Regression: imshow on geo axes produces an empty plot in matplotlib 2.0.0

[lpsinger]

Bug summary

In Matplotlib 1.5.3, it was possible to use imshow on geo axes (e.g. the mollweide projection defined in matplotlib.projections.geo. In Matplotlib 2.0.0, this produces a blank plot.

Code for reproduction

Here is an example that worked in 1.5.3.

from matplotlib import pyplot as plt
import numpy as np

lon = np.linspace(-np.pi, np.pi)
lat = np.linspace(-np.pi/2, np.pi/2)
lon, lat = np.meshgrid(lon, lat)

ax = plt.axes(projection='mollweide')
ax.grid()
ax.imshow(lon, extent=[-np.pi, np.pi, -np.pi/2, np.pi/2], aspect=ax.get_aspect())
plt.savefig('test.png')

Actual outcome

This is the output on Matplotlib 2.0.0: blank axes.

Expected outcome

This was the output in Matplotlib 1.5.3.

Matplotlib version

Installed from MacPorts on OS X 10.11.6 "El Capitan". Port versions:

• py27-matplotlib @1.5.3_0+cairo
• py27-matplotlib @2.0.0_0+cairo

[efiring]

It appears that in 1.5.3 the image was being created in Cartesian coordinates and then clipped to the projection. Is this what you want?

[lpsinger]

Yes.

[efiring]

That seems like fundamentally incorrect behavior, doesn't it? Wouldn't most users expect that if anything, imshow with a projection would warp the image to that projection? It's never done that, though. In 2.0 its behavior with a log scale on one or both axes has changed so that it does map the image to the scale, but I think that its behavior with a non-affine projection has always been undefined. If so, it should raise an error. Alternatively, I suppose it could warn and drop back to the 1.5.x behavior. Comments, @mdboom?

[lpsinger]

I was looking through past PRs... did this change occur in #5718?

[WeatherGod]

yes, that is the rework that Eric is referring to.

…

On Mon, Jan 23, 2017 at 5:04 PM, Leo Singer ***@***.***> wrote: I was looking through past PRs... did this change occur in #5718 <#5718>? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#7903 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AARy-F-GjvXUZW3O-sXcDqGT0iE0cRvwks5rVSPRgaJpZM4Lp_U0> .

[lpsinger]

Oh, OK! I modified my test code to use ax.imshow(..., extent=[0, 1, 0, 1], transform=ax.transAxes):

#!/usr/bin/env python
from matplotlib import pyplot as plt
import numpy as np

lon = np.linspace(-np.pi, np.pi)
lat = np.linspace(-np.pi/2, np.pi/2)
lon, lat = np.meshgrid(lon, lat)

ax = plt.axes(projection='mollweide')
ax.grid()
ax.imshow(lon, extent=[0, 1, 0, 1], aspect=ax.get_aspect(), transform=ax.transAxes)
plt.savefig('test.png')

And it works now:

[lpsinger]

Oh, OK! I modified my test code to use ax.imshow(..., extent=[0, 1, 0, 1], transform=ax.transAxes):

Was this just a latent bug in my own code that was revealed by the transition to 2.0.0? If so, then we can close this issue.