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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
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