.. _images_contours_and_fields-pcolormesh_levels:

images_contours_and_fields example code: pcolormesh_levels.py
=============================================================



.. plot:: /build/matplotlib-ntJFVk/matplotlib-1.3.1/doc/mpl_examples/images_contours_and_fields/pcolormesh_levels.py

::

    """
    Shows how to combine Normalization and Colormap instances to draw
    "levels" in pcolor, pcolormesh and imshow type plots in a similar
    way to the levels keyword argument to contour/contourf.
    
    """
    
    import matplotlib.pyplot as plt
    from matplotlib.colors import BoundaryNorm
    from matplotlib.ticker import MaxNLocator
    import numpy as np
    
    
    # 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.get_cmap('PiYG')
    norm = BoundaryNorm(levels, ncolors=cmap.N, clip=True)
    
    plt.subplot(2, 1, 1)
    im = plt.pcolormesh(x, y, z, cmap=cmap, norm=norm)
    plt.colorbar()
    # set the limits of the plot to the limits of the data
    plt.axis([x.min(), x.max(), y.min(), y.max()])
    plt.title('pcolormesh with levels')
    
    
    
    plt.subplot(2, 1, 2)
    # contours are *point* based plots, so convert our bound into point
    # centers
    plt.contourf(x[:-1, :-1] + dx / 2.,
                 y[:-1, :-1] + dy / 2., z, levels=levels,
                 cmap=cmap)
    plt.colorbar()
    plt.title('contourf with levels')
    
    
    plt.show()

Keywords: python, matplotlib, pylab, example, codex (see :ref:`how-to-search-examples`)