normal_triad#
- pygaia.astrometry.vectorastrometry.normal_triad(phi, theta)#
Calculate the so-called normal triad [p, q, r] associated with a spherical coordinate system. The three vectors are:
p - The unit tangent vector in the direction of increasing longitudinal angle phi. q - The unit tangent vector in the direction of increasing latitudinal angle theta. r - The unit vector toward the point (phi, theta).
- Parameters:
phi (float or array) – Longitude-like angle (e.g., right ascension, ecliptic longitude) in radians
theta (float or array) – Latitide-like angle (e.g., declination, ecliptic latitude) in radians
- Returns:
p, q, r – The normal triad as the vectors p, q, r as (N,3) arrays
- Return type:
array