.. only:: html .. note:: :class: sphx-glr-download-link-note Click :ref:`here ` to download the full example code .. rst-class:: sphx-glr-example-title .. _sphx_glr_gallery_images_contours_and_fields_pcolormesh_grids.py: ============================ pcolormesh grids and shading ============================ `.axes.Axes.pcolormesh` and `~.axes.Axes.pcolor` have a few options for how grids are laid out and the shading between the grid points. Generally, if *Z* has shape *(M, N)* then the grid *X* and *Y* can be specified with either shape *(M+1, N+1)* or *(M, N)*, depending on the argument for the ``shading`` keyword argument. Note that below we specify vectors *x* as either length N or N+1 and *y* as length M or M+1, and `~.axes.Axes.pcolormesh` internally makes the mesh matrices *X* and *Y* from the input vectors. .. code-block:: default import matplotlib import matplotlib.pyplot as plt import numpy as np Flat Shading ------------ The grid specification with the least assumptions is ``shading='flat'`` and if the grid is one larger than the data in each dimension, i.e. has shape *(M+1, N+1)*. In that case *X* and *Y* specify the corners of quadrilaterals that are colored with the values in *Z*. Here we specify the edges of the *(3, 5)* quadrilaterals with *X* and *Y* that are *(4, 6)*. .. code-block:: default nrows = 3 ncols = 5 Z = np.arange(nrows * ncols).reshape(nrows, ncols) x = np.arange(ncols + 1) y = np.arange(nrows + 1) fig, ax = plt.subplots() ax.pcolormesh(x, y, Z, shading='flat', vmin=Z.min(), vmax=Z.max()) def _annotate(ax, x, y, title): # this all gets repeated below: X, Y = np.meshgrid(x, y) ax.plot(X.flat, Y.flat, 'o', color='m') ax.set_xlim(-0.7, 5.2) ax.set_ylim(-0.7, 3.2) ax.set_title(title) _annotate(ax, x, y, "shading='flat'") .. image:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_grids_001.png :alt: shading='flat' :class: sphx-glr-single-img Flat Shading, same shape grid ----------------------------- Often, however, data is provided where *X* and *Y* match the shape of *Z*. As of Matplotlib v3.3, ``shading='flat'`` is deprecated when this is the case, a warning is raised, and the last row and column of *Z* are dropped. This dropping of the last row and column is what Matplotlib did silently previous to v3.3, and is compatible with what Matlab does. .. code-block:: default x = np.arange(ncols) # note *not* ncols + 1 as before y = np.arange(nrows) fig, ax = plt.subplots() ax.pcolormesh(x, y, Z, shading='flat', vmin=Z.min(), vmax=Z.max()) _annotate(ax, x, y, "shading='flat': X, Y, C same shape") .. image:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_grids_002.png :alt: shading='flat': X, Y, C same shape :class: sphx-glr-single-img .. rst-class:: sphx-glr-script-out Out: .. code-block:: none /root/matplotlib/examples/images_contours_and_fields/pcolormesh_grids.py:66: MatplotlibDeprecationWarning: shading='flat' when X and Y have the same dimensions as C is deprecated since 3.3. Either specify the corners of the quadrilaterals with X and Y, or pass shading='auto', 'nearest' or 'gouraud', or set rcParams['pcolor.shading']. This will become an error two minor releases later. ax.pcolormesh(x, y, Z, shading='flat', vmin=Z.min(), vmax=Z.max()) Nearest Shading, same shape grid -------------------------------- Usually, dropping a row and column of data is not what the user means when they make *X*, *Y* and *Z* all the same shape. For this case, Matplotlib allows ``shading='nearest'`` and centers the colored quadrilaterals on the grid points. If a grid that is not the correct shape is passed with ``shading='nearest'`` an error is raised. .. code-block:: default fig, ax = plt.subplots() ax.pcolormesh(x, y, Z, shading='nearest', vmin=Z.min(), vmax=Z.max()) _annotate(ax, x, y, "shading='nearest'") .. image:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_grids_003.png :alt: shading='nearest' :class: sphx-glr-single-img Auto Shading ------------ It's possible that the user would like the code to automatically choose which to use, in this case ``shading='auto'`` will decide whether to use 'flat' or 'nearest' shading based on the shapes of *X*, *Y* and *Z*. .. code-block:: default fig, axs = plt.subplots(2, 1, constrained_layout=True) ax = axs x = np.arange(ncols) y = np.arange(nrows) ax.pcolormesh(x, y, Z, shading='auto', vmin=Z.min(), vmax=Z.max()) _annotate(ax, x, y, "shading='auto'; X, Y, Z: same shape (nearest)") ax = axs x = np.arange(ncols + 1) y = np.arange(nrows + 1) ax.pcolormesh(x, y, Z, shading='auto', vmin=Z.min(), vmax=Z.max()) _annotate(ax, x, y, "shading='auto'; X, Y one larger than Z (flat)") .. image:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_grids_004.png :alt: shading='auto'; X, Y, Z: same shape (nearest), shading='auto'; X, Y one larger than Z (flat) :class: sphx-glr-single-img Gouraud Shading --------------- `Gouraud shading `_ can also be specified, where the color in the quadrilaterals is linearly interpolated between the grid points. The shapes of *X*, *Y*, *Z* must be the same. .. code-block:: default fig, ax = plt.subplots(constrained_layout=True) x = np.arange(ncols) y = np.arange(nrows) ax.pcolormesh(x, y, Z, shading='gouraud', vmin=Z.min(), vmax=Z.max()) _annotate(ax, x, y, "shading='gouraud'; X, Y same shape as Z") plt.show() .. image:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_grids_005.png :alt: shading='gouraud'; X, Y same shape as Z :class: sphx-glr-single-img ------------ References """""""""" The use of the following functions and methods is shown in this example: .. code-block:: default matplotlib.axes.Axes.pcolormesh matplotlib.pyplot.pcolormesh .. rst-class:: sphx-glr-script-out Out: .. code-block:: none .. rst-class:: sphx-glr-timing **Total running time of the script:** ( 0 minutes 1.855 seconds) .. _sphx_glr_download_gallery_images_contours_and_fields_pcolormesh_grids.py: .. only :: html .. container:: sphx-glr-footer :class: sphx-glr-footer-example .. container:: sphx-glr-download sphx-glr-download-python :download:`Download Python source code: pcolormesh_grids.py ` .. container:: sphx-glr-download sphx-glr-download-jupyter :download:`Download Jupyter notebook: pcolormesh_grids.ipynb ` .. only:: html .. rst-class:: sphx-glr-signature Keywords: matplotlib code example, codex, python plot, pyplot `Gallery generated by Sphinx-Gallery `_