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include <mach.h>
include <math.h>
# Definition of system
define LONGNCP 123.00d0 # Longtitude of NCP
define RAGPOLE 192.25d0 # RA Galactic Pole (12:49)
define DECGPOLE 27.4d0 # DEC Galactic Pole (27:24)
define GEPOCH 1950.0d0 # Epoch of definition
# AST_GALACTIC -- Convert equatorial coordinates to galactic coordinates.
# Input coordinates and epoch are changed to epoch of galactic coordinates.
procedure ast_galactic (ra, dec, epoch, lii, bii)
double ra # Right ascension (hours)
double dec # Declination (degrees)
double epoch # Epoch of coordinates
double lii # Galactic longitude (degrees)
double bii # Galactic latitude (degrees)
double rar, decr, drar, cosdecg, sindecg, cosdecr, x, y, z, r, temp
begin
# Precess the coordinates to 1950.0
call ast_precess (ra, dec, epoch, rar, decr, double (GEPOCH))
# Precompute the necessary constants.
drar = DEGTORAD (15.0d0 * rar - RAGPOLE)
cosdecg = cos (DEGTORAD (DECGPOLE))
sindecg = sin (DEGTORAD(DECGPOLE))
cosdecr = cos (DEGTORAD (decr))
# Compute the tansformation equations
x = cosdecr * cos (drar)
y = cosdecr * sin (drar)
z = sin (DEGTORAD (decr))
temp = z * cosdecg - x * sindecg
z = z * sindecg + x * cosdecg
x = temp
r = sqrt (x * x + y * y)
# Compute lii and bii and convert to degrees.
if (r < EPSILOND)
lii = 0.0d0
else
lii = DEGTORAD (LONGNCP) + atan2 (-y, x)
if (lii < 0.0d0)
lii = lii + TWOPI
bii = atan2 (z, r)
lii = RADTODEG (lii)
bii = RADTODEG (bii)
end
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