.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "example_gallery/auto_examples/basic/extract_surface.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_example_gallery_auto_examples_basic_extract_surface.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_example_gallery_auto_examples_basic_extract_surface.py:


Extract a boundary surface from a volume mesh
=============================================

This tutorial extracts the boundary surface of a volume mesh and shows that the
surface points keep their connection to the parent volume points by default.

.. GENERATED FROM PYTHON SOURCE LINES 10-12

Imports
-------

.. GENERATED FROM PYTHON SOURCE LINES 12-18

.. code-block:: Python

    import numpy as np
    import pyvista as pv

    import graphlow









.. GENERATED FROM PYTHON SOURCE LINES 19-21

Step 1: Build a small volume mesh
---------------------------------

.. GENERATED FROM PYTHON SOURCE LINES 21-32

.. code-block:: Python

    def make_volume_grid() -> pv.UnstructuredGrid:
        """Create a small warped hexahedral grid."""
        x = np.array([0.0, 1.0, 2.2, 3.5], dtype=np.float32)
        y = np.array([0.0, 0.8, 1.7], dtype=np.float32)
        z = np.array([0.0, 0.6, 1.4], dtype=np.float32)
        X, Y, Z = np.meshgrid(x, y, z, indexing="ij")
        Z = Z + 0.12 * X * Y
        grid = pv.StructuredGrid(X, Y, Z)
        return grid.cast_to_unstructured_grid()









.. GENERATED FROM PYTHON SOURCE LINES 33-35

Step 2: Extract the surface
---------------------------

.. GENERATED FROM PYTHON SOURCE LINES 35-60

.. code-block:: Python

    def main() -> None:
        """Run the tutorial."""
        mesh = graphlow.from_pyvista(make_volume_grid(), backend="torch")
        mesh.requires_grad(True)

        surface = mesh.extract_surface()
        surface_area = surface.geometry.face_areas().sum()
        surface_area.backward()

        print(f"Volume mesh dimension: {mesh.topology.mesh_dim().name}")
        print(f"Surface mesh dimension: {surface.topology.mesh_dim().name}")
        print(f"Volume points / cells: {mesh.n_points} / {mesh.n_cells}")
        print(f"Surface points / cells: {surface.n_points} / {surface.n_cells}")
        print(f"Gradient reached the volume points: {mesh.points.grad is not None}")

        plotter = pv.Plotter(window_size=[800, 600])
        plotter.add_mesh(mesh.pvmesh, style="wireframe", color="gray", opacity=0.3)
        plotter.add_mesh(surface.pvmesh, show_edges=True, color="tomato")
        plotter.show_bounds(mesh=mesh.pvmesh, location="outer")
        plotter.camera_position = "iso"
        plotter.show()


    if __name__ == "__main__":
        main()



.. image-sg:: /example_gallery/auto_examples/basic/images/sphx_glr_extract_surface_001.png
   :alt: extract surface
   :srcset: /example_gallery/auto_examples/basic/images/sphx_glr_extract_surface_001.png
   :class: sphx-glr-single-img


.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    Volume mesh dimension: VOLUME
    Surface mesh dimension: SURFACE
    Volume points / cells: 36 / 12
    Surface points / cells: 34 / 32
    Gradient reached the volume points: True





.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 0.243 seconds)


.. _sphx_glr_download_example_gallery_auto_examples_basic_extract_surface.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: extract_surface.ipynb <extract_surface.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: extract_surface.py <extract_surface.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: extract_surface.zip <extract_surface.zip>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_