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87 lines
3.8 KiB
ReStructuredText
Executable file
.. _annotations-tutorial:
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Annotating text
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===============
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For a more detailed introduction to annotations, see
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:ref:`plotting-guide-annotation`.
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The uses of the basic :func:`~matplotlib.pyplot.text` command above
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place text at an arbitrary position on the Axes. A common use case of
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text is to annotate some feature of the plot, and the
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:func:`~matplotlib.Axes.annotate` method provides helper functionality
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to make annotations easy. In an annotation, there are two points to
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consider: the location being annotated represented by the argument
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``xy`` and the location of the text ``xytext``. Both of these
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arguments are ``(x,y)`` tuples.
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.. plot:: pyplots/annotation_basic.py
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:include-source:
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In this example, both the ``xy`` (arrow tip) and ``xytext`` locations
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(text location) are in data coordinates. There are a variety of other
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coordinate systems one can choose -- you can specify the coordinate
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system of ``xy`` and ``xytext`` with one of the following strings for
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``xycoords`` and ``textcoords`` (default is 'data')
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==================== ====================================================
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argument coordinate system
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==================== ====================================================
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'figure points' points from the lower left corner of the figure
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'figure pixels' pixels from the lower left corner of the figure
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'figure fraction' 0,0 is lower left of figure and 1,1 is upper, right
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'axes points' points from lower left corner of axes
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'axes pixels' pixels from lower left corner of axes
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'axes fraction' 0,1 is lower left of axes and 1,1 is upper right
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'data' use the axes data coordinate system
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==================== ====================================================
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For example to place the text coordinates in fractional axes
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coordinates, one could do::
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ax.annotate('local max', xy=(3, 1), xycoords='data',
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xytext=(0.8, 0.95), textcoords='axes fraction',
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arrowprops=dict(facecolor='black', shrink=0.05),
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horizontalalignment='right', verticalalignment='top',
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)
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For physical coordinate systems (points or pixels) the origin is the
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(bottom, left) of the figure or axes. If the value is negative,
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however, the origin is from the (right, top) of the figure or axes,
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analogous to negative indexing of sequences.
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Optionally, you can specify arrow properties which draws an arrow
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from the text to the annotated point by giving a dictionary of arrow
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properties in the optional keyword argument ``arrowprops``.
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==================== =====================================================
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``arrowprops`` key description
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==================== =====================================================
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width the width of the arrow in points
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frac the fraction of the arrow length occupied by the head
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headwidth the width of the base of the arrow head in points
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shrink move the tip and base some percent away from
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the annotated point and text
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\*\*kwargs any key for :class:`matplotlib.patches.Polygon`,
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e.g. ``facecolor``
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==================== =====================================================
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In the example below, the ``xy`` point is in native coordinates
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(``xycoords`` defaults to 'data'). For a polar axes, this is in
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(theta, radius) space. The text in this example is placed in the
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fractional figure coordinate system. :class:`matplotlib.text.Text`
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keyword args like ``horizontalalignment``, ``verticalalignment`` and
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``fontsize are passed from the `~matplotlib.Axes.annotate` to the
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``Text`` instance
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.. plot:: pyplots/annotation_polar.py
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:include-source:
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For more on all the wild and wonderful things you can do with
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annotations, including fancy arrows, see :ref:`plotting-guide-annotation`
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and :ref:`pylab_examples-annotation_demo`.
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