How to comment text on curved lines in Python?

Question

I am trying to comment on the text in the graphs so that they follow the curvature of the line. I have the following plot:

And this is what I want to get, if I fix a specific y value for the annotation, for each curve it should place the annotation along the curve at the required slope (i.e. it should follow the curvature of the curve), since below:

Reproducible code for a graph without annotations:

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() 

How to post such texts in Python using matplotlib?

Answer 1

You can get the gradient in degrees and use it in matplotlib.text.Text with argument rotate

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

EDIT: so this is a little messy than I expected, since the plot area is scaled to fit the data and has fields, etc., but you get the idea

 ... 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 noticed that the scaling was wrong, but it just happened to work by coincidence! Also, the xy values ​​of the labels are a little closer due to scaling.