1 files changed, 84 insertions, 0 deletions
diff --git a/src/cmd/map/libmap/perspective.c b/src/cmd/map/libmap/perspective.c
new file mode 100644
index 00000000..7ce6b0d6
--- /dev/null
+++ b/src/cmd/map/libmap/perspective.c
@@ -0,0 +1,84 @@
+#include <u.h>
+#include <libc.h>
+#include "map.h"
+
+#define ORTHRAD 1000
+static double viewpt;
+
+static int
+Xperspective(struct place *place, double *x, double *y)
+{
+	double r;
+	if(viewpt<=1+FUZZ && fabs(place->nlat.s<=viewpt+.01))
+		return(-1);
+	r = place->nlat.c*(viewpt - 1.)/(viewpt - place->nlat.s);
+	*x = - r*place->wlon.s;
+	*y = - r*place->wlon.c;
+	if(r>4.)
+		return(-1);
+	if(fabs(viewpt)>1 && place->nlat.s<1/viewpt ||
+	   fabs(viewpt)<=1 && place->nlat.s<viewpt)
+			return 0;
+	return(1);
+}
+
+proj
+perspective(double radius)
+{
+	viewpt = radius;
+	if(viewpt >= ORTHRAD)
+		return(Xorthographic);
+	if(fabs(viewpt-1.)<.0001)
+		return(0);
+	return(Xperspective);
+}
+
+	/* called from various conformal projections,
+           but not from stereographic itself */
+int
+Xstereographic(struct place *place, double *x, double *y)
+{
+	double v = viewpt;
+	int retval;
+	viewpt = -1;
+	retval = Xperspective(place, x, y);
+	viewpt = v;
+	return retval;
+}
+
+proj
+stereographic(void)
+{
+	viewpt = -1.;
+	return(Xperspective);
+}
+
+proj
+gnomonic(void)
+{
+	viewpt = 0.;
+	return(Xperspective);
+}
+
+int
+plimb(double *lat, double *lon, double res)
+{
+	static int first = 1;
+	if(viewpt >= ORTHRAD)
+		return olimb(lat, lon, res);
+	if(first) {
+		first = 0;
+		*lon = -180;
+		if(fabs(viewpt) < .01)
+			*lat = 0;
+		else if(fabs(viewpt)<=1)
+			*lat = asin(viewpt)/RAD;
+		else
+			*lat = asin(1/viewpt)/RAD;
+	} else
+		*lon += res;
+	if(*lon <= 180)
+		return 1;
+	first = 1;
+	return -1;
+}