matplotlib/tutorials/text/annotations.py at v3.3.x · matplotlib/matplotlib · GitHub

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r"""

Annotations

===========

Annotating text with Matplotlib.

.. contents:: Table of Contents

:depth: 3

.. _annotations-tutorial:

Basic annotation

----------------

The uses of the basic :func:`~matplotlib.pyplot.text` will place text

at an arbitrary position on the Axes. A common use case of text is to

annotate some feature of the plot, and the

:func:`~matplotlib.axes.Axes.annotate` method provides helper functionality

to make annotations easy. In an annotation, there are two points to

consider: the location being annotated represented by the argument

*xy* and the location of the text *xytext*. Both of these

arguments are ``(x, y)`` tuples.

.. figure:: ../../gallery/pyplots/images/sphx_glr_annotation_basic_001.png

:target: ../../gallery/pyplots/annotation_basic.html

:align: center

:scale: 50

Annotation Basic

In this example, both the *xy* (arrow tip) and *xytext* locations

(text location) are in data coordinates. There are a variety of other

coordinate systems one can choose -- you can specify the coordinate

system of *xy* and *xytext* with one of the following strings for

*xycoords* and *textcoords* (default is 'data')

================== ========================================================

argument coordinate system

================== ========================================================

'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

'data' use the axes data coordinate system

================== ========================================================

For example to place the text coordinates in fractional axes

coordinates, one could do::

ax.annotate('local max', xy=(3, 1), xycoords='data',

xytext=(0.8, 0.95), textcoords='axes fraction',

arrowprops=dict(facecolor='black', shrink=0.05),

horizontalalignment='right', verticalalignment='top',

)

For physical coordinate systems (points or pixels) the origin is the

bottom-left of the figure or axes.

Optionally, you can enable drawing of an arrow from the text to the annotated

point by giving a dictionary of arrow properties in the optional keyword

argument *arrowprops*.

==================== =====================================================

*arrowprops* key description

==================== =====================================================

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

\*\*kwargs any key for :class:`matplotlib.patches.Polygon`,

e.g., ``facecolor``

==================== =====================================================

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 this example is placed in the

fractional figure coordinate system. :class:`matplotlib.text.Text`

keyword arguments like *horizontalalignment*, *verticalalignment* and

*fontsize* are passed from `~matplotlib.axes.Axes.annotate` to the

``Text`` instance.

.. figure:: ../../gallery/pyplots/images/sphx_glr_annotation_polar_001.png

:target: ../../gallery/pyplots/annotation_polar.html

:align: center

:scale: 50

Annotation Polar

For more on all the wild and wonderful things you can do with

annotations, including fancy arrows, see :ref:`plotting-guide-annotation`

and :doc:`/gallery/text_labels_and_annotations/annotation_demo`.

Do not proceed unless you have already read :ref:`annotations-tutorial`,

:func:`~matplotlib.pyplot.text` and :func:`~matplotlib.pyplot.annotate`!

.. _plotting-guide-annotation:

Advanced Annotations

--------------------

Annotating with Text with Box

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Let's start with a simple example.

.. figure:: ../../gallery/userdemo/images/sphx_glr_annotate_text_arrow_001.png

:target: ../../gallery/userdemo/annotate_text_arrow.html

:align: center

:scale: 50

Annotate Text Arrow

`~.Axes.text` takes a *bbox* keyword argument, which draws a box around the

text::

t = ax.text(

0, 0, "Direction", ha="center", va="center", rotation=45, size=15,

bbox=dict(boxstyle="rarrow,pad=0.3", fc="cyan", ec="b", lw=2))

The patch object associated with the text can be accessed by::

bb = t.get_bbox_patch()

The return value is a `.FancyBboxPatch`; patch properties

(facecolor, edgewidth, etc.) can be accessed and modified as usual.

`.FancyBboxPatch.set_boxstyle` sets the box shape::

bb.set_boxstyle("rarrow", pad=0.6)

The arguments are the name of the box style with its attributes as

keyword arguments. Currently, following box styles are implemented.

