Clip and Cap a Closed Surface

Compare a standard planar clip, which leaves an open boundary, with pyvista.PolyDataFilters.clip_closed_surface(), which seals the cut face.

import pyvista as pv
from pyvista import examples

Load a closed surface

The download_lucy() scan is a watertight, manifold PolyData surface with no open edges.

surface = examples.download_lucy().triangulate()
surface

PolyData (0x71196a436800)
  N Cells:    99970
  N Points:   49987
  N Strips:   0
  X Bounds:   2.259e+02, 1.156e+03
  Y Bounds:   -3.884e+02, 1.453e+02
  Z Bounds:   -6.059e+02, 9.913e+02
  N Arrays:   0

PolyData 49,987 points 99,970 cells 3.6 MiB

Bounds⧉X [2.259e+02, 1.156e+03]Y [-3.884e+02, 1.453e+02]Z [-6.059e+02, 9.913e+02]

Cellsfaces 99,970

Define an oblique cutting plane

The same plane is reused for both the open and the closed-surface clip.

plane_origin = surface.center
plane_normal = (1, 0.3, 0)
plane_size = surface.length * 1.2
plane = pv.Plane(
    center=plane_origin, direction=plane_normal, i_size=plane_size, j_size=plane_size
)

pl = pv.Plotter()
pl.add_mesh(surface, color='wheat', smooth_shading=True)
pl.add_mesh(plane, style='wireframe', color='black', line_width=2)
pl.view_xz()
pl.camera.azimuth = 35
pl.show()

Static Scene

Interactive Scene

Compare an open cut to a capped cut

A standard clip leaves a boundary loop along the cut. The closed-surface clip caps that loop with new triangles and stays watertight.

open_clip = surface.clip(normal=plane_normal, origin=plane_origin)
closed_clip = surface.clip_closed_surface(normal=plane_normal, origin=plane_origin)

open_boundary = open_clip.extract_feature_edges(
    boundary_edges=True,
    feature_edges=False,
    manifold_edges=False,
    non_manifold_edges=False,
)

pl = pv.Plotter(shape=(1, 2))
pl.subplot(0, 0)
pl.add_mesh(open_clip, color='wheat', smooth_shading=True)
pl.add_mesh(open_boundary, color='tomato', line_width=6)
pl.add_mesh(plane, style='wireframe', color='black', line_width=2)
pl.view_xz()
pl.camera.azimuth = 35
pl.subplot(0, 1)
pl.add_mesh(closed_clip, color='wheat', smooth_shading=True)
pl.add_mesh(plane, style='wireframe', color='black', line_width=2)
pl.view_xz()
pl.camera.azimuth = 35
pl.link_views()
pl.show()

Static Scene

Interactive Scene

Confirm that the capped result is watertight

The open clip carries hundreds of boundary edges; the capped result has none.

open_boundary.n_cells, closed_clip.n_open_edges

(1082, 0)

Tags: filter