Hi John and Martin,
John: Thanks a lot for the information. I put the MSGnavigation properties in the file, and the
projection now fits much better than the vertical perspective projection. Attached you will see a
screenshot of the longitude variable with this projection. At the edges of the globe I still see a
small offset of 0-0.1 degrees, but this is changing more or less where you query.
I tinkered a little bit with the height_from_earth_center and the semi_major and semi_minor axis,
but did not result in a noticable change of the projection. The 2D latitude and longitude fields are
always provided with these files so the projection can be verified with these fields.
> char projection
> projection:proj4_params = "+proj=geos +lon_0=0.000000 +lat_0=0 +h=35807.414063 +a=6378.169 +b=6356.5838" ;
> projection:grid_mapping_name = "MSGnavigation" ;
> projection:longitude_of_projection_origin = 0.f ;
> projection:latitude_of_projection_origin = 0.f ;
> projection:semi_major_axis = 6356584.f ;
> projection:semi_minor_axis = 6378169.f ;
> projection:height_from_earth_center = 4.216397e+07f ;
> projection:scale_x = 35785.83f ;
> projection:scale_y = -35785.83f ;
Martin: I see you started a thread on the cf-satellite and cf-metadata list about a proposition to
add the geos projection to CF. We would be very interested to use this, as this seems to be exactly
the same projection as we use. When formally supported by CF and the tools, we would like to use
this projection info (as you proposed):
> char Projection;
> :grid_mapping_name = "geos";
> :perspective_point_height = 35785831.;
> :semi_major_axis = 6378169.;
> :semi_minor_axis = 6356583.8;
> :latitude_of_projection_origin = 0.;
> :longitude_of_projection_origin = 0.;
Please let me know if you need any support with this. I am willing to generate some testdata and
perform some tests if you like.
Best regards,
Maarten
PS: At KNMI we use the proj4_params attribute, this is not CF standard but is from the ADAGUC data
products standard:
http://adaguc.knmi.nl/contents/documents/ADAGUC_Standard.html. (But we would like
to adhere to the CF standard as much as possible off course).
On 01/24/2012 10:26 AM, Martin Raspaud wrote:
> 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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CF-metadata at cgd.ucar.edu
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--
Maarten Plieger
KNMI, R&D Information and Observation Technology, De Bilt
(t) +31 30 2206330
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Received on Tue Jan 24 2012 - 03:12:55 GMT
