Custom tessellation deflection

OCCT’s BRepMesh_IncrementalMesh exposes a linear and angular deflection knob. Coarser deflection yields fewer triangles; finer deflection yields smoother curves. read_step, read_brep, read_fcstd, and the build123d / cadquery bridges all forward these knobs.

The part is a real M3 nyloc lock nut from the FreeCAD parts library (CC-BY 3.0, FreeCAD-library contributors). Its helical thread and chamfers are exactly the curved features the deflection knob resolves, so the triangle count moves with the setting.

import pandas as pd
import pyvista as pv

import pyvista_cad
from pyvista_cad.examples import downloads

Tessellate the same real FCStd part at three deflection settings.

fcstd = downloads.fcstd_nut_path()
settings = [
    ('coarse', 0.5, 1.0),
    ('medium', 0.1, 0.5),
    ('fine', 0.02, 0.2),
]
meshes = {
    name: pyvista_cad.read_fcstd(fcstd, linear_deflection=lin, angular_deflection=ang)
    .combine()
    .extract_surface()
    for name, lin, ang in settings
}

pd.DataFrame(
    [
        {'setting': name, 'linear': lin, 'angular': ang, 'triangles': meshes[name].n_cells}
        for name, lin, ang in settings
    ]
)

/home/runner/work/pyvista-cad/pyvista-cad/examples/06_advanced/custom_tessellation.py:37: PyVistaFutureWarning: The default value of `algorithm` for the filter
`UnstructuredGrid.extract_surface` will change in the future. It currently defaults to
`'dataset_surface'`, but will change to `None`. Explicitly set the `algorithm` keyword to
silence this warning.
  .extract_surface()

	setting	linear	angular	triangles
0	coarse	0.50	1.0	4110
1	medium	0.10	0.5	8116
2	fine	0.02	0.2	29600

Side by side with the camera locked across views.

pl = pv.Plotter(shape=(1, 3))
for i, name in enumerate(['coarse', 'medium', 'fine']):
    pl.subplot(0, i)
    mesh = meshes[name]
    mesh['z'] = mesh.points[:, 2]
    pl.add_mesh(mesh, scalars='z', cmap='inferno', show_edges=True, edge_color='black')
pl.link_views()
pl.show()

Static Scene

Interactive Scene