From 28994509cc11ac6a5443054dfae1fedfb69039bc Mon Sep 17 00:00:00 2001
From: rsc <devnull@localhost>
Date: Wed, 21 Apr 2004 22:19:33 +0000
Subject: Why not?

---
 src/cmd/map/libmap/lune.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 src/cmd/map/libmap/lune.c

(limited to 'src/cmd/map/libmap/lune.c')

diff --git a/src/cmd/map/libmap/lune.c b/src/cmd/map/libmap/lune.c
new file mode 100644
index 00000000..dc58c6f0
--- /dev/null
+++ b/src/cmd/map/libmap/lune.c
@@ -0,0 +1,62 @@
+#include <u.h>
+#include <libc.h>
+#include "map.h"
+
+int Xstereographic(struct place *place, double *x, double *y);
+
+static struct place eastpole;
+static struct place westpole;
+static double eastx, easty;
+static double westx, westy;
+static double scale;
+static double pwr;
+
+/* conformal map w = ((1+z)^A - (1-z)^A)/((1+z)^A + (1-z)^A),
+   where A<1, maps unit circle onto a convex lune with x= +-1
+   mapping to vertices of angle A*PI at w = +-1 */
+
+/* there are cuts from E and W poles to S pole,
+   in absence of a cut routine, error is returned for
+   points outside a polar cap through E and W poles */
+
+static int Xlune(struct place *place, double *x, double *y)
+{
+	double stereox, stereoy;
+	double z1x, z1y, z2x, z2y;
+	double w1x, w1y, w2x, w2y;
+	double numx, numy, denx, deny;
+	if(place->nlat.l < eastpole.nlat.l-FUZZ)
+		return	-1;
+	Xstereographic(place, &stereox, &stereoy);
+	stereox *= scale;
+	stereoy *= scale;
+	z1x = 1 + stereox;
+	z1y = stereoy;
+	z2x = 1 - stereox;
+	z2y = -stereoy;
+	cpow(z1x,z1y,&w1x,&w1y,pwr);
+	cpow(z2x,z2y,&w2x,&w2y,pwr);
+	numx = w1x - w2x;
+	numy = w1y - w2y;
+	denx = w1x + w2x;
+	deny = w1y + w2y;
+	cdiv(numx, numy, denx, deny, x, y);
+	return 1;
+}	
+
+proj
+lune(double lat, double theta)
+{
+	deg2rad(lat, &eastpole.nlat);
+	deg2rad(-90.,&eastpole.wlon);
+	deg2rad(lat, &westpole.nlat);
+	deg2rad(90. ,&westpole.wlon);
+	Xstereographic(&eastpole, &eastx, &easty);
+	Xstereographic(&westpole, &westx, &westy);
+	if(fabs(easty)>FUZZ || fabs(westy)>FUZZ ||
+	   fabs(eastx+westx)>FUZZ)
+		abort();
+	scale = 1/eastx;
+	pwr = theta/180;
+	return Xlune;
+}
-- 
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