Update dimensions metadata when resampling a map

[wtbarnes]

Currently, after resampling a map, the naxis1 and naxis2 entries in the metadata, which hold the dimension of each axis, are not updated. See the resample method in sunpy/map/mapbase.py.

This should be just a matter of adding two lines in the update metadata section of the resample method.

See example below

Map from sample data. Note that the metadata gives the x and y dimensions as 1024 and that it gives the same output as the dimensions property.

>>> import sunpy.map                                                         
>>> import sunpy.data.sample                                                 
>>> aia_test_map = sunpy.map.Map(sunpy.data.sample.AIA_171_IMAGE)
>>> aia_test_map.dimensions
... Pair(x=<Quantity 1024.0 pix>, y=<Quantity 1024.0 pix>)            
>>> aia_test_map.meta['naxis1']
... 1024
>>> aia_test_map.meta['naxis2']
... 1024

Now resample the map to 100-by-100 pixels

>>> import astropy.units as u
>>> aia_test_map_resampled = aia_test_map.resample([100,100]*u.pixel)
>>> aia_test_map_resampled.dimensions
... Pair(x=<Quantity 100.0 pix>, y=<Quantity 100.0 pix>)
>>> aia_test_map_resampled.meta['naxis1']
... 1024
>>> aia_test_map_resampled.meta['naxis2']
... 1024

So after resampling, the metadata remains unchanged though the dimensions are updated with the resampling.

Though maybe the original resolution of the map should be preserved in the metadata.

[wtbarnes]

Given that the general consensus (for now at least) is that we don't want to much with header keywords, I'm going to close this very old issue.