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pylab_examples example code: annotation_demo.pyΒΆ

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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

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',

# 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',

# 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),

# 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.annotate('the top',
            xy=(np.pi/2., 10.),      # theta, radius
            xytext=(np.pi/3, 20.),   # theta, radius
            arrowprops=dict(facecolor='black', shrink=0.05),
            clip_on=True)  # clip to the axes bounding box

ax.set_xlim([-20, 20])
ax.set_ylim([-20, 20])

Keywords: python, matplotlib, pylab, example, codex (see Search examples)