I noticed that the positioning of pyplot.arrow (white) is odd.
I misused pyplot.quiver (black) as reference:
import numpy as np
import matplotlib.pyplot as plt
Z = np.random.random((50,50))
fig, ax = plt.subplots(figsize=(5.9,5.9))
im = ax.imshow(Z, origin='lower', cmap='coolwarm')
ax.hlines( 10 , 0, Z.shape[0]-1, color='black', ls='-', lw=1, alpha=.3)
ax.hlines( 40 , 0, Z.shape[0]-1, color='black', ls='-', lw=1, alpha=.3)
ax.arrow( 10, 10, 0, 30, color='white', head_width=1, length_includes_head=True)
ax.quiver(20, 10, 0, 30, angles='xy', scale_units='xy', scale=1)
ax.grid(visible=False)
fig.savefig('arrows.jpg', dpi=300)
The head overshoots considerably ...
... and the tail is actually off as well.
Am I doing something wrong or is there a way to fix this?