The association of X and Y with latitude and longitude is a complicated and
difficult topic. Here's a good article about the issue.
https://wiki.osgeo.org/wiki/Axis_Order_Confusion
Here's a summary and recap as I see it.
Geodesy uses a left-hand mathematical coordinate system so that the
@snowman2 I don't think we can make that assumption, at least not in your
example and as you've expressed it. There is no direct connection in your
example between the lats and lons and the Xs and Ys. The connection of X with
projection_x_coordinate and Y with projection_y_coordinate is pretty
For horizontal coordinates, the CF `axis` attribute should be used to indicate
which axis is `X` and which `Y`, where `X` is "like" longitude and `Y` "like"
latitude. This correspondence can't really be more than a rough guide, for
reasons mentioned above. Doesn't the `axis` attribute meet the
As far as the temporal axis goes, CF is quite strongly "future positive". It
would take a lot of work to change this. I expect that the paleoclimate people
would appreciate the ability to do "past positive" time coordinates that would
use a (currently non-existent) calendar appropriate to their
@snowman2 I am generally opposed to this proposal as it stands.
If we want to adopt some sort of convention about this sort of thing, I suggest
it be something like what I've written below.
For spatial coordinate systems, add an attribute named "fluffy" (this is a
placeholder name — I'm unable
Adding excerpt from: http://docs.opengeospatial.org/is/12-063r5/12-063r5.html#35
```
Axis direction indicates the positive increment along an axis. The handedness
of a 2- or 3-dimensional coordinate system may be derived from the directions.
Requirement: the following constraints shall apply:
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
@snowman2 There is a long-standing use of the units 'degrees_north' and
'degrees_east' within CF that I think precludes making a change to using units
of 'degrees' for latitude and longitude. It is used by some as a way to
determine that a given variable is a latitude or longitude coordinate
@JonathanGregory Most all projected coordinate systems are east-north aligned.
The main questions are which component is which and which direction is
positive. But your question points out the more difficult case of swath data
where X and Y are not aligned to east and north.
--
You are
