.. _pylab_examples-annotation_demo:

pylab_examples example code: annotation_demo.py
===============================================



.. plot:: /home/tcaswell/source/p/matplotlib/doc/mpl_examples/pylab_examples/annotation_demo.py

::

    """
    Some examples of how to annotate points in figures.  You specify an
    annotation point xy=(x,y) and a text point xytext=(x,y) for the
    annotated points and text location, respectively.  Optionally, you can
    specify the coordinate system of xy and xytext with one of the
    following strings for xycoords and textcoords (default is 'data')
    
    
      'figure points'   : points from the lower left corner of the figure
      'figure pixels'   : pixels from the lower left corner of the figure
      'figure fraction' : 0,0 is lower left of figure and 1,1 is upper, right
      'axes points'     : points from lower left corner of axes
      'axes pixels'     : pixels from lower left corner of axes
      'axes fraction'   : 0,0 is lower left of axes and 1,1 is upper right
      'offset points'   : Specify an offset (in points) from the xy value
      'offset pixels'   : Specify an offset (in pixels) from the xy value
      'data'            : use the axes data coordinate system
    
    Optionally, you can specify arrow properties which draws and arrow
    from the text to the annotated point by giving a dictionary of arrow
    properties
    
    Valid keys are
    
              width : the width of the arrow in points
              frac  : the fraction of the arrow length occupied by the head
              headwidth : the width of the base of the arrow head in points
              shrink : move the tip and base some percent away from the
                       annotated point and text
              any key for matplotlib.patches.polygon  (e.g., facecolor)
    
    For physical coordinate systems (points or pixels) the origin is the
    (bottom, left) of the figure or axes.
    """
    
    
    import matplotlib.pyplot as plt
    from matplotlib.patches import Ellipse
    import numpy as np
    
    
    # If only one location is given, the text and xypoint being
    # annotated are assumed to be the same
    fig = plt.figure()
    ax = fig.add_subplot(111, autoscale_on=False, xlim=(-1, 5), ylim=(-3, 5))
    
    t = np.arange(0.0, 5.0, 0.01)
    s = np.cos(2*np.pi*t)
    line, = ax.plot(t, s)
    
    ax.annotate('figure pixels',
                xy=(10, 10), xycoords='figure pixels')
    
    ax.annotate('figure points',
                xy=(80, 80), xycoords='figure points')
    
    ax.annotate('point offset from data',
                xy=(2, 1), xycoords='data',
                xytext=(-15, 25), textcoords='offset points',
                arrowprops=dict(facecolor='black', shrink=0.05),
                horizontalalignment='right', verticalalignment='bottom')
    
    ax.annotate('axes fraction',
                xy=(3, 1), xycoords='data',
                xytext=(0.8, 0.95), textcoords='axes fraction',
                arrowprops=dict(facecolor='black', shrink=0.05),
                horizontalalignment='right', verticalalignment='top')
    
    ax.annotate('figure fraction',
                xy=(.025, .975), xycoords='figure fraction',
                horizontalalignment='left', verticalalignment='top',
                fontsize=20)
    
    # use negative points or pixels to specify from right, top -10, 10
    # is 10 points to the left of the right side of the axes and 10
    # points above the bottom
    ax.annotate('pixel offset from axes fraction',
                xy=(1, 0), xycoords='axes fraction',
                xytext=(-20, 20), textcoords='offset pixels',
                horizontalalignment='right',
                verticalalignment='bottom')
    
    
    # You can specify the xypoint and the xytext in different positions and
    # coordinate systems, and optionally turn on a connecting line and mark
    # the point with a marker.  Annotations work on polar axes too.
    # In the example below, the xy point is in native coordinates (xycoords
    # defaults to 'data').  For a polar axes, this is in (theta, radius) space.
    # The text in the example is placed in the fractional figure coordinate system.
    # Text keyword args like horizontal and vertical alignment are respected.
    fig = plt.figure()
    ax = fig.add_subplot(111, projection='polar')
    r = np.arange(0, 1, 0.001)
    theta = 2*2*np.pi*r
    line, = ax.plot(theta, r)
    
    ind = 800
    thisr, thistheta = r[ind], theta[ind]
    ax.plot([thistheta], [thisr], 'o')
    ax.annotate('a polar annotation',
                xy=(thistheta, thisr),  # theta, radius
                xytext=(0.05, 0.05),    # fraction, fraction
                textcoords='figure fraction',
                arrowprops=dict(facecolor='black', shrink=0.05),
                horizontalalignment='left',
                verticalalignment='bottom')
    
    
    # You can also use polar notation on a cartesian axes.  Here the native
    # coordinate system ('data') is cartesian, so you need to specify the
    # xycoords and textcoords as 'polar' if you want to use (theta, radius).
    
    el = Ellipse((0, 0), 10, 20, facecolor='r', alpha=0.5)
    
    fig = plt.figure()
    ax = fig.add_subplot(111, aspect='equal')
    ax.add_artist(el)
    el.set_clip_box(ax.bbox)
    ax.annotate('the top',
                xy=(np.pi/2., 10.),      # theta, radius
                xytext=(np.pi/3, 20.),   # theta, radius
                xycoords='polar',
                textcoords='polar',
                arrowprops=dict(facecolor='black', shrink=0.05),
                horizontalalignment='left',
                verticalalignment='bottom',
                clip_on=True)  # clip to the axes bounding box
    
    ax.set_xlim([-20, 20])
    ax.set_ylim([-20, 20])
    
    plt.show()
    

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