========== ============== ==========================

Class Name Attrs

========== ============== ==========================

Circle ``circle`` pad=0.3

DArrow ``darrow`` pad=0.3

LArrow ``larrow`` pad=0.3

RArrow ``rarrow`` pad=0.3

Round ``round`` pad=0.3,rounding_size=None

Round4 ``round4`` pad=0.3,rounding_size=None

Roundtooth ``roundtooth`` pad=0.3,tooth_size=None

Sawtooth ``sawtooth`` pad=0.3,tooth_size=None

Square ``square`` pad=0.3

========== ============== ==========================

.. figure:: ../../gallery/shapes_and_collections/images/sphx_glr_fancybox_demo_001.png

:target: ../../gallery/shapes_and_collections/fancybox_demo.html

:align: center

:scale: 50

Fancybox Demo

Note that the attribute arguments can be specified within the style

name with separating comma (this form can be used as "boxstyle" value

of bbox argument when initializing the text instance) ::

bb.set_boxstyle("rarrow,pad=0.6")

Annotating with Arrow

~~~~~~~~~~~~~~~~~~~~~

`~.Axes.annotate` draws an arrow connecting two points in an axes::

ax.annotate("Annotation",

xy=(x1, y1), xycoords='data',

xytext=(x2, y2), textcoords='offset points',

)

This annotates a point at *xy* in the given coordinate (*xycoords*)

with the text at *xytext* given in *textcoords*. Often, the

annotated point is specified in the *data* coordinate and the annotating

text in *offset points*.

See `~.Axes.annotate` for available coordinate systems.

An arrow connecting *xy* to *xytext* can be optionally drawn by

specifying the *arrowprops* argument. To draw only an arrow, use

empty string as the first argument. ::

ax.annotate("",

xy=(0.2, 0.2), xycoords='data',

xytext=(0.8, 0.8), textcoords='data',

arrowprops=dict(arrowstyle="->",

connectionstyle="arc3"),

)

.. figure:: ../../gallery/userdemo/images/sphx_glr_annotate_simple01_001.png

:target: ../../gallery/userdemo/annotate_simple01.html

:align: center

:scale: 50

Annotate Simple01

The arrow is drawn as follows:

1. A path connecting the two points is created, as specified by the

*connectionstyle* parameter.

2. The path is clipped to avoid patches *patchA* and *patchB*, if these are

set.

3. The path is further shrunk by *shrinkA* and *shrinkB* (in pixels).

4. The path is transmuted to an arrow patch, as specified by the *arrowstyle*

parameter.

.. figure:: ../../gallery/userdemo/images/sphx_glr_annotate_explain_001.png

:target: ../../gallery/userdemo/annotate_explain.html

:align: center

:scale: 50

Annotate Explain

The creation of the connecting path between two points is controlled by

``connectionstyle`` key and the following styles are available.

========== =============================================

Name Attrs

========== =============================================

``angle`` angleA=90,angleB=0,rad=0.0

``angle3`` angleA=90,angleB=0

``arc`` angleA=0,angleB=0,armA=None,armB=None,rad=0.0

``arc3`` rad=0.0

``bar`` armA=0.0,armB=0.0,fraction=0.3,angle=None

========== =============================================

Note that "3" in ``angle3`` and ``arc3`` is meant to indicate that the

resulting path is a quadratic spline segment (three control

points). As will be discussed below, some arrow style options can only

be used when the connecting path is a quadratic spline.

The behavior of each connection style is (limitedly) demonstrated in the

example below. (Warning: The behavior of the ``bar`` style is currently not

well defined, it may be changed in the future).

.. figure:: ../../gallery/userdemo/images/sphx_glr_connectionstyle_demo_001.png

:target: ../../gallery/userdemo/connectionstyle_demo.html

:align: center

:scale: 50

Connectionstyle Demo

The connecting path (after clipping and shrinking) is then mutated to

an arrow patch, according to the given ``arrowstyle``.

========== =============================================

Name Attrs

========== =============================================

``-`` None

``->`` head_length=0.4,head_width=0.2

``-[`` widthB=1.0,lengthB=0.2,angleB=None

``|-|`` widthA=1.0,widthB=1.0

``-|>`` head_length=0.4,head_width=0.2

``<-`` head_length=0.4,head_width=0.2

``<->`` head_length=0.4,head_width=0.2

``<|-`` head_length=0.4,head_width=0.2

