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。

  1. import matplotlib.pyplot as plt
  2. from matplotlib.patches import Ellipse
  3. import numpy as np
  4. 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’）：

  1. 'figure points'   : points from the lower left corner of the figure
  2. 'figure pixels'   : pixels from the lower left corner of the figure
  3. 'figure fraction' : 0,0 is lower left of figure and 1,1 is upper, right
  4. 'axes points'     : points from lower left corner of axes
  5. 'axes pixels'     : pixels from lower left corner of axes
  6. 'axes fraction'   : 0,0 is lower left of axes and 1,1 is upper right
  7. 'offset points'   : Specify an offset (in points) from the xy value
  8. 'offset pixels'   : Specify an offset (in pixels) from the xy value
  9. '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：

  1. width : the width of the arrow in points
  2. frac  : the fraction of the arrow length occupied by the head
  3. headwidth : the width of the base of the arrow head in points
  4. shrink : move the tip and base some percent away from the
  5.          annotated point and text
  6. any key for matplotlib.patches.polygon  (e.g., facecolor)
  1. # Create our figure and data we'll use for plotting
  2. fig, ax = plt.subplots(figsize=(3, 3))
  4. t = np.arange(0.0, 5.0, 0.01)
  5. s = np.cos(2*np.pi*t)
  7. # Plot a line and add some simple annotations
  8. line, = ax.plot(t, s)
  9. ax.annotate('figure pixels',
  10.             xy=(10, 10), xycoords='figure pixels')
  11. ax.annotate('figure points',
  12.             xy=(80, 80), xycoords='figure points')
  13. ax.annotate('figure fraction',
  14.             xy=(.025, .975), xycoords='figure fraction',
  15.             horizontalalignment='left', verticalalignment='top',
  16.             fontsize=20)
  18. # The following examples show off how these arrows are drawn.
  20. ax.annotate('point offset from data',
  21.             xy=(2, 1), xycoords='data',
  22.             xytext=(-15, 25), textcoords='offset points',
  23.             arrowprops=dict(facecolor='black', shrink=0.05),
  24.             horizontalalignment='right', verticalalignment='bottom')
  26. ax.annotate('axes fraction',
  27.             xy=(3, 1), xycoords='data',
  28.             xytext=(0.8, 0.95), textcoords='axes fraction',
  29.             arrowprops=dict(facecolor='black', shrink=0.05),
  30.             horizontalalignment='right', verticalalignment='top')
  32. # You may also use negative points or pixels to specify from (right, top).
  33. # E.g., (-10, 10) is 10 points to the left of the right side of the axes and 10
  34. # points above the bottom
  36. ax.annotate('pixel offset from axes fraction',
  37.             xy=(1, 0), xycoords='axes fraction',
  38.             xytext=(-20, 20), textcoords='offset pixels',
  39.             horizontalalignment='right',
  40.             verticalalignment='bottom')
  42. ax.set(xlim=(-1, 5), ylim=(-3, 5))

注释图示例

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。

  1. fig, ax = plt.subplots(subplot_kw=dict(projection='polar'), figsize=(3, 3))
  2. r = np.arange(0, 1, 0.001)
  3. theta = 2*2*np.pi*r
  4. line, = ax.plot(theta, r)
  6. ind = 800
  7. thisr, thistheta = r[ind], theta[ind]
  8. ax.plot([thistheta], [thisr], 'o')
  9. ax.annotate('a polar annotation',
  10.             xy=(thistheta, thisr),  # theta, radius
  11.             xytext=(0.05, 0.05),    # fraction, fraction
  12.             textcoords='figure fraction',
  13.             arrowprops=dict(facecolor='black', shrink=0.05),
  14.             horizontalalignment='left',
  15.             verticalalignment='bottom')
  17. # You can also use polar notation on a cartesian axes.  Here the native
  18. # coordinate system ('data') is cartesian, so you need to specify the
  19. # xycoords and textcoords as 'polar' if you want to use (theta, radius).
  21. el = Ellipse((0, 0), 10, 20, facecolor='r', alpha=0.5)
  23. fig, ax = plt.subplots(subplot_kw=dict(aspect='equal'))
  24. ax.add_artist(el)
  25. el.set_clip_box(ax.bbox)
  26. ax.annotate('the top',
  27.             xy=(np.pi/2., 10.),      # theta, radius
  28.             xytext=(np.pi/3, 20.),   # theta, radius
  29.             xycoords='polar',
  30.             textcoords='polar',
  31.             arrowprops=dict(facecolor='black', shrink=0.05),
  32.             horizontalalignment='left',
  33.             verticalalignment='bottom',
  34.             clip_on=True)  # clip to the axes bounding box
  36. ax.set(xlim=[-20, 20], ylim=[-20, 20])

