Read spherical harmonic coefficients from an ICGEM GFC ascii-formatted file.

This function only reads files with the gravity field spherical harmonic coefficients.

## Usage

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

## Returns

cilm : array
Array with the coefficients with the shape (2, lmax + 1, lmax + 1) for the given epoch.
gm : float
Standard gravitational constant of the model, in m3/s2.
r0 : float
Reference radius of the model, in meters.
errors : array, optional
Array with the errors of the coefficients with the shape (2, lmax + 1, lmax + 1) for the given epoch.

## Parameters

filename : str
The ascii-formatted filename containing the spherical harmonic coefficients.
errors : str, optional
Which errors to read. Can be either “calibrated”, “formal” oNone. Default is None.
lmax : int, optional
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
The epoch time to calculate time-variable coefficients in YYYYMMDD.DD format. If None then reference epoch t0 of the model will be used. If format of the file is ‘icgem2.0’ then epoch must be specified.
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