# Decimation
# ==========

# Decimate a mesh
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 = pv.CameraPosition(
    position=(0.4, -0.07, -0.31), focal_point=(0.05, -0.13, -0.06), viewup=(-0.1, 1, 0.08)
)
plot_kwargs = dict(show_edges=True, color=True)

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

# 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')

decimated = mesh.decimate(target_reduction)

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

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

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

# Side by side comparison:
datasets = {
    'Input': mesh,
    'Decimated': decimated,
    'Pro Decimated': pro_decimated,
}

pv.plot_compare(
    datasets,
    label_size=24,
    cpos=cpos,
    **plot_kwargs,
)

# 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}')

# 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)

# ----------------------------------------------------------------------
# Generated by sphinx-examples-as-code https://github.com/pyvista/sphinx-examples-as-code