注释图示例2

注释图示例3

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。

  1. fig, ax = plt.subplots(figsize=(8, 5))
  3. t = np.arange(0.0, 5.0, 0.01)
  4. s = np.cos(2*np.pi*t)
  5. line, = ax.plot(t, s, lw=3)
  7. ax.annotate('straight',
  8.             xy=(0, 1), xycoords='data',
  9.             xytext=(-50, 30), textcoords='offset points',
  10.             arrowprops=dict(arrowstyle="->"))
  12. ax.annotate('arc3,\nrad 0.2',
  13.             xy=(0.5, -1), xycoords='data',
  14.             xytext=(-80, -60), textcoords='offset points',
  15.             arrowprops=dict(arrowstyle="->",
  16.                             connectionstyle="arc3,rad=.2"))
  18. ax.annotate('arc,\nangle 50',
  19.             xy=(1., 1), xycoords='data',
  20.             xytext=(-90, 50), textcoords='offset points',
  21.             arrowprops=dict(arrowstyle="->",
  22.                             connectionstyle="arc,angleA=0,armA=50,rad=10"))
  24. ax.annotate('arc,\narms',
  25.             xy=(1.5, -1), xycoords='data',
  26.             xytext=(-80, -60), textcoords='offset points',
  27.             arrowprops=dict(arrowstyle="->",
  28.                             connectionstyle="arc,angleA=0,armA=40,angleB=-90,armB=30,rad=7"))
  30. ax.annotate('angle,\nangle 90',
  31.             xy=(2., 1), xycoords='data',
  32.             xytext=(-70, 30), textcoords='offset points',
  33.             arrowprops=dict(arrowstyle="->",
  34.                             connectionstyle="angle,angleA=0,angleB=90,rad=10"))
  36. ax.annotate('angle3,\nangle -90',
  37.             xy=(2.5, -1), xycoords='data',
  38.             xytext=(-80, -60), textcoords='offset points',
  39.             arrowprops=dict(arrowstyle="->",
  40.                             connectionstyle="angle3,angleA=0,angleB=-90"))
  42. ax.annotate('angle,\nround',
  43.             xy=(3., 1), xycoords='data',
  44.             xytext=(-60, 30), textcoords='offset points',
  45.             bbox=dict(boxstyle="round", fc="0.8"),
  46.             arrowprops=dict(arrowstyle="->",
  47.                             connectionstyle="angle,angleA=0,angleB=90,rad=10"))
  49. ax.annotate('angle,\nround4',
  50.             xy=(3.5, -1), xycoords='data',
  51.             xytext=(-70, -80), textcoords='offset points',
  52.             size=20,
  53.             bbox=dict(boxstyle="round4,pad=.5", fc="0.8"),
  54.             arrowprops=dict(arrowstyle="->",
  55.                             connectionstyle="angle,angleA=0,angleB=-90,rad=10"))
  57. ax.annotate('angle,\nshrink',
  58.             xy=(4., 1), xycoords='data',
  59.             xytext=(-60, 30), textcoords='offset points',
  60.             bbox=dict(boxstyle="round", fc="0.8"),
  61.             arrowprops=dict(arrowstyle="->",
  62.                             shrinkA=0, shrinkB=10,
  63.                             connectionstyle="angle,angleA=0,angleB=90,rad=10"))
  65. # You can pass an empty string to get only annotation arrows rendered
  66. ann = ax.annotate('', xy=(4., 1.), xycoords='data',
  67.                   xytext=(4.5, -1), textcoords='data',
  68.                   arrowprops=dict(arrowstyle="<->",
  69.                                   connectionstyle="bar",
  70.                                   ec="k",
  71.                                   shrinkA=5, shrinkB=5))
