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#107: CF Data Model 1.7 -----------------------------+---------------------------------------------- Reporter: markh | Owner: [email protected] Type: task | Status: new Priority: medium | Milestone: Component: cf-conventions | Version: Resolution: | Keywords: -----------------------------+---------------------------------------------- Comment (by davidhassell): Replying to [comment:17 markh]: Dear Mark, > I have a set of questions regarding the proposed text for [wiki:Ticket107Text9Nov13Transforms transforms] > #70 contains an approved change which will be incorporated into CF1.7 enabling coordinates to be explicitly linked to particular grid_mapping attributes in a file. This facility is not supported by the description of transforms proposed above. It would be useful to know why you think this facility is not supported, as I think that it is. I have editted [wiki:Ticket107Text9Nov13Transforms the description of transforms] to include the first line of the description which didn't make it across from ticket #95, namely: A transform construct defines a mapping from one set of coordinates which can not geo-locate the field construct's data to another set of coordinates that can geo-locate the field construct's data. Here is the CDL example from ticket #70 (multiple grid mappings), with a description of how it would be stored by the proposed Field construct: {{{ double x(x) ; x:standard_name = "projection_x_coordinate" ; double y(y) ; y:standard_name = "projection_y_coordinate" ; double z(z) ; z:standard_name = "height_above_reference_ellipsoid" ; double lat(y, x) ; lat:standard_name = "latitude" ; double lon(y, x) ; lon:standard_name = "longitude" ; float temp(z, y, x) ; temp:standard_name = "air_temperature" ; temp:coordinates = "lat lon" ; temp:grid_mapping = "crsOSGB: x y crsWGS84: lat lon" ; int crsOSGB ; crsOSGB:grid_mapping_name = "transverse_mercator"; crsOSGB:semi_major_axis = 6377563.396 ; crsOSGB:inverse_flattening = 299.3249646 ; crsOSGB:longitude_of_prime_meridian = 0.0 ; crsOSGB:latitude_of_projection_origin = 49.0 ; crsOSGB:longitude_of_central_meridian = -2.0 ; crsOSGB:scale_factor_at_central_meridian = 0.9996012717 ; crsOSGB:false_easting = 400000.0 ; crsOSGB:false_northing = -100000.0 ; crsOSGB:unit = "metre" ; int crsWGS84 ; crsWGS84:grid_mapping_name = "latitude_longitude"; crsWGS84:longitude_of_prime_meridian = 0.0 ; crsWGS84:semi_major_axis = 6378137.0 ; crsWGS84:inverse_flattening = 298.257223563 }}} Field contains: * ''Dimension Coordinates'': x, y * ''Auxiliary Coordinates'': lat, lon * ''Transforms'' : transform_crsOSGB, transform_crsWGS84 where the transforms contain: transform_crsOSGB: * ''NAME'': "transverse_mercator" * ''semi_major_axis'': 6377563.396 * ''inverse_flattening''; 299.3249646 * ''longitude_of_prime_meridian'': 0.0 * ''latitude_of_projection_origin'': 49.0 * ''longitude_of_central_meridian'': -2.0 * ''scale_factor_at_central_meridian'': 0.9996012717 * ''false_easting'': 400000.0 * ''false_northing'': -100000.0 * ''unit'': "metre" * ''INPUT COORDINATES'': x, y transform_crsWGS84: * ''NAME'': "latitude_longitude" * ''longitude_of_prime_meridian'': 0 * ''semi_major_axis'': 6378137.0 * ''inverse_flattening'': 298.257223563 * ''INPUT COORDINATES'': lat, lon So, transform_crsOSGB defines a mapping from coordinates '''x''' and '''y''' to latitude-longitude coordinates on a particularly shaped earth; and transform_crsWGS84 defines a mapping from coordinates '''lat''' and '''lon''' to latitude-longitude coordinates on a different particularly shaped earth. All the best, David -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/107#comment:18> CF Metadata <http://cf-pcmdi.llnl.gov/> CF Metadata This message came from the CF Trac system. To unsubscribe, without unsubscribing to the regular cf-metadata list, send a message to "[email protected]" with "unsubscribe cf-metadata" in the body of your message.
