unifhy.BritishNationalGrid.from_field

classmethod BritishNationalGrid.from_field(field)

Instantiate a BritishNationalGrid from spatial dimension coordinates of a cf.Field.

Parameters

field: cf.Field

The field object that will be used to instantiate a BritishNationalGrid instance. This field must feature a ‘projection_y_coordinate’ and a ‘projection_x_coordinate’ dimension coordinates, and these must feature bounds. In addition, the coordination conversion ‘transverse_mercator’ must correspond to the parameters of the British National Grid (EPSG:27700).

Returns

BritishNationalGrid

Examples

Instantiating from a 2D field:

>>> import cf
>>> import numpy
>>> f = cf.Field()
>>> yc = f.set_construct(
...     cf.DimensionCoordinate(
...         properties={'standard_name': 'projection_y_coordinate',
...                     'units': 'metres',
...                     'axis': 'Y'},
...         data=cf.Data([12500, 13500, 14500]),
...         bounds=cf.Bounds(
...             data=cf.Data(
...                 numpy.column_stack(
...                     (numpy.arange(12000, 15000, 1000),
...                      numpy.arange(13000, 16000, 1000))
...                 )
...             )
...         )
...     ),
...     axes=f.set_construct(cf.DomainAxis(size=3))
... )
>>> xc = f.set_construct(
...     cf.DimensionCoordinate(
...         properties={'standard_name': 'projection_x_coordinate',
...                     'units': 'metres',
...                     'axis': 'X'},
...         data=cf.Data([80500, 81500, 82500, 83500]),
...         bounds=cf.Bounds(
...             data=cf.Data(
...                 numpy.column_stack(
...                     (numpy.arange(80000, 84000, 1000),
...                      numpy.arange(81000, 85000, 1000))
...                 )
...             )
...         )
...     ),
...     axes=f.set_construct(cf.DomainAxis(size=4))
... )
>>> crs = f.set_construct(
...     cf.CoordinateReference(
...         coordinate_conversion=cf.CoordinateConversion(
...             parameters={'grid_mapping_name': 'transverse_mercator',
...                         'projected_crs_name': 'OSGB 1936 / British National Grid',
...                         '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_conversion_factor': 0.0174532925199433}
...         ),
...         datum=cf.Datum(
...             parameters={'geographic_crs_name': 'OSGB 1936',
...                         'horizontal_datum_name': 'OSGB_1936',
...                         'semi_major_axis': 6377563.396,
...                         'inverse_flattening': 299.3249646,
...                         'towgs84': [375., -111., 431., 0., 0., 0., 0.],
...                         'longitude_of_prime_meridian': 0.0}
...         ),
...         coordinates=(yc, xc)
...     )
... )
>>> sd = BritishNationalGrid.from_field(f)
>>> print(sd)
BritishNationalGrid(
    shape {Y, X}: (3, 4)
    Y, projection_y_coordinate (3,): [12500, 13500, 14500] m
    X, projection_x_coordinate (4,): [80500, ..., 83500] m
    Y_bounds (3, 2): [[12000, ..., 15000]] m
    X_bounds (4, 2): [[80000, ..., 84000]] m
)

Using the field interface back and forth:

>>> sd1 = BritishNationalGrid.from_extent_and_resolution(
...     projection_y_coordinate_extent=(12000, 15000),
...     projection_x_coordinate_extent=(80000, 84000),
...     projection_y_coordinate_resolution=1000,
...     projection_x_coordinate_resolution=1000,
... )
>>> sd2 = BritishNationalGrid.from_field(sd1.to_field())
>>> sd2 == sd1
True