-elements element-header-binary elements-binary element-header-binary elements-binary ... $EndElements [ all other sections are identical to ASCII, except that node-number, elm-number, number-of-nodes-per-element and values are written in binary format ] |
where
version-number
file-type
data-size
one-binary
Here is a pseudo C code to write one-binary:
int one = 1; fwrite(&one, sizeof(int), 1, file); |
number-of-nodes
nodes-binary
Here is a pseudo C code to write nodes-binary:
for(i = 0; i < number_of_nodes; i++){ fwrite(&num_i, sizeof(int), 1, file); double xyz[3] = {node_i_x, node_i_y, node_i_z}; fwrite(&xyz, sizeof(double), 3, file); } |
number-of-elements
element-header-binary
Here is a pseudo C code to write element-header-binary:
int header[3] = {elm_type, num_elm_follow, num_tags}; fwrite(&header, sizeof(int), 3, file); |
elements-binary
Here is a pseudo C code to write elements-binary for triangles with the 3 standard tags (the physical and elementary regions, and the mesh partition):
for(i = 0; i < number_of_triangles; i++){ int data[7] = {num_i, physical, elementary, partition, node_i_1, node_i_2, node_i_3}; fwrite(data, sizeof(int), 7, file); } |
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For all mesh and post-processing file formats, the reference elements are defined as follows.
Line: Line3: 0----------1 --> u 0-----2----1 |
Triangle: Triangle6: v ^ | 2 2 |`\ |`\ | `\ | `\ | `\ 5 `4 | `\ | `\ | `\ | `\ 0----------1 --> u 0-----3----1 |
Quadrangle: Quadrangle8: Quadrangle9: v ^ | 3-----------2 3-----6-----2 3-----6-----2 | | | | | | | | | | | | | | | +---- | --> u 7 5 7 8 5 | | | | | | | | | | | | 0-----------1 0-----4-----1 0-----4-----1 |
Tetrahedron: Tetrahedron10: v . ,/ / 2 2 ,/|`\ ,/|`\ ,/ | `\ ,/ | `\ ,/ '. `\ ,6 '. `5 ,/ | `\ ,/ 8 `\ ,/ | `\ ,/ | `\ 0-----------'.--------1 --> u 0--------4--'.--------1 `\. | ,/ `\. | ,/ `\. | ,/ `\. | ,9 `\. '. ,/ `7. '. ,/ `\. |/ `\. |/ `3 `3 `\. ` w |
Hexahedron: Hexahedron20: Hexahedron27: v 3----------2 3----13----2 3----13----2 |\ ^ |\ |\ |\ |\ |\ | \ | | \ | 15 | 14 |15 24 | 14 | \ | | \ 9 \ 11 \ 9 \ 20 11 \ | 7------+---6 | 7----19+---6 | 7----19+---6 | | +-- |-- | -> u | | | | |22 | 26 | 23| 0---+---\--1 | 0---+-8----1 | 0---+-8----1 | \ | \ \ | \ 17 \ 18 \ 17 25 \ 18 \ | \ \ | 10 | 12| 10 | 21 12| \| w \| \| \| \| \| 4----------5 4----16----5 4----16----5 |
Prism: Prism15: Prism18: w ^ | 3 3 3 ,/|`\ ,/|`\ ,/|`\ ,/ | `\ 12 | 13 12 | 13 ,/ | `\ ,/ | `\ ,/ | `\ 4------+------5 4------14-----5 4------14-----5 | | | | 8 | | 8 | | ,/|`\ | | | | | ,/|`\ | | ,/ | `\ | | | | | 15 | 16 | |,/ | `\| | | | |,/ | `\| ,| | `\ 10 | 11 10-----17-----11 ,/ | 0 | `\ | 0 | | 0 | u | ,/ `\ | v | ,/ `\ | | ,/ `\ | | ,/ `\ | | ,6 `7 | | ,6 `7 | |,/ `\| |,/ `\| |,/ `\| 1-------------2 1------9------2 1------9------2 |
Pyramid: Pyramid13: Pyramid14: 4 4 4 ,/|\ ,/|\ ,/|\ ,/ .'|\ ,/ .'|\ ,/ .'|\ ,/ | | \ ,/ | | \ ,/ | | \ ,/ .' | `. ,/ .' | `. ,/ .' | `. ,/ | '. \ ,7 | 12 \ ,7 | 12 \ ,/ .' w | \ ,/ .' | \ ,/ .' | \ ,/ | ^ | \ ,/ 9 | 11 ,/ 9 | 11 0----------.'--|-3 `. 0--------6-.'----3 `. 0--------6-.'----3 `. `\ | | `\ \ `\ | `\ \ `\ | `\ \ `\ .' +----`\ - \ -> v `5 .' 10 \ `5 .' 13 10 \ `\ | `\ `\ \ `\ | `\ \ `\ | `\ \ `\.' `\ `\` `\.' `\` `\.' `\` 1----------------2 1--------8-------2 1--------8-------2 `\ u |
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This section describes Gmsh's older native file formats. Future versions of Gmsh will continue to support these formats, but we recommend that you do not use them in new aplications.