``<|-|>`` head_length=0.4,head_width=0.2

``fancy`` head_length=0.4,head_width=0.4,tail_width=0.4

``simple`` head_length=0.5,head_width=0.5,tail_width=0.2

``wedge`` tail_width=0.3,shrink_factor=0.5

========== =============================================

.. figure:: ../../gallery/text_labels_and_annotations/images/sphx_glr_fancyarrow_demo_001.png

:target: ../../gallery/text_labels_and_annotations/fancyarrow_demo.html

:align: center

:scale: 50

Fancyarrow Demo

Some arrowstyles only work with connection styles that generate a

quadratic-spline segment. They are ``fancy``, ``simple``, and ``wedge``.

For these arrow styles, you must use the "angle3" or "arc3" connection

style.

If the annotation string is given, the patchA is set to the bbox patch

of the text by default.

.. figure:: ../../gallery/userdemo/images/sphx_glr_annotate_simple02_001.png

:target: ../../gallery/userdemo/annotate_simple02.html

:align: center

:scale: 50

Annotate Simple02

As with `~.Axes.text`, a box around the text can be drawn using the *bbox*

argument.

.. figure:: ../../gallery/userdemo/images/sphx_glr_annotate_simple03_001.png

:target: ../../gallery/userdemo/annotate_simple03.html

:align: center

:scale: 50

Annotate Simple03

By default, the starting point is set to the center of the text

extent. This can be adjusted with ``relpos`` key value. The values

are normalized to the extent of the text. For example, (0, 0) means

lower-left corner and (1, 1) means top-right.

.. figure:: ../../gallery/userdemo/images/sphx_glr_annotate_simple04_001.png

:target: ../../gallery/userdemo/annotate_simple04.html

:align: center

:scale: 50

Annotate Simple04

Placing Artist at the anchored location of the Axes

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

There are classes of artists that can be placed at an anchored

location in the Axes. A common example is the legend. This type

of artist can be created by using the `.OffsetBox` class. A few

predefined classes are available in :mod:`matplotlib.offsetbox` and in

:mod:`mpl_toolkits.axes_grid1.anchored_artists`. ::

from matplotlib.offsetbox import AnchoredText

at = AnchoredText("Figure 1a",

prop=dict(size=15), frameon=True,

loc='upper left',

)

at.patch.set_boxstyle("round,pad=0.,rounding_size=0.2")

ax.add_artist(at)

.. figure:: ../../gallery/userdemo/images/sphx_glr_anchored_box01_001.png

:target: ../../gallery/userdemo/anchored_box01.html

:align: center

:scale: 50

Anchored Box01

The *loc* keyword has same meaning as in the legend command.

A simple application is when the size of the artist (or collection of

artists) is known in pixel size during the time of creation. For

example, If you want to draw a circle with fixed size of 20 pixel x 20

pixel (radius = 10 pixel), you can utilize

``AnchoredDrawingArea``. The instance is created with a size of the

drawing area (in pixels), and arbitrary artists can added to the

drawing area. Note that the extents of the artists that are added to

the drawing area are not related to the placement of the drawing

area itself. Only the initial size matters. ::

from mpl_toolkits.axes_grid1.anchored_artists import AnchoredDrawingArea

ada = AnchoredDrawingArea(20, 20, 0, 0,

loc='upper right', pad=0., frameon=False)

p1 = Circle((10, 10), 10)

ada.drawing_area.add_artist(p1)

p2 = Circle((30, 10), 5, fc="r")

ada.drawing_area.add_artist(p2)

The artists that are added to the drawing area should not have a

transform set (it will be overridden) and the dimensions of those

artists are interpreted as a pixel coordinate, i.e., the radius of the

circles in above example are 10 pixels and 5 pixels, respectively.

.. figure:: ../../gallery/userdemo/images/sphx_glr_anchored_box02_001.png

:target: ../../gallery/userdemo/anchored_box02.html

:align: center

:scale: 50

Anchored Box02

Sometimes, you want your artists to scale with the data coordinate (or

coordinates other than canvas pixels). You can use

``AnchoredAuxTransformBox`` class. This is similar to

``AnchoredDrawingArea`` except that the extent of the artist is

determined during the drawing time respecting the specified transform. ::

from mpl_toolkits.axes_grid1.anchored_artists import AnchoredAuxTransformBox

