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#include "astro.h"
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void
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geo(void)
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{
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/*
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 *	uses alpha, delta, rp
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 */
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/*
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 *	sets ra, decl, lha, decl2, az, el
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 */
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/*
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 *	geo converts geocentric equatorial coordinates
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 *	to topocentric equatorial and topocentric horizon
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 *	coordinates.
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 *	All are (usually) referred to the true equator.
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 */
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	double sel, saz, caz;
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	double f;
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	double sa, ca, sd;
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/*
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 *	convert to local hour angle and declination
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 */
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	lha = gst - alpha - wlong;
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	decl = delta;
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/*
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 *	compute diurnal parallax (requires geocentric latitude)
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 */
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	sa = cos(decl)*sin(lha);
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	ca = cos(decl)*cos(lha) - erad*cos(glat)*sin(hp);
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	sd = sin(decl)           - erad*sin(glat)*sin(hp);
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	lha = atan2(sa, ca);
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	decl2 = atan2(sd, sqrt(sa*sa+ca*ca));
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	f = sqrt(sa*sa+ca*ca+sd*sd);
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	semi2 = semi/f;
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	ra = gst - lha - wlong;
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	ra = pinorm(ra);
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/*
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 *	convert to horizon coordinates
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 */
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	sel = sin(nlat)*sin(decl2) + cos(nlat)*cos(decl2)*cos(lha);
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	el = atan2(sel, pyth(sel));
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	saz = sin(lha)*cos(decl2);
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	caz = cos(nlat)*sin(decl2) - sin(nlat)*cos(decl2)*cos(lha);
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	az = pi + atan2(saz, -caz);
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	az /= radian;
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	el /= radian;
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}