Pygmsh
:spider_web: Gmsh for Python
Install / Use
/learn @nschloe/PygmshREADME
pygmsh combines the power of Gmsh with the versatility of Python. It provides useful abstractions from Gmsh's own Python interface so you can create complex geometries more easily.
To use, install Gmsh itself and pygmsh from pypi:
[sudo] apt install python3-gmsh
pip install pygmsh
This document and the tests/
directory contain many small examples. See
here for the full documentation.
Flat shapes
| <img src="https://nschloe.github.io/pygmsh/polygon.svg" width="100%"> | <img src="https://nschloe.github.io/pygmsh/circle.svg" width="100%"> | <img src="https://nschloe.github.io/pygmsh/splines.svg" width="100%"> | | :-------------------------------------------------------------------: | :------------------------------------------------------------------: | :-------------------------------------------------------------------: | | Polygon | Circle | (B-)Splines |
Codes:
import pygmsh
with pygmsh.geo.Geometry() as geom:
geom.add_polygon(
[
[0.0, 0.0],
[1.0, -0.2],
[1.1, 1.2],
[0.1, 0.7],
],
mesh_size=0.1,
)
mesh = geom.generate_mesh()
# mesh.points, mesh.cells, ...
# mesh.write("out.vtk")
import pygmsh
with pygmsh.geo.Geometry() as geom:
geom.add_circle([0.0, 0.0], 1.0, mesh_size=0.2)
mesh = geom.generate_mesh()
import pygmsh
with pygmsh.geo.Geometry() as geom:
lcar = 0.1
p1 = geom.add_point([0.0, 0.0], lcar)
p2 = geom.add_point([1.0, 0.0], lcar)
p3 = geom.add_point([1.0, 0.5], lcar)
p4 = geom.add_point([1.0, 1.0], lcar)
s1 = geom.add_bspline([p1, p2, p3, p4])
p2 = geom.add_point([0.0, 1.0], lcar)
p3 = geom.add_point([0.5, 1.0], lcar)
s2 = geom.add_spline([p4, p3, p2, p1])
ll = geom.add_curve_loop([s1, s2])
pl = geom.add_plane_surface(ll)
mesh = geom.generate_mesh()
The return value is always a meshio mesh, so to store it to a file you can
<!--pytest-codeblocks:skip-->mesh.write("test.vtk")
The output file can be visualized with various tools, e.g., ParaView.
With
<!--pytest-codeblocks:skip-->pygmsh.write("test.msh")
you can access Gmsh's native file writer.
Extrusions
| <img src="https://nschloe.github.io/pygmsh/extrude.png" width="100%"> | <img src="https://nschloe.github.io/pygmsh/revolve.png" width="100%"> | <img src="https://nschloe.github.io/pygmsh/twist.png" width="100%"> |
| :-------------------------------------------------------------------: | :-------------------------------------------------------------------: | :-----------------------------------------------------------------: |
| extrude | revolve | twist |
import pygmsh
with pygmsh.geo.Geometry() as geom:
poly = geom.add_polygon(
[
[0.0, 0.0],
[1.0, -0.2],
[1.1, 1.2],
[0.1, 0.7],
],
mesh_size=0.1,
)
geom.extrude(poly, [0.0, 0.3, 1.0], num_layers=5)
mesh = geom.generate_mesh()
from math import pi
import pygmsh
with pygmsh.geo.Geometry() as geom:
poly = geom.add_polygon(
[
[0.0, 0.2, 0.0],
[0.0, 1.2, 0.0],
[0.0, 1.2, 1.0],
],
mesh_size=0.1,
)
geom.revolve(poly, [0.0, 0.0, 1.0], [0.0, 0.0, 0.0], 0.8 * pi)
mesh = geom.generate_mesh()
from math import pi
import pygmsh
with pygmsh.geo.Geometry() as geom:
poly = geom.add_polygon(
[
[+0.0, +0.5],
[-0.1, +0.1],
[-0.5, +0.0],
[-0.1, -0.1],
[+0.0, -0.5],
[+0.1, -0.1],
[+0.5, +0.0],
[+0.1, +0.1],
],
mesh_size=0.05,
)
geom.twist(
poly,
translation_axis=[0, 0, 1],
rotation_axis=[0, 0, 1],
point_on_axis=[0, 0, 0],
angle=pi / 3,
)
mesh = geom.generate_mesh()
OpenCASCADE
| <img src="https://nschloe.github.io/pygmsh/intersection.png" width="100%"> | <img src="https://nschloe.github.io/pygmsh/ellipsoid-holes.png" width="100%"> | <img src="https://nschloe.github.io/pygmsh/puzzle.png" width="100%"> | | :------------------------------------------------------------------------: | :---------------------------------------------------------------------------: | :------------------------------------------------------------------: | | | |
Gmsh also supports OpenCASCADE (occ), allowing for a CAD-style geometry specification.
