[CF-metadata] axis attribute

[Richard Gorman]

Dear Jonathon,

This was to interpolate fields onto a lat/lon grid for input to a wave 
model. The interpolation subroutine was written to expect inputs in the 
form of 2D arrays of latitude, longitude and the input field, with 
indices in (x,y) order. So I wanted to identify which were the "x-like" 
and "y-like" dimensions in the original file.

In this case, I suspect it would still work if the "x" and "y" indices 
are transposed, so as long as we can identify the two dimensions which 
are horizontal. But there could be cases where the parity flip would 
matter, e.g. where axial quantities such as vorticity are involved. So I 
think it is useful to allow the axis = X and Y attribute for coordinate 
variables that are a continuous transformation from cartesian 
coordinates or lat/lon coordinates (without a parity inversion).

Regards,
Richard


On 22/11/2006 20:46 p.m., Jonathan Gregory wrote:
> Dear Richard
> 
> ----- Forwarded message from Richard Gorman <r.gorman at niwa.co.nz> -----
>> When I started writing code to handle NetCDF data, the files I was 
>> dealing with used the axis = X and Y attribute for rotated pole 
>> coordinates. So I took that interpretation to be standard and, like you, 
>> coded to use that attribute as one way to identify the spatial 
>> coordinate variables and dimensions.
> 
> What was the importance of identifying them as X and Y? Is it to decide which
> one is the horizontal axis of the plot, for instance?
> 
> Cheers
> 
> Jonathan
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-- 

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Richard Gorman
National Institute of Water and Atmospheric Research
PO Box 11-115, Hamilton, 3251, New Zealand
Tel: +64 7 856 1736 Mob: 021 074 7490 Fax: +64 7 856 0151
Email: r.gorman at niwa.co.nz   Web: http://www.niwa.co.nz
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