X-Git-Url: https://git.mxchange.org/?a=blobdiff_plain;f=src%2FCockpit%2Fnavcom.cxx;h=1850539e03a6f6b30eb2e5e62ff811467c537ed7;hb=fee003e8cc17f0aa9a1e9280dd823d20e231e967;hp=541dc2213079422a60874c6966c461852b6826de;hpb=85de2452a3a4e6ebc9d2dc32965b091f7eb328f4;p=flightgear.git

diff --git a/src/Cockpit/navcom.cxx b/src/Cockpit/navcom.cxx
index 541dc2213..1850539e0 100644
--- a/src/Cockpit/navcom.cxx
+++ b/src/Cockpit/navcom.cxx
@@ -2,7 +2,7 @@
 //
 // Written by Curtis Olson, started April 2000.
 //
-// Copyright (C) 2000 - 2002  Curtis L. Olson - curt@flightgear.org
+// Copyright (C) 2000 - 2002  Curtis L. Olson - http://www.flightgear.org/~curt
 //
 // This program is free software; you can redistribute it and/or
 // modify it under the terms of the GNU General Public License as
@@ -28,13 +28,12 @@
 #include <stdio.h>	// snprintf
 
 #include <simgear/compiler.h>
+#include <simgear/sg_inlines.h>
 #include <simgear/math/sg_random.h>
 #include <simgear/math/vector.hxx>
 
 #include <Aircraft/aircraft.hxx>
-#include <Navaids/ilslist.hxx>
 #include <Navaids/navlist.hxx>
-#include <Time/FGEventMgr.hxx>
 
 #include "navcom.hxx"
 
@@ -59,9 +58,16 @@ FGNavCom::FGNavCom() :
     comm_vol_btn(0.0),
     nav_freq(0.0),
     nav_alt_freq(0.0),
+    nav_heading(0.0),
+    nav_radial(0.0),
     nav_target_radial(0.0),
+    nav_target_radial_true(0.0),
+    nav_target_auto_hdg(0.0),
+    nav_gs_rate_of_climb(0.0),
     nav_vol_btn(0.0),
-    nav_ident_btn(true)
+    nav_ident_btn(true),
+    horiz_vel(0.0),
+    last_x(0.0)
 {
     SGPath path( globals->get_fg_root() );
     SGPath term = path;
@@ -102,25 +108,25 @@ FGNavCom::init ()
     fgSetDouble( propname, 60.0 );
     bus_power = fgGetNode( propname, true );
 
-    snprintf(propname, 256, "/instrumentation/comm[%d]/servicable", index);
-    com_servicable = fgGetNode( propname, true );
-    com_servicable->setBoolValue( true );
+    snprintf(propname, 256, "/instrumentation/comm[%d]/serviceable", index);
+    com_serviceable = fgGetNode( propname, true );
+    com_serviceable->setBoolValue( true );
 
-    snprintf(propname, 256, "/instrumentation/nav[%d]/servicable", index);
-    nav_servicable = fgGetNode( propname, true );
-    nav_servicable->setBoolValue( true );
+    snprintf(propname, 256, "/instrumentation/nav[%d]/serviceable", index);
+    nav_serviceable = fgGetNode( propname, true );
+    nav_serviceable->setBoolValue( true );
 
-    snprintf(propname, 256, "/instrumentation/vor[%d]/cdi/servicable", index);
-    cdi_servicable = fgGetNode( propname, true );
-    cdi_servicable->setBoolValue( true );
+    snprintf(propname, 256, "/instrumentation/vor[%d]/cdi/serviceable", index);
+    cdi_serviceable = fgGetNode( propname, true );
+    cdi_serviceable->setBoolValue( true );
 
-    snprintf(propname, 256, "/instrumentation/vor[%d]/gs/servicable", index);
-    gs_servicable = fgGetNode( propname, true );
-    gs_servicable->setBoolValue( true );
+    snprintf(propname, 256, "/instrumentation/vor[%d]/gs/serviceable", index);
+    gs_serviceable = fgGetNode( propname, true );
+    gs_serviceable->setBoolValue( true );
 
-    snprintf(propname, 256, "/instrumentation/vor[%d]/to-from/servicable", index);
-    tofrom_servicable = fgGetNode( propname, true );
-    tofrom_servicable->setBoolValue( true );
+    snprintf(propname, 256, "/instrumentation/vor[%d]/to-from/serviceable", index);
+    tofrom_serviceable = fgGetNode( propname, true );
+    tofrom_serviceable->setBoolValue( true );
 }
 
 void
@@ -180,9 +186,19 @@ FGNavCom::bind ()
            &FGNavCom::get_audio_btn, &FGNavCom::set_audio_btn );
     fgSetArchivable( propname );
 
