Support inset_axes zooms for all GeoAxes projections

Description

inset_axes doesn’t work for geographic plots.

Steps to reproduce

import proplot as plot

f, axs = plot.subplots(
    ncols=2, axwidth=2.5,
    proj='robin', proj_kw={'lon_0': 180}
)
axs.format(
    suptitle='Figure with single projection',
    coast=True, latlines=30, lonlines=60
)

axi = axs.inset(
    [0, 0, 10, 10], transform='data', zoom=True,
    zoom_kw={'color': 'red3', 'lw': 2}
)

Error

Traceback (most recent call last):
  File "test_del.py", line 16, in <module>
    zoom_kw={'color': 'red3', 'lw': 2}
  File "/yin_raid/xin/miniconda3/envs/python37/lib/python3.7/site-packages/proplot/subplots.py", line 217, in _iterator
    ret.append(func(*args, **kwargs))
  File "/yin_raid/xin/miniconda3/envs/python37/lib/python3.7/site-packages/proplot/axes.py", line 1334, in inset_axes
    bb = locator(None, None)
  File "/yin_raid/xin/miniconda3/envs/python37/lib/python3.7/site-packages/proplot/axes.py", line 348, in inset_locator
    bb = mtransforms.TransformedBbox(bbox, trans)
  File "/yin_raid/xin/miniconda3/envs/python37/lib/python3.7/site-packages/matplotlib/transforms.py", line 1005, in __init__
    raise ValueError("'transform' must be an instance of "
ValueError: 'transform' must be an instance of 'matplotlib.transform.Transform'

Proplot version

0.5.0

[lukelbd]

This is actually not an advertised feature but it’s on my to-do list under the category “make XYAxes features work with rectangular projections like Mercator and Plate Carrée”. See #131 for details.

Will leave this issue open as a feature request for now. As a workaround you can probably make your own inset axes using the default cartopy API with e.g.

import cartopy.crs as ccrs
ax = fig.add_axes([x0, x1, y0, y1], projection=ccrs.PlateCarree())
ax.set_extent([lon0, lon1, lat0, lat1])
<plotting_code_here>

[lukelbd]

This seems to work pretty well for Plate Carree projections in the latest version. Have to set manually set the left/bottom spaces or else the result is wrong… but not too much effort.

import proplot as pplt
import cartopy.crs as ccrs
pplt.rc.reso = 'med'
fig, axs = pplt.subplots(
    proj='pcarree', coast=True, tight=True, bottom=7, left=1
)
fig.format(lonlim=(0, 180), latlim=(0, 90))
axs.scatter(120, 30)
bounds = (0.8, -0.6, 0.8, 0.8)
iax = axs.inset(bounds, proj='pcarree', zoom=True, zoom_kw={'ec': 'red', 'lw': 2})
iax.format(coast=True, rivers=True, lonlim=(100, 130), latlim=(15, 40))
fig.show()

Non-Plate Carree are a different story thought. Again matplotlib isn’t supplying the correct bounds:

import proplot as pplt
import cartopy.crs as ccrs

pplt.rc.reso = 'med'
fig, axs = pplt.subplots(
    proj='robin', coast=True, tight=True, bottom=7, left=1
)
fig.format(lonlim=(0, 180), latlim=(0, 90))
axs.scatter(120, 30)
bounds = (0.8, -0.6, 0.8, 0.8)
iax = axs.inset(bounds, proj='pcarree', zoom=True, zoom_kw={'ec': 'red', 'lw': 2})
iax.format(coast=True, rivers=True, lonlim=(100, 130), latlim=(15, 40))

Since the issue with using the wrong “transform” is fixed I’ll remove the “bug” tag.