tight_layout() doesn't work properly on plots with a WCSAxes projection

A Matpltolib Axes created with projection=wcs does not play well with Matplotlib’s tight_layout() method, that is supposed to re-size elements of a figure such that there are no overlapping labels/axes etc.

Consdier the following example:

import matplotlib.pyplot as plt

from astropy.wcs import WCS
from astropy.io import fits
from astropy.utils.data import get_pkg_data_filename

filename = get_pkg_data_filename('galactic_center/gc_msx_e.fits')

hdu = fits.open(filename)[0]
wcs = WCS(hdu.header)

fig = plt.figure(figsize=(8, 6))
n = 2
for i in range(n):
    projection = wcs
    # projection = None
    plt.subplot(n, 1, i + 1, projection=projection)
    # plt.imshow(hdu.data, vmin=-2.e-5, vmax=2.e-4, origin='lower')
    plt.grid(color='white', ls='solid')
    plt.xlabel('Galactic Longitude')
    plt.ylabel('Galactic Latitude')
    plt.title('WCSAxes plot')

fig.tight_layout()
plt.show()

projection=None, no tight_layout: projection=None, with tight_layout: (note how this re-organises things nicely) projection='wcs', no tight_layout: projection='wcs', with tight_layout: Note how things actually get worse!

• astropy 3.1.2
• Matplotlib 3.0.3

[dstansby]

For reference, some simpler code to reproduce this:

import matplotlib.pyplot as plt

from astropy.wcs import WCS
from astropy.io import fits
from astropy.utils.data import get_pkg_data_filename

filename = get_pkg_data_filename('galactic_center/gc_msx_e.fits')

hdu = fits.open(filename)[0]
wcs = WCS(hdu.header)

fig = plt.figure(figsize=(8, 6))
axs = [fig.add_subplot(2, 1, i, projection=wcs) for i in [1, 2]]

fig.tight_layout()
plt.show()

[dstansby]

As I slowly descend into madness trying to work this out, a note that the end goal to get this working is to have TickLabels and AxisLabels have their own get_tight_bbox() methods that can calculate their own Bboxes. This is going to need a lot of refactoring, but I suspect in the long run it should significantly tidy up the WCSAxes code.