Arc Identification

Meshwell can automatically identify sequences of vertices that form circular arcs. This reduces the complexity of the CAD model and improves mesh quality.

import matplotlib.pyplot as plt
import numpy as np
import shapely

from meshwell.cad_occ import cad_occ
from meshwell.mesh import mesh
from meshwell.occ_xao_writer import write_xao
from meshwell.polyline import PolyLine
from meshwell.polysurface import PolySurface

/home/runner/work/meshwell/meshwell/.venv/lib/python3.13/site-packages/tqdm/auto.py:21: TqdmWarning: IProgress not found. Please update jupyter and ipywidgets. See https://ipywidgets.readthedocs.io/en/stable/user_install.html
  from .autonotebook import tqdm as notebook_tqdm

# Create a circular geometry with many points
theta = np.linspace(0, np.pi / 2, 50)
vertices = [(np.cos(t), np.sin(t)) for t in theta]
vertices += [(0, 1), (0, 0), (1, 0)]
poly = shapely.Polygon(vertices)

PolySurface with Arc Identification

We enable identify_arcs=True to recover the true curved boundary.

ps = PolySurface(
    poly,
    identify_arcs=True,
    min_arc_points=4,
    arc_tolerance=1e-3,
    physical_name="curved_surface",
)

Visualize Decomposition

We can inspect how the polygon was partitioned into lines and arcs. Blue lines are straight segments, red lines are identified arcs.

ax = ps.plot_decomposition()
plt.show()

PolyLine with Arc Identification

# Create a wavy line that contains an arc
t = np.linspace(0, np.pi, 50)
arc_vertices = [(np.cos(t_val), np.sin(t_val)) for t_val in t]
line_vertices = [(1, 0), (2, 0), (2, 1)]
all_vertices = line_vertices + arc_vertices

pl = PolyLine(
    shapely.LineString(all_vertices), identify_arcs=True, physical_name="curved_wire"
)

ax = pl.plot_decomposition()
plt.show()

Meshing Results

Generate the mesh. Notice how the arcs are preserved in the underlying CAD.

write_xao(cad_occ([ps]), "arc_example.xao")
output_mesh = mesh(
    dim=2,
    input_file="arc_example.xao",
    output_file="arc_example.msh",
    default_characteristic_length=0.1,
    mesh_element_order=2,
)

Info    : Clearing all models and views...
Info    : Done clearing all models and views
Info    : Reading 'arc_example.xao'...
Info    : Done reading 'arc_example.xao'