如何在 matplotlib 中用沿线旋转的文本注释线

Question

我想在两点之间添加一个注释，文本在中间，然后旋转文本以与直线对齐。当前示例未按预期旋转：

import matplotlib.pyplot as plt
import numpy as np

def ann_distance(ax,xyfrom,xyto,text=None):
    midx = (xyto[0]+xyfrom[0])/2
    midy = (xyto[1]+xyfrom[1])/2
    if text is None:
        text = str(np.sqrt( (xyfrom[0]-xyto[0])**2 + (xyfrom[1]-xyto[1])**2 ))

    ax.annotate("",xyfrom,xyto,arrowprops=dict(arrowstyle='<->'))
    p1 = ax.transData.transform_point((xyfrom[0], xyfrom[1]))
    p2 = ax.transData.transform_point((xyto[0], xyto[1]))
    rotn = np.degrees(np.arctan2(p2[1]-p1[1], p2[0]-p1[0]))
    ax.text(midx,midy,text,ha='center', va='bottom',rotation=rotn,fontsize=16)
    return

x = np.linspace(0,2*np.pi,100)

width = 800
height = 600

fig, ax = plt.subplots()
ax.plot(x,np.sin(x))
ann_distance(plt.gca(),[np.pi/2,1],[2*np.pi,0],'$sample$')
plt.show()

当前输出：

Answer 1

添加两个 text 参数使文本旋转与行匹配：

transform_rotates_text=True 相对于图形比例旋转文本
rotation_mode='anchor' anchors the rotation relative to va and ha

dx = xyto[0] - xyfrom[0]
dy = xyto[1] - xyfrom[1]
rotn = np.degrees(np.arctan2(dy, dx)) # not the transformed p2 and p1

ax.text(midx, midy, text, ha='center', va='bottom', fontsize=16,
        rotation=rotn, rotation_mode='anchor', transform_rotates_text=True)

如何在 matplotlib 中用沿线旋转的文本注释线

How to annotate line with text rotated along the line in matplotlib

python

matplotlib