s1etad.geometry module

Tools for geometry management and coordinate conversion.

class s1etad.geometry.GridGeocoding(grid_latitude, grid_longitude, grid_height=0, xaxis=None, yaxis=None, ellipsoid_name='WGS84', interpolation_kind='cubic')

Bases: object

Class to perform backward and forward geocoding using grid data.

This class implements a simple geocoding method that exploits pre-computed grids of latitude, longitude and height values.

The method is not as accurate as solving the range-Doppler equations.

Parameters:

• grid_latitude (ndarray) – regular grid of latitudes (in degrees) of shape [Ny, Nx] (y:azimuth and x:range)

• grid_longitude (ndarray) –

  regular grid of longitudes (in degrees) of shape [Ny, Nx]

  (y:azimuth and x:range)

• grid_height (ndarray) – regular grid of heights of shape [Ny, Nx] (y:azimuth and x:range)

• xaxis (ndarray) – axis in the x dimension (range) for the grids. It could be the range time. If not provided then default is np.arange(Nx)

• yaxis (ndarray) – axis in the y dimension (azimuth) for the grids. It could be the azimuth time (elapsed seconds since a reference). If not provided then default is np.arange(Ny)

• ellipsoid_name (str) – the identifier of the standard ellipsoid to be used for coordinate conversion. Default: “WGS84”

• interpolation_kind (str) – Default: “cubic”

backward_geocode(lats, lons, heights=0, deg=True)

Perform the back geocoding: (lat, lon, h) -> (x, y).

Important

The current implementation always returns the solution of the backward geocoding at the height corresponding to the reference surface included in the ETAD product (provides latitude longitude and h grids), which is computed using the Copernicus DEM 90m.

Parameters:

• lats (list or ndarray) – array [N] of latitude for which the back geocoding is requested

• lons (list or ndarray) – array [N] of longitude for which the back geocoding is requested

• heights (float, list or ndarray) –

  height for which the back geocoding is requested.

  Warning

  this parameter is not used in the current implementation.

• deg (bool) – True if input geodetic coordinates are expressed in degrees, False otherwise

Returns:

x0:

array [N] of x coordinates (or range time) for each input in lats, lons, heights

y0:

array [N] of y coordinates (or azimuth time) for each input in lats, lons, heights

Return type:

ndarray, ndarray

forward_geocode(x, y, deg=True)

Perform forward geocoding (x, y) -> (lat, lon, h).

This is simply obtained by re-interpolating the latitude, longitude and height grids at the desired coordinates.

Parameters:

• x (list or ndarray) – x coordinate or range time at which the geocoding is performed

• y (list or ndarray) – y coordinate or azimuth time at which the geocoding is performed

• deg (bool) – if True than the output lat and lon are expressed in degrees, otherwise in radians

Returns:

latitude:

array [N] of latitudes for each input coordinate

longitude:

array [N] of longitudes for each input coordinate

height:

array [N] of heights for each input coordinate

Return type:

ndarray, ndarray, ndarray

height(x, y)

Interpolate the height grid at the (x, y) coordinates.

Parameters:

• x (ndarray) – array [N] of x coordinates (or range time) for each input in the latitude_grid. x shall be the same quantity as used for initialization (coordinates or time).

• y (ndarray) – array [N] of y coordinates (or azimuth time) for each input in the latitude_grid. y shall be the same quantity as used for initialization (coordinates or time).

Returns:

interpolated height

Return type:

ndarray

latitude(x, y)

Interpolate the latitude grid at the (x, y) coordinates.

Parameters:

• x (ndarray) – array [N] of x coordinates (or range time) for each input in the latitude_grid. x shall be the same quantity as used for initialization (coordinates or time).

• y (ndarray) – array [N] of y coordinates (or azimuth time) for each input in the latitude_grid. y shall be the same quantity as used for initialization (coordinates or time).

Returns:

interpolated latitude ([deg])

Return type:

ndarray

longitude(x, y)

Interpolate the longitude grid at the (x, y) coordinates.

Parameters:

• x (ndarray) – array [N] of x coordinates (or range time) for each input in the latitude_grid. x shall be the same quantity as used for initialization (coordinates or time).

• y (ndarray) – array [N] of y coordinates (or azimuth time) for each input in the latitude_grid. y shall be the same quantity as used for initialization (coordinates or time).

Returns:

interpolated longitude ([deg])

Return type:

ndarray

s1etad.geometry.ecef_to_geodetic(x, y, z, ell='WGS84', deg=True)

Convert ECEF coordinates into geodetic.

s1etad.geometry.geodetic_to_ecef(lat, lon, h, ell='WGS84', deg=True)

Convert geodetic coordinates into ECEF.