Module frametransform 

Conversion between coordinate frames Coordinate Frame Transformations

This module provides quaternion-based rotations between reference frames used in satellite astrodynamics.

Available Transforms

Function	From	To	Accuracy	Notes
[qitrf2gcrf]	ITRF	GCRF	Full IERS 2010	Computationally expensive; requires EOP
[qgcrf2itrf]	GCRF	ITRF	Full IERS 2010	Conjugate of qitrf2gcrf
[qitrf2gcrf_approx]	ITRF	GCRF	~1 arcsec	IAU-76/FK5 approximation; fast
[qgcrf2itrf_approx]	GCRF	ITRF	~1 arcsec	Conjugate of qitrf2gcrf_approx
[qteme2itrf]	TEME	ITRF	Exact	For SGP4 output; Vallado Eq. 3-90
[qteme2gcrf]	TEME	GCRF	~1 arcsec	Composes TEME→ITRF via qitrf2gcrf_approx
[qmod2gcrf]	MOD	GCRF	Full	Vallado Eqs. 3-88, 3-89
[qtirs2cirs]	TIRS	CIRS	Full	Earth rotation angle only

Frame Descriptions

• GCRF (Geocentric Celestial Reference Frame): Inertial frame, IERS 2010
• ITRF (International Terrestrial Reference Frame): Earth-fixed frame
• TEME (True Equator Mean Equinox): Frame used by SGP4 propagator
• TIRS (Terrestrial Intermediate Reference System): IERS 2010 intermediate frame
• CIRS (Celestial Intermediate Reference System): IERS 2010 intermediate frame
• MOD (Mean of Date): Precession-only frame

Functions

earth_rotation_angle

Earth Rotation Angle

eqeq

Equation of Equinoxes Equation of the equinoxes

from_gcrf

Unified rotation builder: return the DCM that transforms a 3-vector from GCRF into frame at the current state.

gast

Greenwich Apparent Sidereal Time

gcrf_to_itrf_state

Transform a satellite state (position and velocity) from GCRF (inertial) to ITRF (Earth-fixed, rotating) at a given time.

gcrf_to_itrf_state_approx

Approximate version of gcrf_to_itrf_state using the IAU-76/FK5 reduction (accurate to ~1 arcsec for position). Inverse of itrf_to_gcrf_state_approx; sweep term subtracted in ITRF (polar motion neglected).

gcrf_to_lvlh

Compute the GCRF-to-LVLH rotation matrix. Transpose of lvlh_to_gcrf.

gcrf_to_ntw

Compute the GCRF-to-NTW rotation matrix. Transpose of ntw_to_gcrf.

gcrf_to_ric

Backward-compatibility alias for gcrf_to_rtn. See ric_to_gcrf for rationale.

gcrf_to_rtn

Compute the GCRF-to-RTN rotation matrix from position and velocity.

gmst

Greenwich Mean Sidereal Time

itrf_to_gcrf_state

Transform a satellite state (position and velocity) from ITRF (Earth-fixed, rotating) to GCRF (inertial) at a given time.

itrf_to_gcrf_state_approx

Approximate version of itrf_to_gcrf_state using the IAU-76/FK5 reduction (accurate to ~1 arcsec for position).

lvlh_to_gcrf

Compute the LVLH-to-GCRF rotation matrix from position and velocity.

ntw_to_gcrf

Compute the NTW-to-GCRF rotation matrix from position and velocity.

qcirs2gcrs

Return quaternion representing rotation from the CIRS (Celestial Intermediate Reference System) to the GCRS (Geocentric Celestial Reference Frame) at given instant

qcirs2gcrs_dxdy

qgcrf2itrf

Quaternion representing rotation from the Geocentric Celestial Reference Frame (GCRF) to the International Terrestrial Reference Frame (ITRF)

qgcrf2itrf_approx

Approximate rotation from Geocentric Celestial Reference Frame to International Terrestrial Reference Frame

qitrf2gcrf

Quaternion representing rotation from the International Terrestrial Reference Frame (ITRF) to the Geocentric Celestial Reference Frame (GCRF)

qitrf2gcrf_approx

Approximate rotation from International Terrestrial Reference Frame to Geocentric Celestial Reference Frame

qitrf2tirs

Rotation from International Terrestrial Reference Frame (ITRF) to the Terrestrial Intermediate Reference System (TIRS)

qmod2gcrf

Rotate from Mean Equinox of Date (MOD) coordinate frame to Geocentric Celestial Reference Frame

qteme2gcrf

Rotation from True Equator Mean Equinox (TEME) frame to Geocentric Celestial Reference Frame (GCRF)

qteme2itrf

Rotation from True Equator Mean Equinox (TEME) frame to International Terrestrial Reference Frame (ITRF)

qtirs2cirs

Quaternion representing rotation from the Terrestrial Intermediate Reference System to the Celestial Intermediate Reference System

qtod2mod_approx

Approximate rotation from True of Date to Mean of Date coordinate frame

ric_to_gcrf

Backward-compatibility alias for rtn_to_gcrf. The ric_to_gcrf name was the canonical spelling in earlier satkit versions; new code should use rtn_to_gcrf (which matches the CCSDS OEM/OMM convention), but this alias is kept so existing Rust callers don’t break.

rtn_to_gcrf

Compute the RTN-to-GCRF rotation matrix from position and velocity.

to_gcrf

Unified rotation builder: return the DCM that transforms a 3-vector from frame into GCRF at the current state.