Method
NumCosmoHaloPositionpolar_angles
Declaration [src]
void
nc_halo_position_polar_angles (
NcHaloPosition* hp,
gdouble ra,
gdouble dec,
gdouble* theta,
gdouble* phi
)
Description [src]
Computes the spherical coordinates of a sky position in a halo-centered coordinate system. The coordinate system is obtained by a rigid rotation of the celestial sphere that places the halo at the north pole.
The returned polar angle theta is the angular separation between the halo and the
sky position. The azimuth phi is measured in the rotated coordinate system.
The rotation preserves all angular distances and relative position angles on the
sky. Its orientation is uniquely fixed by requiring that the halo is first brought
into the xz-plane and then rotated onto the positive z-axis, with no additional
rotation about the halo axis. Consequently, phi is uniquely defined and is
consistent for all sky positions associated with the same halo.
Because the input positions are right ascension and declination, phi is the
position angle in the celestial convention ($\phi_C$, increasing eastward). A
consumer that expresses ellipticities in a different handedness (see
NcWLEllipticityFrame) must convert it accordingly, e.g. with nc_wl_ellipticity_celestial_to_frame_angle().