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include <math.h>
# AST_VR -- Project a velocity vector in radial velocity along line of sight.
procedure ast_vr (ra1, dec1, v1, ra2, dec2, v2)
double ra1 # Right ascension of velocity vector (hours)
double dec1 # Declination of velocity vector (degrees)
double v1 # Magnitude of velocity vector
double ra2 # Right ascension of observation (hours)
double dec2 # Declination of observation (degrees)
double v2 # Radial velocity along direction of observation
double vx, vy, vz, cc, cs, s
begin
# Cartisian velocity components of the velocity vector.
vx = v1 * cos (DEGTORAD (15. * ra1)) * cos (DEGTORAD (dec1))
vy = v1 * sin (DEGTORAD (15. * ra1)) * cos (DEGTORAD (dec1))
vz = v1 * sin (DEGTORAD (dec1))
# Direction cosines along the direction of observation.
cc = cos (DEGTORAD (dec2)) * cos (DEGTORAD (15. * ra2))
cs = cos (DEGTORAD (dec2)) * sin (DEGTORAD (15. * ra2))
s = sin (DEGTORAD (dec2))
# Project velocity vector along the direction of observation.
v2 = (vx * cc + vy * cs + vz * s)
end
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