[CF-metadata] identification of vector components
mark.hedley at metoffice.gov.uk
Thu Apr 5 10:35:08 MDT 2012
There is a statement in the definition of many standard names which are used for vector component definitions, e.g.:
"x" indicates a vector component along the grid x-axis, when this is not true longitude, positive with increasing x. Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the atmosphere has the standard name upward_air_velocity.)
I think that the statement 'when this is not true longitude' is problematic, particularly for software converting from other formats, where x indicates the grid i direction, independent of rotation or projection. I do not think it is the place for standard_name to limit the use of the term 'x' to cases where the horizontal coordinate reference system is not 'true latitude longitude'
I propose that these terms be removed from all standard names which have 'x' or 'y' as a modifier.
This would enable all x-ward and y-ward definitions to be used, independent of the grid_mapping, as standard names.
eastward and northward remain useful modifiers as many models may choose to output eastward vector components where east is not the x direction for the model grid.
The work on vector containers in:
has indicated a good way forward for identifying vector components, and identifying that vectors are with respect to a grid_mapping. I think this proposed change would interface nicely to the proposal in ticket 79
How would this proposal be viewed by the community?
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