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

.. only:: html

    .. meta::
        :keywords: codex

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

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

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

.. _sphx_glr_gallery_specialty_plots_topographic_hillshading.py:


=======================
Topographic hillshading
=======================

Demonstrates the visual effect of varying blend mode and vertical exaggeration
on "hillshaded" plots.

Note that the "overlay" and "soft" blend modes work well for complex surfaces
such as this example, while the default "hsv" blend mode works best for smooth
surfaces such as many mathematical functions.

In most cases, hillshading is used purely for visual purposes, and *dx*/*dy*
can be safely ignored. In that case, you can tweak *vert_exag* (vertical
exaggeration) by trial and error to give the desired visual effect. However,
this example demonstrates how to use the *dx* and *dy* keyword arguments to
ensure that the *vert_exag* parameter is the true vertical exaggeration.

.. GENERATED FROM PYTHON SOURCE LINES 19-75



.. image-sg:: /gallery/specialty_plots/images/sphx_glr_topographic_hillshading_001.png
   :alt: 0.1, 1, 10
   :srcset: /gallery/specialty_plots/images/sphx_glr_topographic_hillshading_001.png, /gallery/specialty_plots/images/sphx_glr_topographic_hillshading_001_2_00x.png 2.00x
   :class: sphx-glr-single-img





.. code-block:: Python

    import matplotlib.pyplot as plt
    import numpy as np

    from matplotlib.cbook import get_sample_data
    from matplotlib.colors import LightSource

    dem = get_sample_data('jacksboro_fault_dem.npz')
    z = dem['elevation']
    # -- Optional dx and dy for accurate vertical exaggeration --------------------
    # If you need topographically accurate vertical exaggeration, or you don't want
    # to guess at what *vert_exag* should be, you'll need to specify the cellsize
    # of the grid (i.e. the *dx* and *dy* parameters).  Otherwise, any *vert_exag*
    # value you specify will be relative to the grid spacing of your input data
    # (in other words, *dx* and *dy* default to 1.0, and *vert_exag* is calculated
    # relative to those parameters).  Similarly, *dx* and *dy* are assumed to be in
    # the same units as your input z-values.  Therefore, we'll need to convert the
    # given dx and dy from decimal degrees to meters.
    dx, dy = dem['dx'], dem['dy']
    dy = 111200 * dy
    dx = 111200 * dx * np.cos(np.radians(dem['ymin']))
    # -----------------------------------------------------------------------------

    # Shade from the northwest, with the sun 45 degrees from horizontal
    ls = LightSource(azdeg=315, altdeg=45)
    cmap = plt.cm.gist_earth

    fig, axs = plt.subplots(nrows=4, ncols=3, figsize=(8, 9))
    plt.setp(axs.flat, xticks=[], yticks=[])

    # Vary vertical exaggeration and blend mode and plot all combinations
    for col, ve in zip(axs.T, [0.1, 1, 10]):
        # Show the hillshade intensity image in the first row
        col[0].imshow(ls.hillshade(z, vert_exag=ve, dx=dx, dy=dy), cmap='gray')

        # Place hillshaded plots with different blend modes in the rest of the rows
        for ax, mode in zip(col[1:], ['hsv', 'overlay', 'soft']):
            rgb = ls.shade(z, cmap=cmap, blend_mode=mode,
                           vert_exag=ve, dx=dx, dy=dy)
            ax.imshow(rgb)

    # Label rows and columns
    for ax, ve in zip(axs[0], [0.1, 1, 10]):
        ax.set_title(f'{ve}', size=18)
    for ax, mode in zip(axs[:, 0], ['Hillshade', 'hsv', 'overlay', 'soft']):
        ax.set_ylabel(mode, size=18)

    # Group labels...
    axs[0, 1].annotate('Vertical Exaggeration', (0.5, 1), xytext=(0, 30),
                       textcoords='offset points', xycoords='axes fraction',
                       ha='center', va='bottom', size=20)
    axs[2, 0].annotate('Blend Mode', (0, 0.5), xytext=(-30, 0),
                       textcoords='offset points', xycoords='axes fraction',
                       ha='right', va='center', size=20, rotation=90)
    fig.subplots_adjust(bottom=0.05, right=0.95)

    plt.show()


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

   **Total running time of the script:** (0 minutes 2.007 seconds)


.. _sphx_glr_download_gallery_specialty_plots_topographic_hillshading.py:

.. only:: html

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

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

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

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

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


.. only:: html

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

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