具有相同头部长度的 Python 注释箭头 [英] Python annotation arrows with same headlength

问题描述

我正在使用 matplotlib 创建带箭头的注释.

I'm using matplotlib to create annotations with arrows.

from matplotlib import pyplot as plt
plt.figure()
plt.annotate('Text1', xy=(1, 0), xytext=(1, 1), arrowprops=dict(alpha=0.5, fc='r', ec='r', headwidth=10))
plt.annotate('Text2', xy=(3, 0), xytext=(3, 3), arrowprops=dict(alpha=0.5, fc='r', ec='r', headwidth=10))
plt.annotate('Text3', xy=(6, 0), xytext=(6, 6), arrowprops=dict(alpha=0.5, fc='r', ec='r', headwidth=10))
plt.annotate('Text4', xy=(9, 0), xytext=(9, 9), arrowprops=dict(alpha=0.5, fc='r', ec='r', headwidth=10))
plt.xlim((0, 10))
plt.ylim(0, 10)
plt.show()

可以看出，箭头的长度受线长的影响，并且在箭头之间有所不同.

As can be seen, the length of the arrow heads is affected by the line-length and varies between the arrows.

我正在寻找一种方法来创建具有不同线长但相同箭头长度的箭头.尽管注释手册页上列出了许多选项，但我无法产生所需的结果.

I'm looking for a way to create arrows with different line-lengths but equal arrow-headlengths. Although many options are listed on the annotations manual page, i was not able to produce the desired result.

作为替代方法，我尝试使用 plt.arrow 单独绘制箭头.在那种情况下，箭头看起来像预期的那样，但是当使用透明度时，额外的线条变得可见.

As an alternative approach i tried to plot the arrows seperatedely using plt.arrow. In that case the arrow heads looked as desired, but when using transparency, additional lines became visible.

最好的问候，zinjaai

Best regards, zinjaai

推荐答案

在 arrowprops 中你不能指定头部的长度，但是 frac 论证指定头部的长度作为箭头长度的分数.由于您知道 xy 和 xytext，您可以计算所需头部长度的必要分数.

In the arrowprops you can't specify the length of the head, but the frac arguement specifies the length of the head as a fraction the arrow length. Since you know xy and xytext you can compute the necessary fraction for a desired headlength.

对于您提供的示例(头部长度为 0.5)，我没有很快完成.

I've don't it quickly for the example you provided (with an head length of 0.5).

from matplotlib import pyplot as plt
plt.figure()
plt.annotate('Text1', xy=(1, 0), xytext=(1, 1), 
        arrowprops=dict(alpha=0.5, fc='r', ec='r', headwidth=10, frac=0.5/1))
plt.annotate('Text2', xy=(3, 0), xytext=(3, 3), 
        arrowprops=dict(alpha=0.5, fc='r', ec='r', headwidth=10, frac=0.5/3))
plt.annotate('Text3', xy=(6, 0), xytext=(6, 6), 
        arrowprops=dict(alpha=0.5, fc='r', ec='r', headwidth=10, frac=0.5/6))
plt.annotate('Text4', xy=(9, 0), xytext=(9, 9), 
        arrowprops=dict(alpha=0.5, fc='r', ec='r', headwidth=10, frac=0.5/9))
plt.xlim((0, 10))
plt.ylim(0, 10)
plt.show()

结果:

您可以将其包装在一个函数中，该函数计算箭头的长度(给定 xy 和 xytext)，然后将其传递给 plt.annotate.

You could wrap this in a function, which computes the length of the arrow (given xy and xytext) and then passes that on to plt.annotate.

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