Matplotlib - rotating text on log scale where angles are incorrectly rounded

Question

I am trying to have text rotate onto a plot which is shown on log scale. When I compute the angles (based on the solution in this answer) the angles are getting incorrec

Answer 1

I updated the solution to the original question with a class RotationAwareAnnotation2, which will be better suited here. It would first transform the points into screen coordinates, and then apply the rotation.

This this case it would look as follows.

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.text as mtext
import matplotlib.transforms as mtransforms


class RotationAwareAnnotation2(mtext.Annotation):
    def __init__(self, s, xy, p, pa=None, ax=None, **kwargs):
        self.ax = ax or plt.gca()
        self.p = p
        if not pa:
            self.pa = xy
        kwargs.update(rotation_mode=kwargs.get("rotation_mode", "anchor"))
        mtext.Annotation.__init__(self, s, xy, **kwargs)
        self.set_transform(mtransforms.IdentityTransform())
        if 'clip_on' in kwargs:
            self.set_clip_path(self.ax.patch)
        self.ax._add_text(self)

    def calc_angle(self):
        p = self.ax.transData.transform_point(self.p)
        pa = self.ax.transData.transform_point(self.pa)
        ang = np.arctan2(p[1]-pa[1], p[0]-pa[0])
        return np.rad2deg(ang)

    def _get_rotation(self):
        return self.calc_angle()

    def _set_rotation(self, rotation):
        pass

    _rotation = property(_get_rotation, _set_rotation)


x = np.linspace(0, 20, 100)
f = lambda x: np.exp(x**2)
y = f(x)

fig, ax = plt.subplots()
ax.plot(x, y)
ax.set(yscale = 'log', ylim=(1e0, 1e180), xlim=(-1, 20), xlabel=r'$x$')

annots= []
for xi in [0,2,4,7,18]:
    an = RotationAwareAnnotation2("A", xy=(xi,f(xi)), p=(xi+.01,f(xi+.01)), ax=ax,
                                  xytext=(-1,1), textcoords="offset points", 
                                  ha="center", va="baseline", fontsize=40)
    annots.append(an)

ax.set_title(r'$\exp(x^2)$', y=1.05)
fig.savefig('logscale.pdf', format='pdf', bbox_inches='tight')

plt.show()