box = AnchoredAuxTransformBox(ax.transData, loc='upper left')

el = Ellipse((0, 0), width=0.1, height=0.4, angle=30) # in data coordinates!

box.drawing_area.add_artist(el)

The ellipse in the above example will have width and height

corresponding to 0.1 and 0.4 in data coordinates and will be

automatically scaled when the view limits of the axes change.

.. figure:: ../../gallery/userdemo/images/sphx_glr_anchored_box03_001.png

:target: ../../gallery/userdemo/anchored_box03.html

:align: center

:scale: 50

Anchored Box03

As in the legend, the bbox_to_anchor argument can be set. Using the

HPacker and VPacker, you can have an arrangement(?) of artist as in the

legend (as a matter of fact, this is how the legend is created).

.. figure:: ../../gallery/userdemo/images/sphx_glr_anchored_box04_001.png

:target: ../../gallery/userdemo/anchored_box04.html

:align: center

:scale: 50

Anchored Box04

Note that unlike the legend, the ``bbox_transform`` is set

to IdentityTransform by default.

Using Complex Coordinates with Annotations

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Annotation in matplotlib supports several types of coordinates as

described in :ref:`annotations-tutorial`. For an advanced user who wants

more control, it supports a few other options.

1. A `.Transform` instance. For example, ::

ax.annotate("Test", xy=(0.5, 0.5), xycoords=ax.transAxes)

is identical to ::

ax.annotate("Test", xy=(0.5, 0.5), xycoords="axes fraction")

This allows annotating a point in another axes::

ax1, ax2 = subplot(121), subplot(122)

ax2.annotate("Test", xy=(0.5, 0.5), xycoords=ax1.transData,

xytext=(0.5, 0.5), textcoords=ax2.transData,

arrowprops=dict(arrowstyle="->"))

2. An `.Artist` instance. The *xy* value (or *xytext*) is interpreted as a

fractional coordinate of the bbox (return value of *get_window_extent*) of

the artist::

an1 = ax.annotate("Test 1", xy=(0.5, 0.5), xycoords="data",

va="center", ha="center",

bbox=dict(boxstyle="round", fc="w"))

an2 = ax.annotate("Test 2", xy=(1, 0.5), xycoords=an1, # (1, 0.5) of the an1's bbox

xytext=(30, 0), textcoords="offset points",

va="center", ha="left",

bbox=dict(boxstyle="round", fc="w"),

arrowprops=dict(arrowstyle="->"))

.. figure:: ../../gallery/userdemo/images/sphx_glr_annotate_simple_coord01_001.png

:target: ../../gallery/userdemo/annotate_simple_coord01.html

:align: center

:scale: 50

Annotation with Simple Coordinates

Note that you must ensure that the extent of the coordinate artist (*an1* in

above example) is determined before *an2* gets drawn. Usually, this means

that *an2* needs to be drawn after *an1*.

3. A callable object that takes the renderer instance as single argument, and

returns either a `.Transform` or a `.BboxBase`. The return value is then

handled as in (1), for transforms, or in (2), for bboxes. For example, ::

an2 = ax.annotate("Test 2", xy=(1, 0.5), xycoords=an1,

xytext=(30, 0), textcoords="offset points")

is identical to::

an2 = ax.annotate("Test 2", xy=(1, 0.5), xycoords=an1.get_window_extent,

xytext=(30, 0), textcoords="offset points")

4. A pair of coordinate specifications -- the first for the x-coordinate, and

the second is for the y-coordinate; e.g. ::

annotate("Test", xy=(0.5, 1), xycoords=("data", "axes fraction"))

Here, 0.5 is in data coordinates, and 1 is in normalized axes coordinates.

Each of the coordinate specifications can also be an artist or a transform.

For example,

.. figure:: ../../gallery/userdemo/images/sphx_glr_annotate_simple_coord02_001.png

:target: ../../gallery/userdemo/annotate_simple_coord02.html

:align: center

:scale: 50

Annotation with Simple Coordinates 2

5. Sometimes, you want your annotation with some "offset points", not from the

annotated point but from some other point. `.text.OffsetFrom` is a helper

for such cases.

.. figure:: ../../gallery/userdemo/images/sphx_glr_annotate_simple_coord03_001.png

:target: ../../gallery/userdemo/annotate_simple_coord03.html

:align: center

:scale: 50

Annotation with Simple Coordinates 3

You may take a look at this example

:doc:`/gallery/text_labels_and_annotations/annotation_demo`.

Using ConnectionPatch

