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On 23/01/12 18:40, John Caron wrote:
> On 1/23/2012 10:00 AM, plieger wrote:
>> Dear All,
>>
>>
>> We are struggling with finding the correct CF projection parameters for this data. The data is in
>> satellite view projection, with the current settings we see a slight shift in IDV at the borders of
>> the disc (internally we use proj4_params, which is not a CF standard):
>>
>> char projection ;
>> projection:proj4_params = "+proj=geos +lon_0=0.000000 +lat_0=0 +h=35807.414063 +a=6378.169
>> +b=6356.5838" ;
>> projection:long_name = "Projection information" ;
>> projection:grid_mapping_name = "vertical_perspective" ;
>> projection:latitude_of_projection_origin = 0.000000f ;
>> projection:longitude_of_projection_origin = 0.000000f ;
>> projection:perspective_point_height = 35807416.000000f ;
>> projection:height_above_earth = 35807.414062f ;
>> projection:false_easting = 0.000000f ;
>> projection:false_northing = 0.000000f ;
>> projection:EPSG_code = "none" ;
>>
>> Has anyone a suggestion regarding this issue? When opening these files in IDV you should set the
>> "Data Source Type" to "Image Files (GINI)", otherwise you will have to wait a bit. When you open the
>> variables latitude and longitude you will see that there is a slight shift which increases near the
>> borders.
>>
>> Please let me know what you think!
>>
>> Thanks,
>> Maarten
>>
>
> Hi Martin:
>
> The IDV/CDM code uses a special projection for MSG, because (I think)
> the vertical_perspective is not the exact
> right projection, as you see by the pixels being a bit off.
>
> The MSG projection looks like:
>
> char Projection;
> :*grid_mapping_name* = "MSGnavigation";
> :*longitude_of_projection_origin* = 0.0; // double
> :*latitude_of_projection_origin* = 0.0; // double
> :*semi_major_axis* = 6356755.5; // double
> :*semi_minor_axis* = 6378140.0; // double
> :*height_from_earth_center* = 4.2163970098E7; // double
> :*scale_x* = 35785.830098; // double
> :*scale_y* = -35785.830098; // double
>
>
> details are here:
>
> http://www.unidata.ucar.edu/software/netcdf-java/reference/StandardCoordinateTransforms.html#MSG
>
> The tricky part is to get the projection coordinate x,y values correct.
> The scale_x and scale_y are instrument specific, although Im not sure if
> there
> is more than one instrument.
>
> I kind of made this projection up based on
>
>
> http://www.eumetsat.int/idcplg?IdcService=GET_FILE&dDocName=PDF_CGMS_03&RevisionSelectionMethod=LatestReleased
>
> and code ported from
>
> http://www.eumetsat.int/idcplg?IdcService=GET_FILE&dDocName=zip_tools_msg_nav_c&RevisionSelectionMethod=LatestReleased
>
> Id be happy for some experts to review what Ive done and suggest changes
> if needed.
Hi all,
For information, I pushed a proposal to add the "GEOS" projection to the
CF conventions, so that MSG would be supported.
And as opposed to what is written in the Conventions,
"vertical_perspective" is NOT the MSG native projection.
Best regards,
Martin
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Received on Tue Jan 24 2012 - 02:26:21 GMT
