Here is an example of a lon/lat definition (no PROJCS) with TOWGS84
EPSG code 4618 (SAD69 datum used in South America)
OGC WKT :
GEOGCS["SAD69",
DATUM["South_American_Datum_1969",
SPHEROID["GRS 1967 Modified",6378160,298.25,
AUTHORITY["EPSG","7050"]],
TOWGS84[-57,1,-41,0,0,0,0],
AUTHORITY["EPSG","6618"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4618"]]
or in simple form (no authority nodes):
GEOGCS["SAD69",
DATUM["South_American_Datum_1969",
SPHEROID["GRS 1967 Modified",6378160,298.25],
TOWGS84[-57,1,-41,0,0,0,0]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433]]
and PROJ.4 string:
'+proj=longlat +ellps=aust_SA +towgs84=-57,1,-41,0,0,0,0 +no_defs '
cheers Etienne
On Mon, Nov 21, 2011 at 6:24 PM, Etienne Tourigny
<etourigny.dev at gmail.com> wrote:
> Here is an example of a projection (modis sinusoidal) that is not
> supported by CF:
>
> PROJCS["unnamed",
> ? ?GEOGCS["Unknown datum based upon the custom spheroid",
> ? ? ? ?DATUM["Not_specified_based_on_custom_spheroid",
> ? ? ? ? ? ?SPHEROID["Custom spheroid",6371007.181,0]],
> ? ? ? ?PRIMEM["Greenwich",0],
> ? ? ? ?UNIT["degree",0.0174532925199433]],
> ? ?PROJECTION["Sinusoidal"],
> ? ?PARAMETER["longitude_of_center",0],
> ? ?PARAMETER["false_easting",0],
> ? ?PARAMETER["false_northing",0],
> ? ?UNIT["metre",1,
> ? ? ? ?AUTHORITY["EPSG","9001"]]]
>
> Using GDAL's netcdf driver (dev version) to convert a gtiff file with
> this projection to netcdf, the associated CF grid_mapping is
>
> ? ? ? ?char sinusoidal ;
> ? ? ? ? ? ? ? ?sinusoidal:grid_mapping_name = "sinusoidal" ;
> ? ? ? ? ? ? ? ?sinusoidal:longitude_of_prime_meridian = 0. ;
> ? ? ? ? ? ? ? ?sinusoidal:semi_major_axis = 6371007.181 ;
> ? ? ? ? ? ? ? ?sinusoidal:inverse_flattening = 0. ;
> ? ? ? ? ? ? ? ?sinusoidal:false_easting = 0. ;
> ? ? ? ? ? ? ? ?sinusoidal:false_northing = 0. ;
> ? ? ? ? ? ? ? ?sinusoidal:longitude_of_central_meridian = 0. ;
> ? ? ? ? ? ? ? ?sinusoidal:spatial_ref = "PROJCS[\"unnamed\",GEOGCS[\"Unknown datum
> based upon the custom
> spheroid\",DATUM[\"Not_specified_based_on_custom_spheroid\",SPHEROID[\"Custom
> spheroid\",6371007.181,0]],PRIMEM[\"Greenwich\",0],UNIT[\"degree\",0.0174532925199433]],PROJECTION[\"Sinusoidal\"],PARAMETER[\"longitude_of_center\",0],PARAMETER[\"false_easting\",0],PARAMETER[\"false_northing\",0],UNIT[\"metre\",1,AUTHORITY[\"EPSG\",\"9001\"]]]"
> ;
> ? ? ? ? ? ? ? ?sinusoidal:GeoTransform = "-7783653.63766700029 463.312716527500015
> 0 1111950.51966700004 0 -463.312716527500015 " ;
>
> The last 2 attributes (spatial_ref and GeoTransform) are used by
> GDAL's netcdf driver because the CF standard does not support it
> (yet).
>
> As you can see, the only thing that is not CF is the sinusoidal
> grid_mapping_name
>
>
> On Mon, Nov 21, 2011 at 11:37 AM, Jonathan Gregory
> <j.m.gregory at reading.ac.uk> wrote:
>> Dear all
>>
>> Several people contributed to an email thread in October about OGC CRS WKT.
>> It would help the discussion about how to include WKT, or the ideas it
>> embodies, in CF if we had some more concrete examples of coordinate systems
>> that people would like to use in CF but can't currently be represented in CF,
>> and how they are described in WKT. If you can post any to this email thread,
>> that would be much appreciated.
>>
>> Also, anyone is welcome to contribute to trac ticket 69, as below, where we are
>> discussing this.
>> https://cf-pcmdi.llnl.gov/trac/ticket/69
>> To contribute, you need a CF trac account. Please email
>> webmaster at pcmdi.llnl.gov
>> to request one if you don't have one.
>>
>> Best wishes and thanks
>>
>> Jonathan
>>
>>
>> ----- Forwarded message from Jonathan Gregory <j.m.gregory at reading.ac.uk> -----
>>
>>> Date: Wed, 9 Nov 2011 09:56:01 +0000
>>> From: Jonathan Gregory <j.m.gregory at reading.ac.uk>
>>> To: cf-metadata at cgd.ucar.edu
>>> Subject: Fwd: Re: [CF-metadata] Question on WKT representation of CRS
>>>
>>> Dear all
>>>
>>> It would be very helpful if those who are familiar with OGC CRS WKT - several
>>> people contributed to this email thread in October - could contribute to the
>>> discussion in trac ticket 69. In this ticket, Phil Bentley has proposed a new
>>> attribute to allow WKT to be recorded in CF metadata. I am grateful to Phil
>>> for making the proposal, but I am concerned about our adopting this proposal
>>> because of possible inconsistency with other CF metadata. I have described
>>> some specific concerns in the ticket, and asked what specific requirements
>>> there are i.e. more use cases, because I think it is necessary to understand
>>> the implications of what we put in the CF standard. Unfortunately I don't know
>>> much about how the parts of the coordinate reference system are defined, but
>>> other people who read this email list must do, I am sure! If anyone can add
>>> further information and viewpoints to the discussion, it would help.
>>>
>>> Best wishes and thanks
>>>
>>> Jonathan
>>
>> ----- End forwarded message -----
>> _______________________________________________
>> CF-metadata mailing list
>> CF-metadata at cgd.ucar.edu
>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>
>
Received on Mon Nov 21 2011 - 13:32:26 GMT
