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="partial",        # Imprint shared surfaces
    imprint_threads="all",    # Keyword-only imprint thread count
    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

"partial", "full", None, or False

"partial"

Shared-surface imprint mode. None still imprints, with glue disabled; only False skips imprinting. See Imprinting for options.

imprint_threads

"all" or positive int

"all"

Keyword-only thread count for imprinting. See Imprinting for validation and scope.

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#