Add a utility that given a specific localizer position and corresponding

runway info, repositions the localizer and realigns it with the runway
heading so that the approach lines up perfectly.

src/Airports/Makefile.am

@@ -1,6 +1,6 @@
 noinst_LIBRARIES = libAirports.a
 
-noinst_PROGRAMS = gensimple genrunways
+noinst_PROGRAMS = gensimple genrunways calc_loc
 
 libAirports_a_SOURCES = \
 	runways.cxx runways.hxx \
@@ -12,4 +12,7 @@ gensimple_LDADD = libAirports.a -lsgdebug -lsgmisc -lsgxml -lmk4 -lz
 genrunways_SOURCES = genrunways.cxx
 genrunways_LDADD = libAirports.a -lsgdebug -lsgmisc -lsgxml -lmk4 -lz
 
+calc_loc_SOURCES = calc_loc.cxx
+calc_loc_LDADD = -lsgmath
+
 INCLUDES = -I$(top_srcdir) -I$(top_srcdir)/src

src/Airports/calc_loc.cxx

@@ -0,0 +1,61 @@
+// Calculate ILS heading
+
+#include <simgear/compiler.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <iostream>
+#include STL_STRING
+
+#include <plib/sg.h>
+
+#include <simgear/math/sg_geodesy.hxx>
+
+
+SG_USING_STD(string);
+SG_USING_STD(cout);
+SG_USING_STD(endl);
+
+int main( int argc, char **argv ) {
+
+    if ( argc != 9 ) {
+        cout << "Wrong usage" << endl;
+    }
+
+    double loc_lat = atof( argv[1] );
+    double loc_lon = atof( argv[2] );
+    string dir = argv[3];
+    double rwy_lat = atof( argv[4] );
+    double rwy_lon = atof( argv[5] );
+    double rwy_hdg = atof( argv[6] );
+    double rwy_len = atof( argv[7] ) * SG_DEGREES_TO_RADIANS;
+    double rwy_wid = atof( argv[8] );
+
+    if ( dir == "FOR" ) {
+        rwy_hdg += 180.0;
+        if ( rwy_hdg > 360.0 ) {
+            rwy_hdg -= 360.0;
+        }
+    }
+
+    // calculate runway threshold point
+    double thresh_lat, thresh_lon, return_az;
+    geo_direct_wgs_84 ( 0.0, rwy_lat, rwy_lon, rwy_hdg, 
+                        rwy_len / 2.0, &thresh_lat, &thresh_lon, &return_az );
+    cout << "Threshold = " << thresh_lat << "," << thresh_lon << endl;
+
+    // calculate distance from threshold to localizer
+    double az1, az2, dist_m;
+    geo_inverse_wgs_84( 0.0, loc_lat, loc_lon, thresh_lat, thresh_lon,
+                        &az1, &az2, &dist_m );
+    cout << "Distance = " << dist_m << endl;
+
+    // back project that distance along the runway center line
+    double nloc_lat, nloc_lon;
+    geo_direct_wgs_84 ( 0.0, thresh_lat, thresh_lon, rwy_hdg + 180.0, 
+                        dist_m, &nloc_lat, &nloc_lon, &return_az );
+    printf("New localizer = %.6f %.6f\n", nloc_lat, nloc_lon );
+
+    return 0;
+}