Bug summary

When trying to pass levels with unit-ful data to contour, the units are not correctly converted. In the example below I choose 7 contour levels from min(Z) to max(Z), and convert the units from kg to g. This should just change the units, not the locations where contour levels are drawn. The levels array is interpreted without units, and no contours are drawn.

Code for reproduction

import matplotlib.pyplot as plt
import numpy as np

import pint
ureg = pint.UnitRegistry()
ureg.setup_matplotlib()

X, Y = np.meshgrid(np.linspace(-3, 3, 16), np.linspace(-3, 3, 16))
Z = (1 - X/2 + X**5 + Y**3) * np.exp(-X**2 - Y**2)
Z *= ureg.kg
levels = np.linspace(np.min(Z), np.max(Z), 7).to(ureg.g)

fig, ax = plt.subplots()
ax.contour(X, Y, Z, levels=levels)
plt.show()

Actual outcome

Expected outcome

Additional information

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Operating system

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Matplotlib Version

3.7.0.dev1431+g526cb71e20.d20230123

Matplotlib Backend

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Python version

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Jupyter version

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Installation

None