
.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "gallery/images_contours_and_fields/pcolormesh_levels.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_images_contours_and_fields_pcolormesh_levels.py>`
        to download the full example code.

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

.. _sphx_glr_gallery_images_contours_and_fields_pcolormesh_levels.py:


==========
pcolormesh
==========

`.axes.Axes.pcolormesh` allows you to generate 2D image-style plots.
Note that it is faster than the similar `~.axes.Axes.pcolor`.

.. GENERATED FROM PYTHON SOURCE LINES 10-17

.. code-block:: Python


    import matplotlib.pyplot as plt
    import numpy as np

    from matplotlib.colors import BoundaryNorm
    from matplotlib.ticker import MaxNLocator








.. GENERATED FROM PYTHON SOURCE LINES 18-24

Basic pcolormesh
----------------

We usually specify a pcolormesh by defining the edge of quadrilaterals and
the value of the quadrilateral.  Note that here *x* and *y* each have one
extra element than Z in the respective dimension.

.. GENERATED FROM PYTHON SOURCE LINES 24-33

.. code-block:: Python


    np.random.seed(19680801)
    Z = np.random.rand(6, 10)
    x = np.arange(-0.5, 10, 1)  # len = 11
    y = np.arange(4.5, 11, 1)  # len = 7

    fig, ax = plt.subplots()
    ax.pcolormesh(x, y, Z)




.. image-sg:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_001.png
   :alt: pcolormesh levels
   :srcset: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_001.png, /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_001_2_00x.png 2.00x
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 34-39

Non-rectilinear pcolormesh
--------------------------

Note that we can also specify matrices for *X* and *Y* and have
non-rectilinear quadrilaterals.

.. GENERATED FROM PYTHON SOURCE LINES 39-49

.. code-block:: Python


    x = np.arange(-0.5, 10, 1)  # len = 11
    y = np.arange(4.5, 11, 1)  # len = 7
    X, Y = np.meshgrid(x, y)
    X = X + 0.2 * Y  # tilt the coordinates.
    Y = Y + 0.3 * X

    fig, ax = plt.subplots()
    ax.pcolormesh(X, Y, Z)




.. image-sg:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_002.png
   :alt: pcolormesh levels
   :srcset: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_002.png, /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_002_2_00x.png 2.00x
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 50-59

Centered Coordinates
---------------------

Often a user wants to pass *X* and *Y* with the same sizes as *Z* to
`.axes.Axes.pcolormesh`. This is also allowed if ``shading='auto'`` is
passed (default set by :rc:`pcolor.shading`). Pre Matplotlib 3.3,
``shading='flat'`` would drop the last column and row of *Z*, but now gives
an error. If this is really what you want, then simply drop the last row and
column of Z manually:

.. GENERATED FROM PYTHON SOURCE LINES 59-71

.. code-block:: Python


    x = np.arange(10)  # len = 10
    y = np.arange(6)  # len = 6
    X, Y = np.meshgrid(x, y)

    fig, axs = plt.subplots(2, 1, sharex=True, sharey=True)
    axs[0].pcolormesh(X, Y, Z, vmin=np.min(Z), vmax=np.max(Z), shading='auto')
    axs[0].set_title("shading='auto' = 'nearest'")
    axs[1].pcolormesh(X, Y, Z[:-1, :-1], vmin=np.min(Z), vmax=np.max(Z),
                      shading='flat')
    axs[1].set_title("shading='flat'")




.. image-sg:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_003.png
   :alt: shading='auto' = 'nearest', shading='flat'
   :srcset: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_003.png, /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_003_2_00x.png 2.00x
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 72-79

Making levels using Norms
-------------------------

Shows how to combine Normalization and Colormap instances to draw
"levels" in `.axes.Axes.pcolor`, `.axes.Axes.pcolormesh`
and `.axes.Axes.imshow` type plots in a similar
way to the levels keyword argument to contour/contourf.

.. GENERATED FROM PYTHON SOURCE LINES 79-121

.. code-block:: Python


    # make these smaller to increase the resolution
    dx, dy = 0.05, 0.05

    # generate 2 2d grids for the x & y bounds
    y, x = np.mgrid[slice(1, 5 + dy, dy),
                    slice(1, 5 + dx, dx)]

    z = np.sin(x)**10 + np.cos(10 + y*x) * np.cos(x)

    # x and y are bounds, so z should be the value *inside* those bounds.
    # Therefore, remove the last value from the z array.
    z = z[:-1, :-1]
    levels = MaxNLocator(nbins=15).tick_values(z.min(), z.max())


    # pick the desired colormap, sensible levels, and define a normalization
    # instance which takes data values and translates those into levels.
    cmap = plt.colormaps['PiYG']
    norm = BoundaryNorm(levels, ncolors=cmap.N, clip=True)

    fig, (ax0, ax1) = plt.subplots(nrows=2)

    im = ax0.pcolormesh(x, y, z, cmap=cmap, norm=norm)
    fig.colorbar(im, ax=ax0)
    ax0.set_title('pcolormesh with levels')


    # contours are *point* based plots, so convert our bound into point
    # centers
    cf = ax1.contourf(x[:-1, :-1] + dx/2.,
                      y[:-1, :-1] + dy/2., z, levels=levels,
                      cmap=cmap)
    fig.colorbar(cf, ax=ax1)
    ax1.set_title('contourf with levels')

    # adjust spacing between subplots so `ax1` title and `ax0` tick labels
    # don't overlap
    fig.tight_layout()

    plt.show()




.. image-sg:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_004.png
   :alt: pcolormesh with levels, contourf with levels
   :srcset: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_004.png, /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_004_2_00x.png 2.00x
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 122-132

.. admonition:: References

   The use of the following functions, methods, classes and modules is shown
   in this example:

   - `matplotlib.axes.Axes.pcolormesh` / `matplotlib.pyplot.pcolormesh`
   - `matplotlib.axes.Axes.contourf` / `matplotlib.pyplot.contourf`
   - `matplotlib.figure.Figure.colorbar` / `matplotlib.pyplot.colorbar`
   - `matplotlib.colors.BoundaryNorm`
   - `matplotlib.ticker.MaxNLocator`


.. _sphx_glr_download_gallery_images_contours_and_fields_pcolormesh_levels.py:

.. only:: html

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

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

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

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

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

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

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


.. only:: html

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

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