1 files changed, 40 insertions, 0 deletions
diff --git a/src/cmd/map/libmap/harrison.c b/src/cmd/map/libmap/harrison.c
new file mode 100644
index 00000000..6b6003c2
--- /dev/null
+++ b/src/cmd/map/libmap/harrison.c
@@ -0,0 +1,40 @@
+#include <u.h>
+#include <libc.h>
+#include "map.h"
+
+static double v3,u2,u3,a,b; /*v=view,p=obj,u=unit.y*/
+
+static int
+Xharrison(struct place *place, double *x, double *y)
+{
+	double p1 = -place->nlat.c*place->wlon.s;
+	double p2 = -place->nlat.c*place->wlon.c;
+	double p3 = place->nlat.s;
+	double d = b + u3*p2 - u2*p3;
+	double t;
+	if(d < .01)
+		return -1;
+	t = a/d;
+	if(v3*place->nlat.s < 1.)
+		return -1;
+	*y = t*p2*u2 + (v3-t*(v3-p3))*u3;
+	*x = t*p1;
+	if(t < 0)
+		return 0;
+	if(*x * *x + *y * *y > 16)
+		return -1;
+	return 1;
+}
+
+proj
+harrison(double r, double alpha)
+{
+	u2 = cos(alpha*RAD);
+	u3 = sin(alpha*RAD);
+	v3 = r;
+	b = r*u2;
+	a = 1 + b;
+	if(r<1.001 || a<sqrt(r*r-1))
+		return 0;
+	return Xharrison;
+}