On Mon, Jul 30, 2012 at 10:56 PM, Kennedy, Paul <[email protected]> wrote:
> Tim,
> I could not agree more. Indeed, I would go even further and permit a simple
> EPSG code as a suitable definition of the geodesy. EPSG:4326 is all you need
> to specify WGS ellipsoid, datum etc.
>
> crs:epsg_code = 4326 ; //this would be the 99% case. This is how google
> openlayers, wms, google, bing and others handle the tricky subject of geodesy
> metadata.
Unfortunately, the majority of CF community does not agree with the
use of codes because they are not "self-describable". Have a look at
the archives of this mailing list and you will see a load of threads
on this subject.
If you want EPSG:4326, there are parameters that describe it (see the
link you submitted)
In fact, it is quite compact in CF notation (see example 5/9 of the
CF-1.6 document)
int crs ;
crs:grid_mapping_name = "latitude_longitude";
crs:longitude_of_prime_meridian = 0.0 ;
crs:semi_major_axis = 6378137.0 ;
crs:inverse_flattening = 298.257223563 ;
>
> WKT is also very handy, but harder to generate and parse. I suspect this is
> the 1% case.
Thus the need to write the necessary CF parameters to describe WGS84.
This is easier than parsing WKT.
Etienne
>
> http://spatialreference.org/ref/epsg/4326/
>
>
> regards
>
> Paul Kennedy
> Technical Development Manager
> Fugro Survey Pty Ltd
> 24 Geddes St, Balcatta
> Western Australia 6021
> ABN: 81 009 172 990
> Ph : +61 (0)8 6477 4400
> Direct: +61 (0)8 6477 4418
> Fax : +61 (0)8 6477 4499
> Mobile: +61 (0)439 518 265
> Email : [email protected]
> Skype : p.kennedy.fugro.com
>
>
>
> -----Original Message-----
> From: CF-metadata [mailto:[email protected]] On Behalf Of
> Timothy Hume
> Sent: Tuesday, 31 July 2012 9:34 AM
> To: [email protected]
> Subject: Re: [CF-metadata] How to include EPSG codes or WKT information in a
> CF file [SEC=UNCLASSIFIED]
>
> Hi Jonathan,
>
> Thanks for the help. I can see that option 80 is probably better, but option
> 69 is a lot easier for software developers to bolt onto existing NetCDF
> files. Most of the people I talk to don't see why anyone is interested in
> anything other than latitudes and longitudes on a spherical Earth; all the
> stuff about shape of the Earth etc is irrelevant to their needs. The truth
> is, because most of the NWP data I use is on a rather coarse grid, the grid
> mapping information is not that important; two coordinate variables with the
> longitudes and latitudes is sufficient for most purposes.
>
> Therefore, the path of least resistance is option 69 (with all its potential
> pit falls); I think option 80 will be too much, and a lot of data writers
> will simply decide to add no grid mapping information at all, a worse
> situation than option 69.
>
> Cheers,
>
> Tim Hume
> Bureau of Meteorology
> ________________________________________
> From: CF-metadata [[email protected]] On Behalf Of Jonathan
> Gregory [[email protected]]
> Sent: Monday, 30 July 2012 7:10 PM
> To: [email protected]
> Subject: [CF-metadata] How to include EPSG codes or WKT information in a CF
> file [SEC=UNCLASSIFIED]
>
> Dear Tim
>
> There are two open CF trac tickets that relate to this issue, proposing to
> add new conventions to store OGC information in different ways in CF. Ticket
> 80 https://cf-pcmdi.llnl.gov/trac/ticket/80 proposes several new attributes
> which correspond to WKT elements that currently do not have grid_mapping
> equivalents. Ticket 69 https://cf-pcmdi.llnl.gov/trac/ticket/69 proposed to
> add an attribute to record the WKT information without translation.
> Personally I prefer the former because I am concerned about duplication and
> possible inconsistency of information, but please have a look at the tickets
> and form your own view, and add comments if you like. So the answer to your
> question is that there is not yet a CF standard way to do it, but there will
> be.
>
> Best wishes
>
> Jonathan
>
>
> ----- Forwarded message from Timothy Hume <[email protected]> -----
>
>> Date: Mon, 30 Jul 2012 11:36:19 +1000
>> From: Timothy Hume <[email protected]>
>> To: "[email protected]" <[email protected]>
>> Subject: [CF-metadata] How to include EPSG codes or WKT information in a CF
>> file [SEC=UNCLASSIFIED]
>>
>> Hi,
>>
>> I am adding grid mapping information to my NetCDF files. My data are on a
>> lon-lat grid on a spherical Earth. I can put in the standard CF attributes,
>> grid_mapping_name etc, but also want to include the EPSG and WKT codes to
>> help software applications that might want these. I have not been able to
>> find out how this is done in NetCDF-CF, so am using this format:
>> =
>> int crs ;
>> crs:grid_mapping_name = "latitude_longitude" ;
>> crs:earth_radius = 6371007.0 ;
>> crs:prime_meridian = 0.0 ;
>> crs:epsg_code = 4047 ;
>> crs:wkt = "GEOGCS[\"Unspecified datum based upon the
>> GRS 1980 Authalic Sphere\",DATUM[\"Not_specified_based_on
>> _GRS_1980_Authalic_Sphere\",SPHEROID[\"GRS 1980 Authalic
>> Sphere\",6371007,0,AUTHORITY[\"EPSG\",\"7048\"]],AUTHORITY[\"EPSG\",\
>> "6047\"]],PRIMEM[\"Greenwich\",0,AUTHORITY[\"EPSG\",\"8901\"]],UNIT[\"
>> degree\",0.01745329251994328,AUTHORITY[\"EPSG\",\"9122\"]],AUTHORITY[\
>> "EPSG\",\"4047\"]]" ;
>>
>> What do other people do when including this extra grid information?
>>
>> Cheers,
>>
>> Tim Hume
>> Centre for Australian Weather and Climate Research Bureau of
>> Meteorology Melbourne Australia
>> _______________________________________________
>> CF-metadata mailing list
>> [email protected]
>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>
> ----- End forwarded message -----
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