read_icgem_gfc()

Read real spherical harmonic gravity coefficients from an ICGEM formatted file.

Usage

cilm, gm, r0, [errors] = read_icgem_gfc(filename, [errors, lmax, epoch, encoding, quiet)

Returns

cilm : ndarray, size (2, lmax + 1, lmax + 1)

Array of ‘4pi’ normalized spherical harmonic coefficients for the given epoch.

gm : float

Gravitational constant of the model, in m**3/s**2.

r0 : float

Reference radius of the model, in meters.

errors : ndarray, optional, shape (2, lmax + 1, lmax + 1)

Array of the spherical harmonic error coefficients for the given epoch.

Parameters

filename : str or pathlib.Path

The filename containing the spherical harmonic ICGEM-formatted coefficients. filename will be treated as a URL if it starts with ‘http://’, ‘https://’, or ‘ftp://’. If filename ends with ‘.gz’ or ‘.zip’ (or if the path contains ‘/zip/’), the file will be uncompressed before parsing.

errors : str, optional, default = None

Which errors to read. Can be ‘unknown’, ‘calibrated’, ‘formal’ or None.

lmax : int, optional, default = None

Maximum degree to read from the file. If lmax is None, less than 0, or greater than lmax_model, the maximum degree of the model will be used.

epoch : str or float, optional, default = None

The epoch time to calculate time-variable coefficients in YYYYMMDD.DD format. If None then the reference epoch t0 of the model will be used. If the format of the file is ‘icgem2.0’ then the epoch must be specified.

encoding : str, optional, default = None

Encoding of the input file. The default is to use the system default. If the default encoding doesn’t work, try ‘iso-8859-1’.

quiet : bool, default = False

If True, suppress warnings about undefined keywords when reading the file.

Notes

This routine reads ICGEM formatted files of gravitational potential models and outputs arrays of the gravitational potential coefficients, errors, GM, and the reference radius. If epoch is specified, the coefficients will make use of the time variable terms in order to compute and return the potential coefficients for the specified epoch. Otherwise, the coefficients will be returned for the reference epoch of the model.

Valid keys in the header section include: modelname (not used) product_type (only ‘gravity_field’ is allowed) earth_gravity_constant or gravity_constant radius max_degree errors (‘unknown’, ‘formal’, ‘calibrated’ or ‘calibrated_and_formal’) tide_system (not used) norm (not used) format (either None or ‘icgem2.0’)

Valid keys in the data section include: gfc gfct trnd or dot asin acos

Data lines starting with an unknown key are ignored.