Hi Jonathon:
Jonathan Gregory wrote:
>Dear all
>
>This debate went quiet about a month ago. I'd like to propose the following,
>in the light of what was said then.
>
>Requirement: A way to identify the horizontal coordinate variables.
>
>
Sorry I dont understand the requirement. Is this for the case where its
not a lat/lon nor a projection x, y coordinate ? Is the use case
rotated_latitude_longitude ? Are there other use cases?
BTW, theres no reference to how rotated_latitude_longitude works in the
Appendix. Seems to be the only one without furhter explanatoin.
>(NB coordinate variables means 1D, in the Unidata sense, as usual in CF.)
>
>Proposal: It can be done using COARDS rules for units in the case of latitude
>and longitude. In other cases (such as projection coordinates, rotated latitude
>and longitude) the standard name can be used, but that requires recognising
>specific names, and standard names are optional anyway. The axis attribute is
>also optional but if present it can be used to identify horizontal coordinates
>as those having axis="X" or axis="Y". If both X- and Y-axis are identified,
>X-Y-up should define a right-handed coordinate system i.e. rotation from the
>positive X direction to the positive Y direction is anticlockwise if viewed
>from above. The axis attribute is allowed for longitude (X) and latitude (Y)
>coordinate variables. The axis attribute is not allowed for auxiliary
>coordinate variables. Auxiliary coordinate variables can be identified as
>lying in the horizontal surface (e.g. 2D latitude and longitude) by the fact
>of their having dimensions which all belong to 1D horizontal coordinate
>variables.
>
>
>Change to current standard: Remove the prohibition on axis attribute for
>rotated lat and lon. Introduce the requirement for X-Y-up to be right-handed.
>Add a remark about how aux coord vars can be inferred to be horizontal. Make
>it clear that axis is not allowed on aux coord vars (but that is probably
>already the case, so not a change to the standard).
>
>Cheers
>
>Jonathan
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>
Received on Wed Dec 27 2006 - 20:47:11 GMT
