native_lon_lat_from_ra_dec¶
- rubin_sim.utils.native_lon_lat_from_ra_dec(ra, dec, obs_metadata)¶
Convert the RA and Dec of a star into `native’ longitude and latitude.
Native longitude and latitude are defined as what RA and Dec would be if the celestial pole were at the location where the telescope is pointing. The coordinate basis axes for this system is achieved by taking the true coordinate basis axes and rotating them once about the z axis and once about the x axis (or, by rotating the vector pointing to the RA and Dec being transformed once about the x axis and once about the z axis). These are the Euler rotations referred to in Section 2.3 of
Calabretta and Greisen (2002), A&A 395, p. 1077
Note: RA, and Dec are assumed to be in the International Celestial Reference System. Before calculating native longitude and latitude, this method will convert RA and Dec to observed geocentric coordinates.
WARNING: This method does not account for apparent motion due to parallax. This method is only useful for mapping positions on a theoretical celestial sphere.
@param [in] ra is the RA of the star being transformed in degrees (in the International Celestial Reference System)
@param [in] dec is the Dec of the star being transformed in degrees (in the International Celestial Reference System)
@param [in] obs_metadata is an ObservationMetaData characterizing the pointing of the telescope.
@param [out] lonOut is the native longitude in degrees
@param [out] latOut is the native latitude in degrees