如何在 Python 中沿曲线注释文本？

Question

我正在尝试注释图中的文本，以便它们遵循线条的曲率。我有以下情节：

这就是我想要获得的，如果我为注释固定一个特定的 y 值，对于每条曲线，它应该将注释沿着曲线放置在所需的斜率处（即它应该遵循曲线的曲率）为如下图：

没有注释的绘图的可重现代码是：

import numpy as np
import matplotlib.pyplot as plt

x = np.array([[53.4, 57.6, 65.6, 72.9],
            [60.8, 66.5, 73.1, 83.3],
            [72.8, 80.3, 87.2, 99.3],
            [90.2, 99.7, 109.1, 121.9],
            [113.6, 125.6, 139.8, 152]])

y = np.array([[5.7, 6.4, 7.2, 7.8],
            [5.9, 6.5, 7.2, 7.9],
            [6.0, 6.7, 7.3, 8.0],
            [6.3, 7.0, 7.6, 8.2],
            [6.7, 7.5, 8.2, 8.7]])

plt.figure(figsize=(5.15, 5.15))
plt.subplot(111)
for i in range(len(x)):
    plt.plot(x[i, :] ,y[i, :])
plt.xlabel('X')
plt.ylabel('Y')
plt.show()

如何使用 matplotlib 在 Python 中放置此类文本？

Answer 1

抱歉有错别字..（如果有的话） 这是我的答案...这是对@paddyg's 答案的轻微调整，是的，在显示时用鼠标调整图表大小会导致对齐问题。

您将不得不调整偏移量和图表尺寸

输出：

图片 1 有窗口 size(10,5),offset(0,1)

图片 2 有窗口 size(10,5),offset(-4,0)

import matplotlib.pyplot as plt
import math

# I've used 3 plots here:
x_range = [i for i in range(0,101)]
y1_range = [i/1 for i in range(0,101)]
y2_range = [i/2 for i in range(0,101)]
y3_range = [i/3 for i in range(0,101)]

# Size of the ouput figure
x_fig = 10
y_fig = 5
plt.figure(figsize=(x_fig, y_fig))
# The height offset form the midpoint of the line segments
offset = [0,1]

def angle(rng,point,x_fig,y_fig):
    '''
    This will return the alignment angle
    '''
    # print("rng = ", rng)
    x_scale = x_fig /(rng[1] - rng[0])
    y_scale = y_fig /(rng[3] - rng[2])
    assert len(point) == 2, 'point is not properly defined'
    x = point[0]
    y = point[1]
    rot = ((math.atan2( y*y_scale , x*x_scale ))*180)/math.pi
    print(rot,point)
    return rot

def center_point(start,end,height_offset):
    '''
    This will return the location of text placement
    '''
    x_mid = (end[0]-start[0])/2
    y_mid = (end[1]-start[1])/2
    return[x_mid+height_offset[0],y_mid+height_offset[1]]

# Plotting graphs...
plt.plot(x_range,y1_range,color='pink',label = 'y1 - graph')
plt.plot(x_range,y2_range,color='blue',label = 'y2 - graph')
plt.plot(x_range,y3_range,color='red',label =  'y3 - graph')

rng = plt.axis() # This gives the axes range
rot_y1 = angle(rng,[x_range[-1],y1_range[-1]],x_fig,y_fig)
pos_y1 = center_point([x_range[0],y1_range[0]],[x_range[-1],y1_range[-1]],offset)

rot_y2 = angle(rng,[x_range[-1],y2_range[-1]],x_fig,y_fig)
pos_y2 = center_point([x_range[0],y2_range[0]],[x_range[-1],y2_range[-1]],offset)

rot_y3 = angle(rng,[x_range[-1],y3_range[-1]],x_fig,y_fig)
pos_y3 = center_point([x_range[0],y3_range[0]],[x_range[-1],y3_range[-1]],offset)

# Annotating them...(Of course this can be done in a loop as @paddyg's answer suggets.)
plt.annotate('Y1 is here', xy =(0, 0),
                xytext =(pos_y1[0], pos_y1[1]), 
                rotation=rot_y1)
plt.annotate('Y2 is here', xy =(0, 0),
                xytext =(pos_y2[0], pos_y2[1]), 
                rotation=rot_y2)
plt.annotate('Y3 is here', xy =(0, 0),
                xytext =(pos_y3[0], pos_y3[1]),
                rotation=rot_y3)


plt.legend()
plt.xlabel('X - Values')
plt.ylabel('Y - Values')
plt.title('Align the names correctly!')


plt.savefig('demo.png', transparent=True) # Do you want to save a backgroundless .png of the graph?
plt.show()

Answer 2

您可以获取以度为单位的渐变，并在 matplotlib.text.Text 中使用旋转参数

rotn = np.degrees(np.arctan2(y[:,1:]-y[:,:-1], x[:,1:]-x[:,:-1]))

编辑：所以它比我建议的要复杂一些，因为绘图区域被缩放以匹配数据并具有边距等，但你明白了

...
plt.figure(figsize=(7.15, 5.15)) #NB I've changed the x size to check it didn't distort
plt.subplot(111)
for i in range(len(x)):
    plt.plot(x[i, :] ,y[i, :])

rng = plt.axis()
x_scale = 7.15 * 0.78 / (rng[1] - rng[0])         
y_scale = 5.15 * 0.80 / (rng[3] - rng[2])          
rotn = np.degrees(np.arctan2((y[:,1:]-y[:,:-1]) * y_scale,
                              x[:,1:]-x[:,:-1]) * x_scale)
labls = ['first', 'second', 'third', 'fourth', 'fifth']
for i in range(len(x)):
    plt.annotate(labls[i], xy=(x[i,2], y[i,2]), rotation=rotn[i,2])

plt.xlabel('X')

RE-EDIT 注意到缩放错误，但只是巧合！由于缩放，标签的 xy 值也有点近似。