Hi.
I think there is still value in adding an attribute to the grid_mapping set where the name of the vertical datum can be supplied. The datums (data?) have ?standard? names (not CF standard names). If you aren?t using a named vertical datum, you could specify either ?none? (or just don?t specify the attribute) or ?custom? if you are using a datum that hasn?t been given a name. I agree that the name alone is not necessarily sufficient, but it does provide a human-readable marker, whereas the WKT and URN approaches require further digging.
Just to be clear, I?m not advocating either/or with regards to the more rigorous approaches. A ?vertical_datum? attribute that contains a human-readable name should be present in addition to one (or more) of the other approaches.
Grace and peace,
Jim
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On Feb 7, 2014, at 10:25 AM, Hedley, Mark <mark.hedley at metoffice.gov.uk> wrote:
> Hello Rich
>
> I think that using the WKT representation for vertical datum definitions is a good approach
>
> As you have indicated, it is to be supported in CF 1.7 and provides a controlled terminology set for this purpose.
>
> There is an example using the OS Newlyn datum in the draft spec which fits quite nicely.
>
> I'd rather see us adopting WKT for complex issues like this than creating a syntax for encoding CF grid_mapping attributes, there's a lot of prior art we can benefit from.
>
> For example WKT enables me to specify more than just the EPSG code, which is useful as not all datum instances are provided by EPSG
>
> mark
> ________________________________________
> From: CF-metadata [cf-metadata-bounces at cgd.ucar.edu] on behalf of Signell, Richard [rsignell at usgs.gov]
> Sent: 04 February 2014 11:47
> To: CF metadata
> Subject: [CF-metadata] Vertical datums (again)
>
> CF folks,
>
> On a telecon yesterday with a coastal inundation modeling group, one
> of the PIs asked me how to handle vertical datums in NetCDF --
> specifically where to specify that the model bathymetry and water
> levels were were relative to NAVD88. I wasn't sure how to reply.
>
> Was there any resolution to the 2nd half of this question asked back in 2011?
> http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2011/054483.html
>
> I looked at the draft 1.7 spec, and the only vertical datum reference
> info I found was the ability to specify VERT_DATUM in the new CRS
> well-known-text (WKT) section:
> http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.7-draft1/ch05s06.html#idp5644304
>
> Is this how we should specify the vertical datum in CF, using VERT_DATUM in WKT?
>
> Thanks,
> Rich
> --
> Dr. Richard P. Signell (508) 457-2229
> USGS, 384 Woods Hole Rd.
> Woods Hole, MA 02543-1598
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Received on Fri Feb 07 2014 - 08:38:23 GMT
