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Diffstat (limited to 'noao/astutil/asttools/astgalactic.x')
| -rw-r--r-- | noao/astutil/asttools/astgalactic.x | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/noao/astutil/asttools/astgalactic.x b/noao/astutil/asttools/astgalactic.x new file mode 100644 index 00000000..ab51a918 --- /dev/null +++ b/noao/astutil/asttools/astgalactic.x @@ -0,0 +1,52 @@ +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 |