Surface Smoothing

Smoothing rough edges of a surface mesh

import pyvista as pv
from pyvista import examples

Suppose you extract a volumetric subset of a dataset that has roughly defined edges. Perhaps you’d like a smooth representation of that model region. This can be achieved by extracting the bounding surface of the volume and applying a pyvista.PolyData.smooth() filter.

The below code snippet loads a sample roughly edged volumetric dataset:

# Vector to view rough edges
cpos = [-2, 5, 3]

# Load dataset
data = examples.load_uniform()
# Extract a rugged volume
vol = data.threshold_percent(30, invert=1)
vol.plot(show_edges=True, cpos=cpos, show_scalar_bar=False)

Extract the outer surface of the volume using the pyvista.DataSetFilters.extract_geometry() filter and then apply the smoothing filter:

# Get the out surface as PolyData
surf = vol.extract_geometry()
# Smooth the surface
smooth = surf.smooth()
smooth.plot(show_edges=True, cpos=cpos, show_scalar_bar=False)

Not smooth enough? Try increasing the number of iterations for the Laplacian smoothing algorithm:

# Smooth the surface even more
smooth = surf.smooth(n_iter=100)
smooth.plot(show_edges=True, cpos=cpos, show_scalar_bar=False)

Still not smooth enough? Increase the number of iterations for the Laplacian smoothing algorithm to a crazy high value. Note how this causes the mesh to “shrink”:

# Smooth the surface EVEN MORE
smooth = surf.smooth(n_iter=1000)

# extract the edges of the original unsmoothed mesh
orig_edges = surf.extract_feature_edges()

pl = pv.Plotter()
pl.add_mesh(smooth, show_edges=True, show_scalar_bar=False)
pl.camera_position = cpos
pl.add_mesh(orig_edges, show_scalar_bar=False, color='k', line_width=2)
pl.show()

Taubin Smoothing

You can reduce the amount of surface shrinkage by using Taubin smoothing rather than the default laplacian smoothing implemented in smooth(). In this example, you can see how Taubin smoothing maintains the volume relative to the original mesh.

Also, note that the number of iterations can be reduced to get the same approximate amount of smoothing. This is because Taubin smoothing is more efficient.

smooth_w_taubin = surf.smooth_taubin(n_iter=50, pass_band=0.05)

pl = pv.Plotter()
pl.add_mesh(smooth_w_taubin, show_edges=True, show_scalar_bar=False)
pl.camera_position = cpos
pl.add_mesh(orig_edges, show_scalar_bar=False, color='k', line_width=2)
pl.show()

# output the volumes of the original and smoothed meshes
print(f'Original surface volume:   {surf.volume:.1f}')
print(f'Laplacian smoothed volume: {smooth.volume:.1f}')
print(f'Taubin smoothed volume:    {smooth_w_taubin.volume:.1f}')

Out:

Original surface volume:   676.0
Laplacian smoothed volume: 468.3
Taubin smoothed volume:    680.0