注释图
以下示例显示了如何在matplotlib中注释绘图。这包括突出显示特定的兴趣点，并使用各种视觉工具来引起对这一点的关注。有关matplotlib中注释和文本工具的更完整和深入的描述，请参阅注释教程。
import matplotlib.pyplot as plt
from matplotlib.patches import Ellipse
import numpy as np
from matplotlib.text import OffsetFrom
指定文本点和注释点
您必须指定注释点 xy = (x, y) 来注释此点。另外，您可以为此注释的文本位置指定文本点 xytext=(x, y)。 （可选）您可以使用xycoords和textcoords的以下字符串之一指定xy和xytext的坐标系（默认为'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
注意：对于物理坐标系（点或像素），原点是图形或轴的（底部，左侧）。
（可选）您可以通过提供箭头属性字典来指定箭头属性，该属性可以从文本绘制和箭头到注释点
有效关键点是：
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)
# Create our figure and data we'll use for plotting
fig, ax = plt.subplots(figsize=(3, 3))
t = np.arange(0.0, 5.0, 0.01)
s = np.cos(2*np.pi*t)
# Plot a line and add some simple annotations
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('figure fraction',
xy=(.025, .975), xycoords='figure fraction',
horizontalalignment='left', verticalalignment='top',
fontsize=20)
# The following examples show off how these arrows are drawn.
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')
# You may also use negative points or pixels to specify from (right, top).
# E.g., (-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')
ax.set(xlim=(-1, 5), ylim=(-3, 5))
使用多个坐标系和轴类型
您可以在不同位置和坐标系中指定xypoint和xytext，也可以选择打开连接线并使用标记标记点。 注释也适用于极轴。
在下面的示例中，xy点是本机坐标（xycoords默认为'data'）。对于极轴，这是在（θ，半径）空间中。示例中的文本放在小数字坐标系中。文本关键字args如水平和垂直对齐被尊重。
fig, ax = plt.subplots(subplot_kw=dict(projection='polar'), figsize=(3, 3))
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, ax = plt.subplots(subplot_kw=dict(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], ylim=[-20, 20])
自定义箭头和气泡样式
xytext和注释点之间的箭头以及覆盖注释文本的气泡可高度自定义。 下面是一些参数选项以及它们的结果输出。
fig, ax = plt.subplots(figsize=(8, 5))
t = np.arange(0.0, 5.0, 0.01)
s = np.cos(2*np.pi*t)
line, = ax.plot(t, s, lw=3)
ax.annotate('straight',
xy=(0, 1), xycoords='data',
xytext=(-50, 30), textcoords='offset points',
arrowprops=dict(arrowstyle="->"))
ax.annotate('arc3,\nrad 0.2',
xy=(0.5, -1), xycoords='data',
xytext=(-80, -60), textcoords='offset points',
arrowprops=dict(arrowstyle="->",
connectionstyle="arc3,rad=.2"))
ax.annotate('arc,\nangle 50',
xy=(1., 1), xycoords='data',
xytext=(-90, 50), textcoords='offset points',
arrowprops=dict(arrowstyle="->",
connectionstyle="arc,angleA=0,armA=50,rad=10"))
ax.annotate('arc,\narms',
xy=(1.5, -1), xycoords='data',
xytext=(-80, -60), textcoords='offset points',
arrowprops=dict(arrowstyle="->",
connectionstyle="arc,angleA=0,armA=40,angleB=-90,armB=30,rad=7"))
ax.annotate('angle,\nangle 90',
xy=(2., 1), xycoords='data',
xytext=(-70, 30), textcoords='offset points',
arrowprops=dict(arrowstyle="->",
connectionstyle="angle,angleA=0,angleB=90,rad=10"))
ax.annotate('angle3,\nangle -90',
xy=(2.5, -1), xycoords='data',
xytext=(-80, -60), textcoords='offset points',
arrowprops=dict(arrowstyle="->",
connectionstyle="angle3,angleA=0,angleB=-90"))
ax.annotate('angle,\nround',
xy=(3., 1), xycoords='data',
xytext=(-60, 30), textcoords='offset points',
bbox=dict(boxstyle="round", fc="0.8"),
arrowprops=dict(arrowstyle="->",
connectionstyle="angle,angleA=0,angleB=90,rad=10"))
ax.annotate('angle,\nround4',
xy=(3.5, -1), xycoords='data',
xytext=(-70, -80), textcoords='offset points',
size=20,
bbox=dict(boxstyle="round4,pad=.5", fc="0.8"),
arrowprops=dict(arrowstyle="->",
connectionstyle="angle,angleA=0,angleB=-90,rad=10"))
ax.annotate('angle,\nshrink',
xy=(4., 1), xycoords='data',
xytext=(-60, 30), textcoords='offset points',
bbox=dict(boxstyle="round", fc="0.8"),
arrowprops=dict(arrowstyle="->",
shrinkA=0, shrinkB=10,
connectionstyle="angle,angleA=0,angleB=90,rad=10"))
# You can pass an empty string to get only annotation arrows rendered
ann = ax.annotate('', xy=(4., 1.), xycoords='data',
xytext=(4.5, -1), textcoords='data',
arrowprops=dict(arrowstyle="<->",
connectionstyle="bar",
ec="k",
shrinkA=5, shrinkB=5))
ax.set(xlim=(-1, 5), ylim=(-4, 3))
# We'll create another figure so that it doesn't get too cluttered
fig, ax = plt.subplots()
el = Ellipse((2, -1), 0.5, 0.5)
ax.add_patch(el)
ax.annotate('$->$',
xy=(2., -1), xycoords='data',
xytext=(-150, -140), textcoords='offset points',
