[gdal-dev] NetCDF generated by GDAL not compliant with CF-1.0 for geographical grids

[Frank Warmerdam]

Reinoud Bokhorst wrote:
> Hi,
> I have a WCS that reads and writes NetCDF using GDAL. The source NetCDF has a regular lat/lon geographical grid (no projection). The NetCDF that is generated following a WCS request (parameters: BBOX=0.0,55.0,5.0,60.0&SRS=epsg:4326&RESX=0.5&RESY=0.5) has the following header (ncdump -c):
> 
> netcdf my_netcdf {
> dimensions:
>         x = 10 ;
>         y = 10 ;
> variables:
>         char GDAL_Geographics ;
>                 GDAL_Geographics:Northernmost_Northing = 55. ;
>                 GDAL_Geographics:Southernmost_Northing = 60. ;
>                 GDAL_Geographics:Easternmost_Easting = 5. ;
>                 GDAL_Geographics:Westernmost_Easting = 0. ;
>                 GDAL_Geographics:spatial_ref = "GEOGCS[\"WGS
> 84\",DATUM[\"WGS_1984\",SPHEROID[\"WGS
> 84\",6378137,298.257223563,AUTHORITY[\"EPSG\",\"7030\"]],TOWGS84[0,0,0,0,0,0,0],AUTHORITY[\"EPSG\",\"6326\"]],PRIMEM[\"Greenwich\",0,AUTHORITY[\"EPSG\",\"8901\"]],UNIT[\"degree\",0.01745329251994328,AUTHORITY[\"EPSG\",\"9122\"]],AUTHORITY[\"EPSG\",\"4326\"]]"
> ;
>                 GDAL_Geographics:GeoTransform = "0 0.5 -0 55 0 0.5 " ;
>                 GDAL_Geographics:grid_mapping_name = "Geographics
> Coordinate System" ;
>                 GDAL_Geographics:long_name = "Grid_latitude" ;
>         float Band1(y, x) ;
>                 Band1:_FillValue = 0.f ;
>                 Band1:grid_mapping = "GDAL_Geographics" ;
>                 Band1:long_name = "GDAL Band Number 1" ;
> 
> // global attributes:
>                 :Conventions = "CF-1.0" ;
> data:
> }
> 
> 
> However, it seems that the grid_mapping_name "Geographics Coordinate System" is not a valid grid_mapping_name in the CF-1.0 convention (only 8 are mentioned in the convention). In CF-1.0 a geographic grid should be represented like this:
> 
> 
> netcdf my_netcdf_cf1.0 {
> dimensions:
>         y = 10 ;
>         x = 10 ;
> variables:
>         float y(y) ;
>                 y:standard_name = "latitude" ;
>                 y:units = "degrees_north" ;
>         float x(x) ;
>                 x:standard_name = "longitude" ;
>                 x:units = "degrees_east" ;
>         float Band1(y, x) ;
>                 Band1:_FillValue = 0.f ;
>                 Band1:long_name = "GDAL Band Number 1" ;
> 
> // global attributes:
>                 :Conventions = "CF-1.0" ;
> data:
> 
>  y = 55, 55.5, 56, 56.5, 57, 57.5, 58, 58.5, 59, 59.5 ;
> 
>  x = 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 ;
> }
> 
> 
> Where only the 'units' attribute is required to indicate lat / lon. I am not sure if in this case the y and x arrays should start at 55.0N and 5.0E respectively or at 55.25N and 5.25E.

Reinoud,

I would encourage you to file this as a ticket.  Unfortunately the netcdf
driver is not currently being well maintained so I don't know if/when the
problem will be addressed.



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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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