~~~~~~~~~~~~~~~~~~~~~

ConnectionPatch is like an annotation without text. While `~.Axes.annotate`

is sufficient in most situations, ConnectionPatch is useful when you want to

connect points in different axes. ::

from matplotlib.patches import ConnectionPatch

xy = (0.2, 0.2)

con = ConnectionPatch(xyA=xy, coordsA=ax1.transData,

xyB=xy, coordsB=ax2.transData)

fig.add_artist(con)

The above code connects point *xy* in the data coordinates of ``ax1`` to

point *xy* in the data coordinates of ``ax2``. Here is a simple example.

.. figure:: ../../gallery/userdemo/images/sphx_glr_connect_simple01_001.png

:target: ../../gallery/userdemo/connect_simple01.html

:align: center

:scale: 50

Connect Simple01

Here, we added the ConnectionPatch to the *figure* (with `~.Figure.add_artist`)

rather than to either axes: this ensures that it is drawn on top of both axes,

and is also necessary if using :doc:`constrained_layout

</tutorials/intermediate/constrainedlayout_guide>` for positioning the axes.

Advanced Topics

---------------

Zoom effect between Axes

~~~~~~~~~~~~~~~~~~~~~~~~

``mpl_toolkits.axes_grid1.inset_locator`` defines some patch classes useful for

interconnecting two axes. Understanding the code requires some knowledge of

Matplotlib's transform system.

.. figure:: ../../gallery/subplots_axes_and_figures/images/sphx_glr_axes_zoom_effect_001.png

:target: ../../gallery/subplots_axes_and_figures/axes_zoom_effect.html

:align: center

:scale: 50

Axes Zoom Effect

Define Custom BoxStyle

~~~~~~~~~~~~~~~~~~~~~~

You can use a custom box style. The value for the ``boxstyle`` can be a

callable object in the following forms.::

def __call__(self, x0, y0, width, height, mutation_size,

aspect_ratio=1.):

'''

Given the location and size of the box, return the path of

the box around it.

- *x0*, *y0*, *width*, *height* : location and size of the box

- *mutation_size* : a reference scale for the mutation.

- *aspect_ratio* : aspect-ratio for the mutation.

'''

path = ...

return path

Here is a complete example.

.. figure:: ../../gallery/userdemo/images/sphx_glr_custom_boxstyle01_001.png

:target: ../../gallery/userdemo/custom_boxstyle01.html

:align: center

:scale: 50

Custom Boxstyle01

Similarly, you can define a custom ConnectionStyle and a custom ArrowStyle.

See the source code of ``lib/matplotlib/patches.py`` and check

how each style class is defined.

"""

matplotlib/tutorials/text/annotations.py at v3.3.x · matplotlib/matplotlib · GitHub

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