  73. ax.set(xlim=(-1, 5), ylim=(-4, 3))
  75. # We'll create another figure so that it doesn't get too cluttered
  76. fig, ax = plt.subplots()
  78. el = Ellipse((2, -1), 0.5, 0.5)
  79. ax.add_patch(el)
  81. ax.annotate('$->$',
  82.             xy=(2., -1), xycoords='data',
  83.             xytext=(-150, -140), textcoords='offset points',
  84.             bbox=dict(boxstyle="round", fc="0.8"),
  85.             arrowprops=dict(arrowstyle="->",
  86.                             patchB=el,
  87.                             connectionstyle="angle,angleA=90,angleB=0,rad=10"))
  89. ax.annotate('arrow\nfancy',
  90.             xy=(2., -1), xycoords='data',
  91.             xytext=(-100, 60), textcoords='offset points',
  92.             size=20,
  93.             # bbox=dict(boxstyle="round", fc="0.8"),
  94.             arrowprops=dict(arrowstyle="fancy",
  95.                             fc="0.6", ec="none",
  96.                             patchB=el,
  97.                             connectionstyle="angle3,angleA=0,angleB=-90"))
  99. ax.annotate('arrow\nsimple',
  100.             xy=(2., -1), xycoords='data',
  101.             xytext=(100, 60), textcoords='offset points',
  102.             size=20,
  103.             # bbox=dict(boxstyle="round", fc="0.8"),
  104.             arrowprops=dict(arrowstyle="simple",
  105.                             fc="0.6", ec="none",
  106.                             patchB=el,
  107.                             connectionstyle="arc3,rad=0.3"))
  109. ax.annotate('wedge',
  110.             xy=(2., -1), xycoords='data',
  111.             xytext=(-100, -100), textcoords='offset points',
  112.             size=20,
  113.             # bbox=dict(boxstyle="round", fc="0.8"),
  114.             arrowprops=dict(arrowstyle="wedge,tail_width=0.7",
  115.                             fc="0.6", ec="none",
  116.                             patchB=el,
  117.                             connectionstyle="arc3,rad=-0.3"))
  119. ann = ax.annotate('bubble,\ncontours',
  120.                   xy=(2., -1), xycoords='data',
  121.                   xytext=(0, -70), textcoords='offset points',
  122.                   size=20,
  123.                   bbox=dict(boxstyle="round",
  124.                             fc=(1.0, 0.7, 0.7),
  125.                             ec=(1., .5, .5)),
  126.                   arrowprops=dict(arrowstyle="wedge,tail_width=1.",
  127.                                   fc=(1.0, 0.7, 0.7), ec=(1., .5, .5),
  128.                                   patchA=None,
  129.                                   patchB=el,
  130.                                   relpos=(0.2, 0.8),
  131.                                   connectionstyle="arc3,rad=-0.1"))
  133. ann = ax.annotate('bubble',
  134.                   xy=(2., -1), xycoords='data',
  135.                   xytext=(55, 0), textcoords='offset points',
  136.                   size=20, va="center",
  137.                   bbox=dict(boxstyle="round", fc=(1.0, 0.7, 0.7), ec="none"),
  138.                   arrowprops=dict(arrowstyle="wedge,tail_width=1.",
  139.                                   fc=(1.0, 0.7, 0.7), ec="none",
  140.                                   patchA=None,
  141.                                   patchB=el,
  142.                                   relpos=(0.2, 0.5)))
  144. ax.set(xlim=(-1, 5), ylim=(-5, 3))

