Decimation

Decimate a mesh

from __future__ import annotations

import numpy as np

import pyvista as pv
from pyvista import examples

mesh = examples.download_face()

# Define a camera position that shows this mesh properly
cpos = [(0.4, -0.07, -0.31), (0.05, -0.13, -0.06), (-0.1, 1, 0.08)]
dargs = dict(show_edges=True, color=True)

# Preview the mesh
mesh.plot(cpos=cpos, **dargs)

Static Scene

Interactive Scene

Now let’s define a target reduction and compare the pyvista.PolyDataFilters.decimate() and pyvista.PolyDataFilters.decimate_pro() filters.

target_reduction = 0.7
print(f'Reducing {target_reduction * 100.0} percent out of the original mesh')

Reducing 70.0 percent out of the original mesh

decimated = mesh.decimate(target_reduction)

decimated.plot(cpos=cpos, **dargs)

Static Scene

Interactive Scene

pro_decimated = mesh.decimate_pro(target_reduction, preserve_topology=True)

pro_decimated.plot(cpos=cpos, **dargs)

Static Scene

Interactive Scene

Side by side comparison:

pl = pv.Plotter(shape=(1, 3))
pl.add_mesh(mesh, **dargs)
pl.add_text('Input mesh', font_size=24)
pl.camera_position = cpos
pl.reset_camera()
pl.subplot(0, 1)
pl.add_mesh(decimated, **dargs)
pl.add_text('Decimated mesh', font_size=24)
pl.camera_position = cpos
pl.reset_camera()
pl.subplot(0, 2)
pl.add_mesh(pro_decimated, **dargs)
pl.add_text('Pro Decimated mesh', font_size=24)
pl.camera_position = cpos
pl.reset_camera()
pl.link_views()
pl.show()

Decimate Polyline Mesh

Generate a fairly slow spiral polyline mesh.

n_points = 100
n_rotations = 5
phi = np.linspace(0, 2 * np.pi * n_rotations, n_points)
ratio = 1.1
r = ratio ** (phi)

points = np.zeros((n_points, 3))
points[:, 0] = r * np.cos(phi)
points[:, 1] = r * np.sin(phi)

spiral = pv.PolyData(points, lines=np.append([n_points], np.arange(n_points)))

Construct a reusable plotting function for future use.

def compare_decimation(spiral, decimated):
    pl = pv.Plotter()
    pl.add_mesh(spiral, line_width=5, color='r', label='Original')
    pl.add_mesh(decimated, line_width=3, color='k', label='Decimated')
    pl.view_xy()
    pl.add_legend(face='line', size=(0.25, 0.25))

Decimate using pyvista.PolyDataFilters.decimate_polyline() filter by target of 50%.

decimated = spiral.decimate_polyline(0.5)
print(f'Original # of points:  {spiral.n_points}')
print(f'Decimated # of points: {decimated.n_points}')

Original # of points:  100
Decimated # of points: 50

The decimation looks OK at this level of reduction.

compare_decimation(spiral, decimated)

Using a larger level of reduction, 80%, leads to a much coarser level of representation.

decimated = spiral.decimate_polyline(0.8)
print(f'Original # of points:  {spiral.n_points}')
print(f'Decimated # of points: {decimated.n_points}')

Original # of points:  100
Decimated # of points: 20

The structure of the inner part of the spiral is completely lost.

compare_decimation(spiral, decimated)

To avoid errors of quickly changing features, use the maximum_error parameter. It is in units of fraction of the largest length of the bounding box. Note that it limits the level of reduction achieved.

decimated = spiral.decimate_polyline(0.8, maximum_error=0.5)
print(f'Original # of points:  {spiral.n_points}')
print(f'Decimated # of points: {decimated.n_points}')

Original # of points:  100
Decimated # of points: 45

The structure of the inner part of the spiral is captured adequately.

compare_decimation(spiral, decimated)

Tags: filter