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- CF standard: add a dummy variable crs and add all grid mapping related meta-data as attributes.
- proposed extension: make sure that the dummy variable crs it an integer and that its value is the EPSG code of the coordinate system, e.g:
- 28992 for Dutch Rijksdriehoek (projection_x_coordinate,projection_y_coordinate)
- 4326 for WGS84 global ellipsoid (latitude, longitude)
- 32631 for WGS 84 / UTM zone 31N (projection_x_coordinate,projection_y_coordinate)
- proposed extension: add a WKT (well-known text) string of all grid mapping related meta-data (the WKT quite laborious for parsing though).
Examples
UNSTRUC map file on local xy-grid (e.g., Amersfoort / RD New).
- Currently lacks lon/lat for x/y-grids.
- The RD projection (oblique stereographic) is not recognized in CF-1.4 (and many others), in PROJ.4 'sterea' is used: http://www.spatialreference.org/ref/epsg/28992/
- More details are here: unstructured grid format.
netcdf test_map { // Only relevant parts for crs are shown! dimensions: nNetCell = 665 ; time = UNLIMITED ; // (1 currently) variables: double time(time) ; time:units = "seconds since 2010-01-01 00:00:00" ; double NetCell_xc(nNetCell) ; NetCell_xc:units = "m" ; NetCell_xc:standard_name = "projection_x_coordinate" ; NetCell_xc:long_name = "Net cell circumcenter x" ; NetCell_xc:bounds = "NetCellContour_x" ; double NetCell_yc(nNetCell) ; NetCell_yc:units = "m" ; NetCell_yc:standard_name = "projection_y_coordinate" ; NetCell_yc:long_name = "Net cell circumcenter y" ; NetCell_yc:bounds = "NetCellContour_y" ; double s1(time, nNetCell) ; s1:cell_methods = "area: mean" ; s1:coordinates = "NetCell_xc Netcell_yc" ; s1:grid_mapping = "crs" ; int crs ; crs:grid_mapping_name = "oblique_stereographic" ; crs:projection_name = "Amersfoort / RD New" ; crs:semi_major_axis = 6377397.f ; crs:inverse_flattening = 299.1528f ; crs:latitude_of_projection_origin = 52.15616f ; crs:longitude_of_central_meridian = 5.387639f ; crs:scale_factor_at_projection_origin = 0.9999079f ; crs:false_easting = 155000 ; crs:false_northing = 463000 ; //... crs = 28992 ;
UNSTRUC map file on lon/lat-grid (e.g., WGS 1984)
- More details are here: unstructured grid format.
netcdf test_map { // Only relevant parts for crs are shown! dimensions: nNetCell = 184324 ; time = UNLIMITED ; // (1 currently) variables: double time(time) ; time:units = "seconds since 2010-01-01 00:00:00" ; double NetCell_xc(nNetCell) ; NetCell_xc:units = "degrees_east" ; NetCell_xc:standard_name = "longitude" ; NetCell_xc:long_name = "Net cell circumcenter x" ; NetCell_xc:bounds = "NetCellContour_x" ; double NetCell_yc(nNetCell) ; NetCell_yc:units = "degrees_north" ; NetCell_yc:standard_name = "latitude" ; NetCell_yc:long_name = "Net cell circumcenter y" ; NetCell_yc:bounds = "NetCellContour_y" ; double s1(time, nNetCell) ; s1:cell_methods = "area: mean" ; s1:coordinates = "NetCell_xc Netcell_yc" ; s1:grid_mapping = "crs" ; int crs ; crs:grid_mapping_name = "latitude_longitude" ; crs:longitude_of_prime_meridian = 0.f ; crs:semi_major_axis = 6378137.f ; crs:inverse_flattening = 298.2572f ; //... crs = 4326 ;
