From cd5bae7871bc0f0bc68b4d2a84703929a7a3c9d1 Mon Sep 17 00:00:00 2001
From: wkj <devnull@localhost>
Date: Wed, 21 Apr 2004 02:16:43 +0000
Subject: Astro with some minor changes to placate Unix.

---
 src/cmd/astro/geo.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 src/cmd/astro/geo.c

(limited to 'src/cmd/astro/geo.c')

diff --git a/src/cmd/astro/geo.c b/src/cmd/astro/geo.c
new file mode 100644
index 00000000..de562210
--- /dev/null
+++ b/src/cmd/astro/geo.c
@@ -0,0 +1,60 @@
+#include "astro.h"
+
+void
+geo(void)
+{
+
+/*
+ *	uses alpha, delta, rp
+ */
+
+/*
+ *	sets ra, decl, lha, decl2, az, el
+ */
+
+/*
+ *	geo converts geocentric equatorial coordinates
+ *	to topocentric equatorial and topocentric horizon
+ *	coordinates.
+ *	All are (usually) referred to the true equator.
+ */
+
+	double sel, saz, caz;
+	double f;
+	double sa, ca, sd;
+
+/*
+ *	convert to local hour angle and declination
+ */
+
+	lha = gst - alpha - wlong;
+	decl = delta;
+
+/*
+ *	compute diurnal parallax (requires geocentric latitude)
+ */
+
+	sa = cos(decl)*sin(lha);
+	ca = cos(decl)*cos(lha) - erad*cos(glat)*sin(hp);
+	sd = sin(decl)           - erad*sin(glat)*sin(hp);
+
+	lha = atan2(sa, ca);
+	decl2 = atan2(sd, sqrt(sa*sa+ca*ca));
+	f = sqrt(sa*sa+ca*ca+sd*sd);
+	semi2 = semi/f;
+	ra = gst - lha - wlong;
+	ra = pinorm(ra);
+
+/*
+ *	convert to horizon coordinates
+ */
+
+	sel = sin(nlat)*sin(decl2) + cos(nlat)*cos(decl2)*cos(lha);
+	el = atan2(sel, pyth(sel));
+	saz = sin(lha)*cos(decl2);
+	caz = cos(nlat)*sin(decl2) - sin(nlat)*cos(decl2)*cos(lha);
+	az = pi + atan2(saz, -caz);
+
+	az /= radian;
+	el /= radian;
+}
-- 
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