9.4.1 MSH file format version 1.0 9.4.2 POS ASCII file format 9.4.3 POS binary file format
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The MSH file format version 1.0 is Gmsh's old native mesh file format, now superseded by the format described in 9.1 MSH ASCII file format. It is defined as follows:
$NOD number-of-nodes node-number x-coord y-coord z-coord ... $ENDNOD $ELM number-of-elements elm-number elm-type reg-phys reg-elem number-of-nodes node-number-list ... $ENDELM |
where
number-of-nodes
node-number
x-coord y-coord z-coord
number-of-elements
elm-number
elm-type
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
reg-phys
reg-elem
number-of-nodes
node-number-list
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The POS ASCII file is Gmsh's old native pot-processing format, now superseded by the format described in 9.1 MSH ASCII file format. It is defined as follows:
$PostFormat 1.4 file-type data-size $EndPostFormat $View view-name nb-time-steps nb-scalar-points nb-vector-points nb-tensor-points nb-scalar-lines nb-vector-lines nb-tensor-lines nb-scalar-triangles nb-vector-triangles nb-tensor-triangles nb-scalar-quadrangles nb-vector-quadrangles nb-tensor-quadrangles nb-scalar-tetrahedra nb-vector-tetrahedra nb-tensor-tetrahedra nb-scalar-hexahedra nb-vector-hexahedra nb-tensor-hexahedra nb-scalar-prisms nb-vector-prisms nb-tensor-prisms nb-scalar-pyramids nb-vector-pyramids nb-tensor-pyramids nb-scalar-lines2 nb-vector-lines2 nb-tensor-lines2 nb-scalar-triangles2 nb-vector-triangles2 nb-tensor-triangles2 nb-scalar-quadrangles2 nb-vector-quadrangles2 nb-tensor-quadrangles2 nb-scalar-tetrahedra2 nb-vector-tetrahedra2 nb-tensor-tetrahedra2 nb-scalar-hexahedra2 nb-vector-hexahedra2 nb-tensor-hexahedra2 nb-scalar-prisms2 nb-vector-prisms2 nb-tensor-prisms2 nb-scalar-pyramids2 nb-vector-pyramids2 nb-tensor-pyramids2 nb-text2d nb-text2d-chars nb-text3d nb-text3d-chars time-step-values < scalar-point-value > ... < vector-point-value > ... < tensor-point-value > ... < scalar-line-value > ... < vector-line-value > ... < tensor-line-value > ... < scalar-triangle-value > ... < vector-triangle-value > ... < tensor-triangle-value > ... < scalar-quadrangle-value > ... < vector-quadrangle-value > ... < tensor-quadrangle-value > ... < scalar-tetrahedron-value > ... < vector-tetrahedron-value > ... < tensor-tetrahedron-value > ... < scalar-hexahedron-value > ... < vector-hexahedron-value > ... < tensor-hexahedron-value > ... < scalar-prism-value > ... < vector-prism-value > ... < tensor-prism-value > ... < scalar-pyramid-value > ... < vector-pyramid-value > ... < tensor-pyramid-value > ... < scalar-line2-value > ... < vector-line2-value > ... < tensor-line2-value > ... < scalar-triangle2-value > ... < vector-triangle2-value > ... < tensor-triangle2-value > ... < scalar-quadrangle2-value > ... < vector-quadrangle2-value > ... < tensor-quadrangle2-value > ... < scalar-tetrahedron2-value > ... < vector-tetrahedron2-value > ... < tensor-tetrahedron2-value > ... < scalar-hexahedron2-value > ... < vector-hexahedron2-value > ... < tensor-hexahedron2-value > ... < scalar-prism2-value > ... < vector-prism2-value > ... < tensor-prism2-value > ... < scalar-pyramid2-value > ... < vector-pyramid2-value > ... < tensor-pyramid2-value > ... < text2d > ... < text2d-chars > ... < text3d > ... < text3d-chars > ... $EndView |
where
file-type
data-size
view-name
nb-time-steps
nb-scalar-points
nb-vector-points
...
