@JimBiardCics The `grid_mapping` attributes were introduced to allow software
to do the transformation if it wanted to, for instance to transform other
locations (apart from the coordinates and boundaries) or do other computations
(such as working out local directions or cell areas). They are
@JonathanGregory Am I right in understanding that back in the day the whole
grid_mapping scheme in CF was added to annotate the relationship between lat
and lon variables (which were always required) and X and Y variables? If the
purpose was annotation and that annotation was itself optional,
Dear @snowman2
That's good about `proj` supporting those two projections. Thanks.
I used `proj` as an example but I was really thinking more about the general
point that Jim raised, about relying on external resources. We've often
discussed this on the former CF email list. I understand from
How are they represented in CF right now? As far as I know only by 2d
coordinates (which doesn't codify the iso-coordinate lines).
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I haven't been following this, but what about tripolar grids, which are often
used in ocean models?
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> Does proj4 include rotated pole and vertical perspective, for instance?
Just to have it noted that it is supported in PROJ (the conversion classes will
be released in pyproj 2.5.0 soon, but the PROJ string version works on all
versions):
```python
>>> from pyproj.crs.coordinate_operation
Dear @JimBiardCics
I appreciate the point and I agree that we should not spend our time doing a
less good job of something which is already available elsewhere. However I
don't think that CF is fairly described as "reinventing the wheel" in this
case. I can suggest a few reasons why we have
Dear @JimBiardCics
Yes, I agree that many projected coordinate systems look somewhat like
east-north, but not all of them, for example stereographic. CF also allows
rotated pole, which is not true east-north by construction, and and indeed any
sort of X and Y grid with 2D lat and lon, such as
