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tpsts

sofars::projection

Function tpsts 

Source 
pub fn tpsts(xi: f64, eta: f64, a0: f64, b0: f64) -> (f64, f64)
Expand description

In the tangent plane projection, given the star’s rectangular coordinates and the spherical coordinates of the tangent point, solve for the spherical coordinates of the star.

Status: support function.

Given: xi,eta f64 rectangular coordinates of star image (Note 2) a0,b0 f64 tangent point’s spherical coordinates

Returned: a,b f64 star’s spherical coordinates

Notes:

  1. The tangent plane projection is also called the “gnomonic projection” and the “central projection”.

  2. The eta axis points due north in the adopted coordinate system. If the spherical coordinates are observed (RA,Dec), the tangent plane coordinates (xi,eta) are conventionally called the “standard coordinates”. If the spherical coordinates are with respect to a right-handed triad, (xi,eta) are also right-handed. The units of (xi,eta) are, effectively, radians at the tangent point.

  3. All angular arguments are in radians.

  4. This function is a member of the following set:

    spherical      vector         solve for

tpxes         tpxev          xi,eta

    tpsts < tpstv star tpors tporv origin

References:

Calabretta M.R. & Greisen, E.W., 2002, “Representations of celestial coordinates in FITS”, Astron.Astrophys. 395, 1077

Green, R.M., “Spherical Astronomy”, Cambridge University Press, 1987, Chapter 13.