bbox=dict(boxstyle="round", fc="0.8"),
arrowprops=dict(arrowstyle="->",
patchB=el,
connectionstyle="angle,angleA=90,angleB=0,rad=10"))
ax.annotate('arrow\nfancy',
xy=(2., -1), xycoords='data',
xytext=(-100, 60), textcoords='offset points',
size=20,
# bbox=dict(boxstyle="round", fc="0.8"),
arrowprops=dict(arrowstyle="fancy",
fc="0.6", ec="none",
patchB=el,
connectionstyle="angle3,angleA=0,angleB=-90"))
ax.annotate('arrow\nsimple',
xy=(2., -1), xycoords='data',
xytext=(100, 60), textcoords='offset points',
size=20,
# bbox=dict(boxstyle="round", fc="0.8"),
arrowprops=dict(arrowstyle="simple",
fc="0.6", ec="none",
patchB=el,
connectionstyle="arc3,rad=0.3"))
ax.annotate('wedge',
xy=(2., -1), xycoords='data',
xytext=(-100, -100), textcoords='offset points',
size=20,
# bbox=dict(boxstyle="round", fc="0.8"),
arrowprops=dict(arrowstyle="wedge,tail_width=0.7",
fc="0.6", ec="none",
patchB=el,
connectionstyle="arc3,rad=-0.3"))
ann = ax.annotate('bubble,\ncontours',
xy=(2., -1), xycoords='data',
xytext=(0, -70), textcoords='offset points',
size=20,
bbox=dict(boxstyle="round",
fc=(1.0, 0.7, 0.7),
ec=(1., .5, .5)),
arrowprops=dict(arrowstyle="wedge,tail_width=1.",
fc=(1.0, 0.7, 0.7), ec=(1., .5, .5),
patchA=None,
patchB=el,
relpos=(0.2, 0.8),
connectionstyle="arc3,rad=-0.1"))
ann = ax.annotate('bubble',
xy=(2., -1), xycoords='data',
xytext=(55, 0), textcoords='offset points',
size=20, va="center",
bbox=dict(boxstyle="round", fc=(1.0, 0.7, 0.7), ec="none"),
arrowprops=dict(arrowstyle="wedge,tail_width=1.",
fc=(1.0, 0.7, 0.7), ec="none",
patchA=None,
patchB=el,
relpos=(0.2, 0.5)))
ax.set(xlim=(-1, 5), ylim=(-5, 3))
更多坐标系的例子
下面我们将展示几个坐标系的例子，以及如何指定注释的位置。
fig, (ax1, ax2) = plt.subplots(1, 2)
bbox_args = dict(boxstyle="round", fc="0.8")
arrow_args = dict(arrowstyle="->")
# Here we'll demonstrate the extents of the coordinate system and how
# we place annotating text.
ax1.annotate('figure fraction : 0, 0', xy=(0, 0), xycoords='figure fraction',
xytext=(20, 20), textcoords='offset points',
ha="left", va="bottom",
bbox=bbox_args,
arrowprops=arrow_args)
ax1.annotate('figure fraction : 1, 1', xy=(1, 1), xycoords='figure fraction',
xytext=(-20, -20), textcoords='offset points',
ha="right", va="top",
bbox=bbox_args,
arrowprops=arrow_args)
ax1.annotate('axes fraction : 0, 0', xy=(0, 0), xycoords='axes fraction',
xytext=(20, 20), textcoords='offset points',
ha="left", va="bottom",
bbox=bbox_args,
arrowprops=arrow_args)
ax1.annotate('axes fraction : 1, 1', xy=(1, 1), xycoords='axes fraction',
xytext=(-20, -20), textcoords='offset points',
ha="right", va="top",
bbox=bbox_args,
arrowprops=arrow_args)
# It is also possible to generate draggable annotations
an1 = ax1.annotate('Drag me 1', xy=(.5, .7), xycoords='data',
#xytext=(.5, .7), textcoords='data',
ha="center", va="center",
bbox=bbox_args,
#arrowprops=arrow_args
)
an2 = ax1.annotate('Drag me 2', xy=(.5, .5), xycoords=an1,
xytext=(.5, .3), textcoords='axes fraction',
ha="center", va="center",
bbox=bbox_args,
arrowprops=dict(patchB=an1.get_bbox_patch(),
connectionstyle="arc3,rad=0.2",
**arrow_args))
an1.draggable()
an2.draggable()
an3 = ax1.annotate('', xy=(.5, .5), xycoords=an2,
xytext=(.5, .5), textcoords=an1,
ha="center", va="center",
bbox=bbox_args,
arrowprops=dict(patchA=an1.get_bbox_patch(),
patchB=an2.get_bbox_patch(),
connectionstyle="arc3,rad=0.2",
**arrow_args))
# Finally we'll show off some more complex annotation and placement
text = ax2.annotate('xy=(0, 1)\nxycoords=("data", "axes fraction")',
xy=(0, 1), xycoords=("data", 'axes fraction'),
xytext=(0, -20), textcoords='offset points',
ha="center", va="top",
bbox=bbox_args,
arrowprops=arrow_args)
ax2.annotate('xy=(0.5, 0)\nxycoords=artist',
xy=(0.5, 0.), xycoords=text,
xytext=(0, -20), textcoords='offset points',
ha="center", va="top",
bbox=bbox_args,
arrowprops=arrow_args)
ax2.annotate('xy=(0.8, 0.5)\nxycoords=ax1.transData',
xy=(0.8, 0.5), xycoords=ax1.transData,
xytext=(10, 10),
textcoords=OffsetFrom(ax2.bbox, (0, 0), "points"),
ha="left", va="bottom",
bbox=bbox_args,
arrowprops=arrow_args)
ax2.set(xlim=[-2, 2], ylim=[-2, 2])
plt.show()
