How to plot in figure coordinates in matplotlib?

Question

I want to retrieve the figure coordinates of one scatter point and set a second point exactly at that point - solely based on figure coordinates and not on axes or data coordinates.

My approach, to plot the red cross (last line) on top of the blue point, does not work yet:

import matplotlib.pyplot as plt
fig, ax0 = plt.subplots()

point0 = ax0.scatter(1, 1)
ax0.set_xlim(0, 2)
ax0.set_ylim(0, 2)

bbox = ax0.get_position()
ax1 = fig.add_axes(bbox)

ax1.set_xlim(0, 2)
ax1.set_ylim(0, 2)
ax1.axis('off')

point1 = ax1.scatter(1, 0.5, marker='x')

x, y = ax0.transData.transform((1, 1))
print('x={}'.format(x), 'y={}'.format(y))
ax1.scatter(x, y, marker='x', color='r', transform=fig.transFigure)

prints: x=221.4 y=144.72

I would be thankful for any hints how to solve this.

Answer 1

It turns out that transformation operations solve this problem:

import matplotlib.pyplot as plt
fig, ax0 = plt.subplots()

point0 = ax0.scatter(1, 1)
bbox = ax0.get_position()
ax0.set_xlim(0, 2)
ax0.set_ylim(0, 2)
mytrans = ax0.transData + ax0.transAxes.inverted()
x, y = mytrans.transform((1, 1))

ax1 = fig.add_axes(bbox)
ax1.axis('off')
ax1.set_xlim(0, 2)
ax1.set_ylim(0, 2)

print('x={}'.format(x), 'y={}'.format(y))
ax1.scatter(x, y, marker='x', color='r', transform=ax1.transAxes)

The point needs to be transformed from data to axes coordinates.