"""
.. _extract_edges_example:

Extract Edges
~~~~~~~~~~~~~

Extract edges from a surface.
"""

# sphinx_gallery_thumbnail_number = 2
import pyvista as pv
from pyvista import examples

# %%
# From vtk documentation, the edges of a mesh are one of the following:
#
# 1. boundary (used by one polygon) or a line cell
# 2. non-manifold (used by three or more polygons)
# 3. feature edges (edges used by two triangles and whose dihedral angle > feature_angle)
# 4. manifold edges (edges used by exactly two polygons).
#
# The :func:`extract_feature_edges() <pyvista.DataSetFilters.extract_feature_edges>`
# filter will extract those edges given a feature angle and return a dataset
# with lines that represent the edges of the original mesh.
#
# To demonstrate, we will first extract the edges around a sample CAD model:

# Download the example CAD model and extract all feature edges above 45 degrees
mesh = examples.download_cad_model()
edges = mesh.extract_feature_edges(45)

# Render the edge lines on top of the original mesh.  Zoom in to provide a better figure.
pl = pv.Plotter()
pl.add_mesh(mesh, color=True)
pl.add_mesh(edges, color='red', line_width=5)
pl.camera.zoom(1.5)
pl.show()


# %%
# We can do this analysis for any :class:`pyvista.PolyData` object. Let's try
# the cow mesh example:

mesh = examples.download_cow()
edges = mesh.extract_feature_edges(20)

pl = pv.Plotter()
pl.add_mesh(mesh, color=True)
pl.add_mesh(edges, color='red', line_width=5)
pl.camera_position = pv.CameraPosition(
    position=(9.5, 3.0, 5.5), focal_point=(2.5, 1, 0), viewup=(0, 1, 0)
)
pl.show()


# %%
# We can leverage the :any:`pyvista.PolyData.n_open_edges` property and
# :func:`pyvista.DataSetFilters.extract_feature_edges` filter to count and
# extract the open edges on a :class:`pyvista.PolyData` mesh.

# Download a sample surface mesh with visible open edges
mesh = examples.download_bunny()
mesh

# %%
# We can get a count of the open edges with:
mesh.n_open_edges


# %%
# And we can extract those edges with the ``boundary_edges`` option of
# :func:`pyvista.DataSetFilters.extract_feature_edges`:
edges = mesh.extract_feature_edges(
    boundary_edges=True, feature_edges=False, manifold_edges=False
)

pl = pv.Plotter()
pl.add_mesh(mesh, color=True)
pl.add_mesh(edges, color='red', line_width=5)
pl.camera_position = pv.CameraPosition(
    position=(-0.2, -0.13, 0.12),
    focal_point=(-0.015, 0.10, -0.0),
    viewup=(0.28, 0.26, 0.9),
)
pl.show()
# %%
# .. tags:: filter