from math import pi, cos
import pygmsh
with pygmsh.occ.Geometry() as geom:
geom.characteristic_length_max = 0.1
r = 0.5
disks = [
geom.add_disk([-0.5 * cos(7 / 6 * pi), -0.25], 1.0),
geom.add_disk([+0.5 * cos(7 / 6 * pi), -0.25], 1.0),
geom.add_disk([0.0, 0.5], 1.0),
]
geom.boolean_intersection(disks)
mesh = geom.generate_mesh()
# ellpsoid with holes
import pygmsh
with pygmsh.occ.Geometry() as geom:
geom.characteristic_length_max = 0.1
ellipsoid = geom.add_ellipsoid([0.0, 0.0, 0.0], [1.0, 0.7, 0.5])
cylinders = [
geom.add_cylinder([-1.0, 0.0, 0.0], [2.0, 0.0, 0.0], 0.3),
geom.add_cylinder([0.0, -1.0, 0.0], [0.0, 2.0, 0.0], 0.3),
geom.add_cylinder([0.0, 0.0, -1.0], [0.0, 0.0, 2.0], 0.3),
]
geom.boolean_difference(ellipsoid, geom.boolean_union(cylinders))
mesh = geom.generate_mesh()
# puzzle piece
import pygmsh
with pygmsh.occ.Geometry() as geom:
geom.characteristic_length_min = 0.1
geom.characteristic_length_max = 0.1
rectangle = geom.add_rectangle([-1.0, -1.0, 0.0], 2.0, 2.0)
disk1 = geom.add_disk([-1.2, 0.0, 0.0], 0.5)
disk2 = geom.add_disk([+1.2, 0.0, 0.0], 0.5)
disk3 = geom.add_disk([0.0, -0.9, 0.0], 0.5)
disk4 = geom.add_disk([0.0, +0.9, 0.0], 0.5)
flat = geom.boolean_difference(
geom.boolean_union([rectangle, disk1, disk2]),
geom.boolean_union([disk3, disk4]),
)
geom.extrude(flat, [0, 0, 0.3])
mesh = geom.generate_mesh()
Mesh refinement/boundary layers
| <img src="https://nschloe.github.io/pygmsh/boundary0.svg" width="100%"> | <img src="https://nschloe.github.io/pygmsh/mesh-refinement-2d.svg" width="100%"> | <img src="https://nschloe.github.io/pygmsh/ball-mesh-refinement.png" width="70%"> | | :---------------------------------------------------------------------: | :------------------------------------------------------------------------------: | :-------------------------------------------------------------------------------: | | | |
# boundary refinement
import pygmsh
with pygmsh.geo.Geometry() as geom:
poly = geom.add_polygon(
[
[0.0, 0.0],
[2.0, 0.0],
[3.0, 1.0],
[1.0, 2.0],
[0.0, 1.0],
],
mesh_size=0.3,
)
field0 = geom.add_boundary_layer(
edges_list=[poly.curves[0]],
lcmin=0.05,
lcmax=0.2,
distmin=0.0,
distmax=0.2,
)
field1 = geom.add_boundary_layer(
nodes_list=[poly.points[2]],
lcmin=0.05,
lcmax=0.2,
distmin=0.1,
distmax=0.4,
)
geom.set_background_mesh([field0, field1], operator="Min")
mesh = geom.generate_mesh()
