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.
Attached is a GRIB file that the CDM seems to get right. If you look at
it in ToolsUI (a debugging tool for the CDM/IDV code base) you can
examine the coordinates (CoordSys tab)
and see a nice picture (Feature Types /Grid - click on the red alien
button twice) .
ToolsUI webstart link:
http://www.unidata.ucar.edu/software/netcdf-java/v4.2/webstart/netCDFtools.jnlp
You might try copying the coordinates from the GRIB file ans see if they
work on your data.
John
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Received on Mon Jan 23 2012 - 10:40:26 GMT
