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"""
.. _decimate_example:
Decimation
~~~~~~~~~~
Decimate a mesh
"""
# sphinx_gallery_thumbnail_number = 4
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)
# %%
# Now let's define a target reduction and compare the
# :func:`pyvista.PolyDataFilters.decimate` and
# :func:`pyvista.PolyDataFilters.decimate_pro` filters.
target_reduction = 0.7
print(f'Reducing {target_reduction * 100.0} percent out of the original mesh')
# %%
decimated = mesh.decimate(target_reduction)
decimated.plot(cpos=cpos, **dargs)
# %%
pro_decimated = mesh.decimate_pro(target_reduction, preserve_topology=True)
pro_decimated.plot(cpos=cpos, **dargs)
# %%
# Side by side comparison:
# sphinx_gallery_start_ignore
# text missing in interactive
PYVISTA_GALLERY_FORCE_STATIC = True
# sphinx_gallery_end_ignore
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 :func:`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}')
# %%
# 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}')
# %%
# 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}')
# %%
# The structure of the inner part of the spiral is captured adequately.
compare_decimation(spiral, decimated)
# %%
# .. tags:: filter
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