Visualization

gmshparser itself has no plotting dependency. The helper functions in gmshparser.helpers prepare 2D mesh data for optional matplotlib use and accept both modern read() meshes and compatibility parse() meshes.

Install matplotlib:

uv add matplotlib

For a repository checkout:

uv sync --group visualization

Triangular meshes

get_triangles() returns (X, Y, T), where T contains zero-based indices into X and Y:

import gmshparser
import matplotlib.pyplot as plt

mesh = gmshparser.read("mesh.msh")
X, Y, triangles = gmshparser.helpers.get_triangles(mesh)

plt.triplot(X, Y, triangles, color="black", linewidth=0.5)
plt.axis("equal")
plt.show()

Only three-node triangular elements are included.

Quadrilateral meshes

get_quads() also returns zero-based connectivity:

import gmshparser
import matplotlib.pyplot as plt
from matplotlib.patches import Polygon

mesh = gmshparser.read("quad_mesh.msh")
X, Y, quads = gmshparser.helpers.get_quads(mesh)

figure, axes = plt.subplots()
for quad in quads:
    coordinates = [(X[index], Y[index]) for index in quad]
    axes.add_patch(Polygon(coordinates, fill=False, edgecolor="black"))

axes.autoscale_view()
axes.set_aspect("equal")
plt.show()

Only four-node quadrilateral elements are included.

Mixed triangle and quadrilateral meshes

get_elements_2d() returns a dictionary and retains original Gmsh node tags in the connectivity lists.

import gmshparser
import matplotlib.pyplot as plt
from matplotlib.patches import Polygon

mesh = gmshparser.read("mixed_mesh.msh")
data = gmshparser.helpers.get_elements_2d(mesh)

nodes = data["nodes"]
triangles = data["triangles"]
quads = data["quads"]

figure, axes = plt.subplots()

for triangle in triangles:
    coordinates = [nodes[node_tag] for node_tag in triangle]
    axes.add_patch(Polygon(coordinates, fill=False, edgecolor="black"))

for quad in quads:
    coordinates = [nodes[node_tag] for node_tag in quad]
    axes.add_patch(Polygon(coordinates, fill=False, edgecolor="black"))

axes.autoscale_view()
axes.set_aspect("equal")
plt.show()

Node and element labels

The triangle helper connectivity refers to positions in X and Y, not to original Gmsh node tags. Label the plotted positions accordingly:

for index, (x, y) in enumerate(zip(X, Y, strict=True)):
    axes.text(x, y, str(index))

To preserve original node tags, use get_elements_2d() and its nodes dictionary instead.

Filtering before plotting

The modern API can select elements before custom plotting:

from gmshparser.api import ElementType

surface_triangles = mesh.elements.where(
    element_type=ElementType.TRIANGLE,
    dimension=2,
)
for triangle in surface_triangles:
    coordinates = [node.coordinates[:2] for node in triangle]

The convenience helpers currently operate on the complete mesh. Direct collection filtering is useful when plotting only selected entities.

Large meshes

All helpers construct Python lists and load their result in memory. For dense meshes, plotting every edge may be slow and visually unhelpful. Consider plotting only selected entities or a subset of elements.

API reference

See Helpers API for the exact return values of each helper.