Don't assume arcseconds when CUNIT metadata isn't present

Raise a more sensible Attribute error if CUNIT metadata not present

Fix mapbase tests

Only set LASCO cunit if present

Fix maps doctests

Add changelog

Fix map_from_numpy_array

Fix maps_example

Add clearer error message when unit meatadata not present

Assume arcseconds for EIT maps

Update error message

Move cunit check to _validate_metadata

Revert change to LASCOmap

changelog/2847.breaking.rst

@@ -0,0 +1,2 @@
+Maps no longer assume that the pixel units are arcseconds if the units aren't
+explicitly set.

docs/guide/data_types/maps.rst

@@ -45,7 +45,7 @@ given then some default values are assumed. Here is a simple example::
     >>> import numpy as np
 
     >>> data = np.arange(0,100).reshape(10,10)
-    >>> header = {'cdelt1': 10, 'cdelt2': 10, 'telescop':'sunpy'}
+    >>> header = {'cdelt1': 10, 'cdelt2': 10, 'telescop':'sunpy', 'cunit1': 'arcsec', 'cunit2': 'arcsec'}
     >>> my_map = sunpy.map.Map(data, header)
 
 The keys in the header follows the `FITS standard <https://fits.gsfc.nasa.gov/fits_dictionary.html>`_.

examples/map/map_from_numpy_array.py

@@ -19,7 +19,7 @@
 # SunPy Maps store 2D data in a numpy array and additional data in a metadata
 # dictionary giving information relating to the data and instrument.
 data = np.random.rand(20,15)
-header = {}
+header = {'cunit1': 'arcsec', 'cunit2': 'arcsec'}
 manual_map = sunpy.map.Map((data, header))
 
 ##############################################################################

examples/map/maps_example.py

@@ -27,7 +27,7 @@
 # Or using creating manually by using tuple with the data/header within:
 
 data = np.random.rand(20, 15)
-header = {}
+header = {'cunit1': 'arcsec', 'cunit2': 'arcsec'}
 manual_map = sunpy.map.Map((data, header))
 
 ##############################################################################

sunpy/map/mapbase.py

@@ -679,8 +679,8 @@ def spatial_units(self):
         """
         Image coordinate units along the x and y axes (i.e. cunit1, cunit2).
         """
-        return SpatialPair(u.Unit(self.meta.get('cunit1', 'arcsec')),
-                           u.Unit(self.meta.get('cunit2', 'arcsec')))
+        return SpatialPair(u.Unit(self.meta.get('cunit1')),
+                           u.Unit(self.meta.get('cunit2')))
 
     @property
     def rotation_matrix(self):
@@ -773,8 +773,17 @@ def _validate_meta(self):
             CUNIT1, CUNIT2, WAVEUNIT
 
         """
+        msg = ('Image coordinate units for axis {} not present in metadata. '
+               'It can be set using `map.meta["cunit{}"] = unit`.')
+        err_message = []
+        for i in [1, 2]:
+            if self.meta.get(f'cunit{i}') is None:
+                err_message.append(msg.format(i, i))
 
-        for meta_property in ('cunit1', 'cunit2', 'waveunit'):
+        if err_message:
+            raise AttributeError('\n'.join(err_message))
+
+        for meta_property in ('waveunit'):
             if (self.meta.get(meta_property) and
                 u.Unit(self.meta.get(meta_property),
                        parse_strict='silent').physical_type == 'unknown'):

sunpy/map/sources/soho.py

@@ -65,6 +65,8 @@ def __init__(self, data, header, **kwargs):
         # Fill in some missing info
         self.meta['detector'] = "EIT"
         self.meta['waveunit'] = "Angstrom"
+        self.meta['cunit1'] = self.meta.get('cunit1', 'arcsec')
+        self.meta['cunit2'] = self.meta.get('cunit2', 'arcsec')
         self._fix_dsun()
         self._nickname = self.detector
         self.plot_settings['cmap'] = plt.get_cmap(self._get_cmap_name())

sunpy/map/tests/test_mapbase.py

@@ -223,7 +223,9 @@ def test_rotation_matrix_cd_cdelt():
         'CD2_1': 10,
         'CD2_2': 0,
         'NAXIS1': 6,
-        'NAXIS2': 6
+        'NAXIS2': 6,
+        'CUNIT1': 'arcsec',
+        'CUNIT2': 'arcsec'
     }
     cd_map = sunpy.map.Map((data, header))
     np.testing.assert_allclose(cd_map.rotation_matrix, np.array([[0., -1.], [1., 0]]))
@@ -243,7 +245,9 @@ def test_rotation_matrix_cd_cdelt_square():
         'CD2_1': 10,
         'CD2_2': 0,
         'NAXIS1': 6,
-        'NAXIS2': 6
+        'NAXIS2': 6,
+        'CUNIT1': 'arcsec',
+        'CUNIT2': 'arcsec'
     }
     cd_map = sunpy.map.Map((data, header))
     np.testing.assert_allclose(cd_map.rotation_matrix, np.array([[0., -1], [1., 0]]))
@@ -669,6 +673,8 @@ def test_missing_metadata_warnings():
     # Checks that warnings for missing metadata are only raised once
     with pytest.warns(Warning) as record:
         array_map = sunpy.map.Map(np.random.rand(20, 15), {})
+        array_map.meta['cunit1'] = 'arcsec'
+        array_map.meta['cunit2'] = 'arcsec'
         array_map.peek()
     # There should be 4 warnings for missing metadata
     assert len([w for w in record if 'Missing metadata' in str(w)]) == 4