Initial commit

1 files changed, 51 insertions, 0 deletions

diff --git a/noao/astutil/asttools/refrac.x b/noao/astutil/asttools/refrac.x
new file mode 100644
index 00000000..2834ff5f
--- /dev/null
+++ b/noao/astutil/asttools/refrac.x
@@ -0,0 +1,51 @@
+include	<math.h>
+
+
+# REFRAC -- Compute observed place from apparent place.
+#
+# This is a placeholder routine.  I am not completely sure this is
+# done correctly though the SLALIB routines are accurate.
+# This uses the quick (less precise) SLALIB routines for the
+# calculation.
+
+procedure refrac (ara, adec, aha, lat, w, t, p, h, ora, odec)
+
+double	ara, adec			# Apparent ra (hr) and dec (deg)
+double	aha				# Apparent hour angle (hr)
+double	lat				# Latitude (deg)
+double	w				# Effective wavelength (A)
+double	t				# Temperature (C)
+double	p				# Pressure (mbar)
+double	h				# Humidity (frac 0-1)
+double	ora, odec			# Observed ra (hr) and dec (deg)
+
+double	oha, refa, refb, az, el, vu[3], vr[3]
+
+begin
+	# Determine refraction coefficients.
+	call slRFCQ (t+273.15D0, p, h, w/10000D0, refa, refb)
+
+	# Convert (aha,adec) to (az,el).
+	call slDE2H (DEGTORAD(aha*15D0), DEGTORAD(adec), DEGTORAD(lat), az, el)
+
+	# Convert (az,el) to (x,y,z).
+	call slDS2C (az, el, vu)
+
+	# Apply refraction correction.
+	call slREFV (vu, refa, refb, vr)
+
+	# Convert (x,y,z) to (az,el)
+	call slDC2S (vr, az, el)
+
+	# Convert (az,el) to (ha,dec).
+	call slDH2E (az, el, DEGTORAD(lat), oha, odec)
+
+	# Convert (oha,odec) to (ora,odec).
+	oha = RADTODEG(oha) / 15D0
+	odec = RADTODEG(odec)
+	ora = ara + aha - oha
+	if (ara - ora < -12)
+	    ora = ora + 24
+	else if (ara - ora > 12)
+	    ora = ora - 24
+end