pyrfu.pyrf.cotrans#

pyrfu.pyrf.cotrans(inp, flag, hapgood: bool = True)[source]#

Coordinate transformation GE0/GEI/GSE/GSM/SM/MAG as described in [1]

Parameters:

  • inp (xarray.DataArray) – Time series of the input field.

  • flag (str) – Coordinates transformation “{coord1}>{coord2}”, where coord1 and coord2 can be geo/gei/gse/gsm/sm/mag (case-insensitive). If only “{coord2}” is given, coord1 is read from the COORDINATE_SYSTEM attribute of inp. “dipoledirectiongse” returns the dipole direction in GSE at the times of inp.

  • hapgood (bool, Optional) – Indicator if original Hapgood sources should be used for angle computations or if updated USNO-AA sources should be used. Default = true, meaning original Hapgood sources.

Returns:

out – Time series of the field in coord2. If inp is a scalar time series, the transformation matrices.

Return type:

xarray.DataArray

Raises:

ValueError – If the input frame is neither in flag nor in the COORDINATE_SYSTEM attribute of inp, if they differ, or if the transformation is unknown.

Notes

With hapgood=False, the Greenwich mean sidereal time is computed from UT, as the USNO formula requires. irfu-matlab computes it from TT, which rotates GEO by 0.29 deg about the z-axis, so the transformations between GEO or MAG and GEI, GSE, GSM or SM differ from irfu-matlab by up to 0.29 deg. The dipole direction (used for GSM and SM) is always computed with the Hapgood sidereal time.

Examples

>>> from pyrfu.mms import get_data
>>> from pyrfu.pyrf import cotrans

Time interval

>>> tint = ["2019-09-14T07:54:00.000", "2019-09-14T08:11:00.000"]

Spacecraft index

>>> mms_id = 1

Load magnetic field in GSE coordinates

>>> b_gse = get_data("b_gse_fgm_srvy_l2", tint, mms_id)

Transform to GSM assuming that the original coordinates system is part of the inp metadata

>>> b_gsm = cotrans(b_gse, 'GSM')

If the original coordinates is not in the meta

>>> b_gsm = cotrans(b_gse, 'GSE>GSM')

Compute the dipole direction in GSE

>>> dipole = cotrans(b_gse.time, 'dipoledirectiongse')

References

[1]

Hapgood 1997 (corrected version of Hapgood 1992) Planet.Space Sci..Vol. 40, No. 5. pp. 71l - 717, 1992