PyVista -> TopoDS_Compound

Send a tessellated pyvista.PolyData back into the OCCT world as a faceted TopoDS_Compound. Useful when downstream OCCT-based code expects shape objects rather than meshes, e.g. boolean operations or further OCCT-native exports.

This example loads a real STEP part, the NIST AM Bench 2022 LPBF bridge specimen (public domain, https://doi.org/10.18434/mds2-2607), pushes it through to_topods, performs a boolean cut in OCCT (the kind of operation that only works on a TopoDS shape), then rounds it back to PyVista.

from OCP.BRepAlgoAPI import BRepAlgoAPI_Cut
from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
from OCP.gp import gp_Pnt
import pyvista as pv

import pyvista_cad
from pyvista_cad.examples import downloads

Load the real STEP part.

mesh = pyvista_cad.read_step(downloads.step_part_path()).combine().extract_surface()
mesh

/home/runner/work/pyvista-cad/pyvista-cad/examples/03_bridges/to_topods.py:30: 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.
  mesh = pyvista_cad.read_step(downloads.step_part_path()).combine().extract_surface()

PolyData (0x7f6fa8112aa0)
  N Cells:    436
  N Points:   690
  N Strips:   0
  X Bounds:   0.000e+00, 7.500e+01
  Y Bounds:   -2.446e-13, 5.000e+00
  Z Bounds:   0.000e+00, 1.225e+01
  N Arrays:   8

PolyData 690 points 436 cells 48 KiB

Bounds⧉X [0.000e+00, 7.500e+01]Y [-2.446e-13, 5.000e+00]Z [0.000e+00, 1.225e+01]

Cellsfaces 436

• Point Data: (1)
  • vtkOriginalPointIds⧉
    scalar
    int64
    [0.000e+00, 6.890e+02]
• Cell Data: (1)
  • vtkOriginalCellIds⧉
    scalar
    int64
    [0.000e+00, 4.350e+02]
• Field Data: (6)
  • cad.color⧉
    (4,)
    float64
  • cad.label⧉
    (1,)
    <U23
  • cad.source_format⧉
    (1,)
    <U4
  • cad.reader⧉
    (1,)
    <U21
  • cad.backend⧉
    (1,)
    <U9
  • cad.units⧉
    (1,)
    <U2

Push to OCCT.

shape = pyvista_cad.to_topods(mesh)
type(shape).__name__

'TopoDS_Shape'

Boolean-cut against an OCCT primitive: an operation that lives in TopoDS-land, not available on a PyVista mesh. The box trims one end of the specimen.

b = mesh.bounds
cutter = BRepPrimAPI_MakeBox(
    gp_Pnt(b.x_max - 10.0, b.y_min - 1.0, b.z_min - 1.0),
    20.0,
    (b.y_max - b.y_min) + 2.0,
    (b.z_max - b.z_min) + 2.0,
).Shape()
cut_result = BRepAlgoAPI_Cut(shape, cutter).Shape()
type(cut_result).__name__

'TopoDS_Shape'

Round-trip the cut compound back to PyVista.

back = pyvista_cad.from_topods(cut_result)
back

PolyData (0x7f6fa8110100)
  N Cells:    388
  N Points:   1152
  N Strips:   0
  X Bounds:   0.000e+00, 6.500e+01
  Y Bounds:   -2.446e-13, 5.000e+00
  Z Bounds:   0.000e+00, 1.225e+01
  N Arrays:   1

PolyData 1,152 points 388 cells 48 KiB

Bounds⧉X [0.000e+00, 6.500e+01]Y [-2.446e-13, 5.000e+00]Z [0.000e+00, 1.225e+01]

Cellsfaces 388

• Field Data: (1)
  • cad.source_format⧉
    (1,)
    <U3

Render the post-cut part.

back['X (mm)'] = back.points[:, 0]

pl = pv.Plotter()
pl.cad.add(back, scalars='X (mm)', cmap='inferno')
pl.show()

Static Scene

Interactive Scene