nb-text2d
nb-text3d
nb-text2d-chars
nb-text3d-chars
time-step-values
scalar-point-value
vector-point-value
...
For example, vector-triangle-value is defined as:
coord1-node1 coord1-node2 coord1-node3 coord2-node1 coord2-node2 coord2-node3 coord3-node1 coord3-node2 coord3-node3 comp1-node1-time1 comp2-node1-time1 comp3-node1-time1 comp1-node2-time1 comp2-node2-time1 comp3-node2-time1 comp1-node3-time1 comp2-node3-time1 comp3-node3-time1 comp1-node1-time2 comp2-node1-time2 comp3-node1-time2 comp1-node2-time2 comp2-node2-time2 comp3-node2-time2 comp1-node3-time2 comp2-node3-time2 comp3-node3-time2 ... |
The ordering of the nodes is given in 9.3 Node ordering.
text2d
coord1 coord2 style index |
text2d-chars
\0
' character.
text3d
coord1 coord2 coord3 style index |
text3d-chars
\0
' character.
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The POS binary file format is the same as the POS ASCII file format described in 9.4.2 POS ASCII file format, except that:
Here is a pseudo C code to write a post-processing file in binary format:
int one = 1; fprintf(file, "$PostFormat\n"); fprintf(file, "%g %d %d\n", 1.4, 1, sizeof(double)); fprintf(file, "$EndPostFormat\n"); fprintf(file, "$View\n"); fprintf(file, "%s %d " "%d %d %d %d %d %d %d %d %d " "%d %d %d %d %d %d %d %d %d " "%d %d %d %d %d %d %d %d %d " "%d %d %d %d %d %d %d %d %d " "%d %d %d %d %d %d %d %d %d " "%d %d %d %d\n", view-name, nb-time-steps, nb-scalar-points, nb-vector-points, nb-tensor-points, nb-scalar-lines, nb-vector-lines, nb-tensor-lines, nb-scalar-triangles, nb-vector-triangles, nb-tensor-triangles, nb-scalar-quadrangles, nb-vector-quadrangles, nb-tensor-quadrangles, nb-scalar-tetrahedra, nb-vector-tetrahedra, nb-tensor-tetrahedra, nb-scalar-hexahedra, nb-vector-hexahedra, nb-tensor-hexahedra, nb-scalar-prisms, nb-vector-prisms, nb-tensor-prisms, nb-scalar-pyramids, nb-vector-pyramids, nb-tensor-pyramids, nb-scalar-lines2, nb-vector-lines2, nb-tensor-lines2, nb-scalar-triangles2, nb-vector-triangles2, nb-tensor-triangles2, nb-scalar-quadrangles2, nb-vector-quadrangles2, nb-tensor-quadrangles2, nb-scalar-tetrahedra2, nb-vector-tetrahedra2, nb-tensor-tetrahedra2, nb-scalar-hexahedra2, nb-vector-hexahedra2, nb-tensor-hexahedra2, nb-scalar-prisms2, nb-vector-prisms2, nb-tensor-prisms2, nb-scalar-pyramids2, nb-vector-pyramids2, nb-tensor-pyramids2, nb-text2d, nb-text2d-chars, nb-text3d, nb-text3d-chars); fwrite(&one, sizeof(int), 1, file); fwrite(time-step-values, sizeof(double), nb-time-steps, file); fwrite(all-scalar-point-values, sizeof(double), ..., file); ... fprintf(file, "\n$EndView\n"); |
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