Correction of short path azimuth calculation by Dave Freese, W1HKJ

in the qrb function.


git-svn-id: https://hamlib.svn.sourceforge.net/svnroot/hamlib/trunk@2536 7ae35d74-ebe9-4afe-98af-79ac388436b8

src/locator.c

@@ -18,7 +18,7 @@
  *  Copyright (c) 2003 by Nate Bargmann
  *  Copyright (c) 2003 by Dave Hines
  *
- *	$Id: locator.c,v 1.19 2006-10-15 00:27:51 aa6e Exp $
+ *	$Id: locator.c,v 1.20 2008-12-29 13:12:29 n0nb Exp $
  *
  *  Code to determine bearing and range was taken from the Great Circle,
  *  by S. R. Sampson, N5OWK.
@@ -539,29 +539,22 @@ int HAMLIB_API qrb(double lon1, double lat1, double lon2, double lat2, double *d
 	 * This method is easier than the one in the handbook
 	 */
 
-	/* Short Path */
+	
 	*distance = ARC_IN_KM * RADIAN * arc;
 
-	/* This formula seems to work with very small distances
+	/* Short Path */
-	 *
+	/* Change to azimuth computation by Dave Freese, W1HKJ */
-	 * I found it on the Web at:
+
-	 * http://williams.best.vwh.net/avform.htm#Crs
+	az = RADIAN * atan2(sin(lon2 - lon1) * cos(lat2),
-	 *
+			    (cos(lat1) * sin(lat2) - sin(lat1) * cos(lat2) * cos(lon2 - lon1)));
-	 * Strangely, all the computed values were negative thus the
+
-	 * sign reversal below.
+	az = fmod(360.0 + az, 360.0);
-	 * - N0NB
+	if (az < 0.0)
-	 */
+		az += 360.0;
-	az = RADIAN * fmod(atan2(sin(lon1 - lon2) * cos(lat2),
+	else if (az >= 360.0)
-				 cos(lat1) * sin(lat2) - sin(lat1) * cos(lat2) * cos(lon1 - lon2)), 2 * M_PI);
+		az -= 360.0;
-	if (lon1 > lon2) {
+
-		az -= 360.;
+	*azimuth = floor(az + 0.5);
-		*azimuth = -az;
-	} else {
-		if (az >= 0.0)
-			*azimuth = az;
-		else
-			*azimuth = -az;
-	}
 	return RIG_OK;
 }