注释图示例4

注释图示例5

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。

  1. fig, (ax1, ax2) = plt.subplots(1, 2)
  3. bbox_args = dict(boxstyle="round", fc="0.8")
  4. arrow_args = dict(arrowstyle="->")
  6. # Here we'll demonstrate the extents of the coordinate system and how
  7. # we place annotating text.
  9. ax1.annotate('figure fraction : 0, 0', xy=(0, 0), xycoords='figure fraction',
  10.              xytext=(20, 20), textcoords='offset points',
  11.              ha="left", va="bottom",
  12.              bbox=bbox_args,
  13.              arrowprops=arrow_args)
  15. ax1.annotate('figure fraction : 1, 1', xy=(1, 1), xycoords='figure fraction',
  16.              xytext=(-20, -20), textcoords='offset points',
  17.              ha="right", va="top",
  18.              bbox=bbox_args,
  19.              arrowprops=arrow_args)
  21. ax1.annotate('axes fraction : 0, 0', xy=(0, 0), xycoords='axes fraction',
  22.              xytext=(20, 20), textcoords='offset points',
  23.              ha="left", va="bottom",
  24.              bbox=bbox_args,
  25.              arrowprops=arrow_args)
  27. ax1.annotate('axes fraction : 1, 1', xy=(1, 1), xycoords='axes fraction',
  28.              xytext=(-20, -20), textcoords='offset points',
  29.              ha="right", va="top",
  30.              bbox=bbox_args,
  31.              arrowprops=arrow_args)
  33. # It is also possible to generate draggable annotations
  35. an1 = ax1.annotate('Drag me 1', xy=(.5, .7), xycoords='data',
  36.                    #xytext=(.5, .7), textcoords='data',
  37.                    ha="center", va="center",
  38.                    bbox=bbox_args,
  39.                    #arrowprops=arrow_args
  40.                    )
  42. an2 = ax1.annotate('Drag me 2', xy=(.5, .5), xycoords=an1,
  43.                    xytext=(.5, .3), textcoords='axes fraction',
  44.                    ha="center", va="center",
  45.                    bbox=bbox_args,
  46.                    arrowprops=dict(patchB=an1.get_bbox_patch(),
  47.                                    connectionstyle="arc3,rad=0.2",
  48.                                    **arrow_args))
  49. an1.draggable()
  50. an2.draggable()
  52. an3 = ax1.annotate('', xy=(.5, .5), xycoords=an2,
  53.                    xytext=(.5, .5), textcoords=an1,
  54.                    ha="center", va="center",
  55.                    bbox=bbox_args,
  56.                    arrowprops=dict(patchA=an1.get_bbox_patch(),
  57.                                    patchB=an2.get_bbox_patch(),
  58.                                    connectionstyle="arc3,rad=0.2",
  59.                                    **arrow_args))
  61. # Finally we'll show off some more complex annotation and placement
  63. text = ax2.annotate('xy=(0, 1)\nxycoords=("data", "axes fraction")',
  64.                     xy=(0, 1), xycoords=("data", 'axes fraction'),
  65.                     xytext=(0, -20), textcoords='offset points',
  66.                     ha="center", va="top",
  67.                     bbox=bbox_args,
  68.                     arrowprops=arrow_args)
  70. ax2.annotate('xy=(0.5, 0)\nxycoords=artist',
  71.              xy=(0.5, 0.), xycoords=text,
  72.              xytext=(0, -20), textcoords='offset points',
  73.              ha="center", va="top",
  74.              bbox=bbox_args,
  75.              arrowprops=arrow_args)
  77. ax2.annotate('xy=(0.8, 0.5)\nxycoords=ax1.transData',
  78.              xy=(0.8, 0.5), xycoords=ax1.transData,
  79.              xytext=(10, 10),
  80.              textcoords=OffsetFrom(ax2.bbox, (0, 0), "points"),
  81.              ha="left", va="bottom",
  82.              bbox=bbox_args,
  83.              arrowprops=arrow_args)
  85. ax2.set(xlim=[-2, 2], ylim=[-2, 2])
  86. plt.show()

注释图示例6

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