GMSH Mesh Files

GMSH Mesh Files#

Export meshes in GMSH’s native format for inspection, debugging, or further processing.

Basic Export#

import cadquery as cq
from cad_to_dagmc import CadToDagmc

assembly = cq.Assembly()
assembly.add(cq.Workplane("XY").sphere(10), name="sphere")

model = CadToDagmc()
model.add_cadquery_object(assembly, material_tags=["tungsten"])

# Export 2D surface mesh
model.export_gmsh_mesh_file(
    filename="surface_mesh.msh",
    dimensions=2,
    min_mesh_size=0.5,
    max_mesh_size=5.0,
)

# Export 3D volume mesh
model.export_gmsh_mesh_file(
    filename="volume_mesh.msh",
    dimensions=3,
    min_mesh_size=0.5,
    max_mesh_size=5.0,
)

With Per-Volume Mesh Sizing#

import cadquery as cq
from cad_to_dagmc import CadToDagmc

coarse_box = cq.Workplane().box(1, 1, 2)
fine_box = cq.Workplane().moveTo(1, 0.5).box(1, 1, 1.5)
default_box = cq.Workplane().moveTo(2, 1).box(1, 1, 1)

assembly = cq.Assembly()
assembly.add(coarse_box, name="coarse")
assembly.add(fine_box, name="fine")
assembly.add(default_box, name="global")

model = CadToDagmc()
model.add_cadquery_object(assembly, material_tags="assembly_names")

model.export_gmsh_mesh_file(
    filename="different_resolution_meshes.msh",
    dimensions=2,
    min_mesh_size=0.01,
    max_mesh_size=10,
    set_size={
        "coarse": 0.9,
        "fine": 0.1,
    },
)

API Reference#

export_gmsh_mesh_file()#

model.export_gmsh_mesh_file(
    filename="mesh.msh",      # Output file path
    dimensions=2,             # 2 for surface, 3 for volume
    min_mesh_size=1.0,        # Minimum element size
    max_mesh_size=10.0,       # Maximum element size
    mesh_algorithm=1,         # GMSH 2D surface algorithm
    mesh_algorithm_3d=1,      # GMSH 3D algorithm (1=Delaunay, 10=HXT)
    volume_mesh_options=None, # GMSH options applied only after surface meshing
    set_size=None,            # Per-volume sizes
    scale_factor=1.0,         # Geometry scaling
    imprint=True,             # Imprint shared surfaces
    method="file",            # CAD transfer method
)

Parameters:

Parameter

Type

Default

Description

filename

str

“mesh.msh”

Output GMSH file path

dimensions

int

2

Mesh dimensions (2=surface, 3=volume)

min_mesh_size

float

None

Minimum mesh element size

max_mesh_size

float

None

Maximum mesh element size

mesh_algorithm

int

1

GMSH 2D surface meshing algorithm

mesh_algorithm_3d

int

1

GMSH 3D volume algorithm: 1 = Delaunay, 10 = HXT

volume_mesh_options

dict

None

Numeric/string GMSH options applied after surface meshing, before volume meshing; only used with dimensions=3

set_size

dict

None

Per-volume mesh sizes

scale_factor

float

1.0

Geometry scale factor

imprint

bool or int

True

Imprint shared surfaces. An int limits the imprint to that many threads

method

str

“file”

CAD transfer method

For dimensions=3, mesh_algorithm_3d selects the volume algorithm independently of the surface algorithm. A non-empty volume_mesh_options dictionary causes surface generation first, followed by the option overrides and volume generation. dimensions=2 ignores these volume overrides. See 3D algorithms and volume-only options for examples and precedence rules.

Use Cases#

Debugging Mesh Quality#

Export to GMSH format and open in the GMSH GUI:

gmsh mesh.msh

This allows you to:

  • Visually inspect mesh quality

  • Check element sizes

  • Verify geometry import

Creating Pre-meshed Files#

Create a mesh file that can be converted to DAGMC later:

import cadquery as cq
from cad_to_dagmc import CadToDagmc
import cad_to_dagmc

# First, create GMSH mesh
result1 = cq.Workplane("XY").box(10.0, 10.0, 5.0)
result2 = cq.Workplane("XY").moveTo(10, 0).box(10.0, 10.0, 5.0)
assembly = cq.Assembly()
assembly.add(result1)
assembly.add(result2)
assembly.save("geometry.stp", exportType="STEP")

geometry = CadToDagmc()
geometry.add_stp_file("geometry.stp")
geometry.export_gmsh_mesh_file(filename="mesh.msh")

# Later, convert to DAGMC
cad_to_dagmc.export_gmsh_file_to_dagmc_h5m_file(
    gmsh_filename="mesh.msh",
    material_tags=["mat1", "mat2"],
    dagmc_filename="dagmc.h5m",
)

2D vs 3D Meshes#

Dimension

Mesh Type

Use Case

dimensions=2

Triangular surface

DAGMC geometry input

dimensions=3

Tetrahedral volume

Volume mesh / analysis

See Also#