+    snprintf(propname, 256, "/radios/nav[%d]/heading-deg", index);
+    fgTie( propname,  this, &FGNavCom::get_nav_heading );
+
     snprintf(propname, 256, "/radios/nav[%d]/radials/actual-deg", index);
     fgTie( propname,  this, &FGNavCom::get_nav_radial );
 
+    snprintf(propname, 256, "/radios/nav[%d]/radials/target-radial-deg", index);
+    fgTie( propname,  this, &FGNavCom::get_nav_target_radial_true );
+
+    snprintf(propname, 256, "/radios/nav[%d]/radials/target-auto-hdg-deg",
+             index);
+    fgTie( propname,  this, &FGNavCom::get_nav_target_auto_hdg );
+
     snprintf(propname, 256, "/radios/nav[%d]/to-flag", index);
     fgTie( propname, this, &FGNavCom::get_nav_to_flag );
 
@@ -195,9 +211,18 @@ FGNavCom::bind ()
     snprintf(propname, 256, "/radios/nav[%d]/heading-needle-deflection", index);
     fgTie( propname, this, &FGNavCom::get_nav_cdi_deflection );
 
+    snprintf(propname, 256, "/radios/nav[%d]/crosstrack-error-m", index);
+    fgTie( propname, this, &FGNavCom::get_nav_cdi_xtrack_error );
+
     snprintf(propname, 256, "/radios/nav[%d]/has-gs", index);
     fgTie( propname, this, &FGNavCom::get_nav_has_gs );
 
+    snprintf(propname, 256, "/radios/nav[%d]/nav-loc", index);
+    fgTie( propname, this, &FGNavCom::get_nav_loc );
+
+    snprintf(propname, 256, "/radios/nav[%d]/gs-rate-of-climb", index);
+    fgTie( propname, this, &FGNavCom::get_nav_gs_rate_of_climb );
+
     snprintf(propname, 256, "/radios/nav[%d]/gs-needle-deflection", index);
     fgTie( propname, this, &FGNavCom::get_nav_gs_deflection );
 
@@ -293,7 +318,7 @@ double FGNavCom::adjustNavRange( double stationElev, double aircraftElev,
 
 // model standard ILS service volumes as per AIM 1-1-9
 double FGNavCom::adjustILSRange( double stationElev, double aircraftElev,
-				     double offsetDegrees, double distance )
+                                 double offsetDegrees, double distance )
 {
     // assumptions we model the standard service volume, plus
 
@@ -316,7 +341,7 @@ double FGNavCom::adjustILSRange( double stationElev, double aircraftElev,
 //     } else {
 // 	return 0;
 //     }
-    return FG_ILS_DEFAULT_RANGE;
+    return FG_LOC_DEFAULT_RANGE;
 }
 
 
@@ -339,7 +364,7 @@ FGNavCom::update(double dt)
     ////////////////////////////////////////////////////////////////////////
 
     if ( nav_valid && power_btn && (bus_power->getDoubleValue() > 1.0)
-         && nav_servicable->getBoolValue() )
+         && nav_serviceable->getBoolValue() )
     {
 	station = Point3D( nav_x, nav_y, nav_z );
 	nav_loc_dist = aircraft.distance3D( station );
@@ -353,9 +378,9 @@ FGNavCom::update(double dt)
             double dist = sgdClosestPointToLineDistSquared( p, p0,
                                                             gs_base_vec );
             nav_gs_dist = sqrt( dist );
-            // cout << nav_gs_dist;
+            // cout << "nav_gs_dist = " << nav_gs_dist << endl;
 
-            // Point3D tmp( nav_gs_x, nav_gs_y, nav_gs_z );
+            Point3D tmp( nav_gs_x, nav_gs_y, nav_gs_z );
             // cout << " (" << aircraft.distance3D( tmp ) << ")" << endl;
 
             // wgs84 heading to glide slope (to determine sign of distance)
@@ -386,7 +411,7 @@ FGNavCom::update(double dt)
                             lat * SGD_RADIANS_TO_DEGREES,
                             lon * SGD_RADIANS_TO_DEGREES, 
 			    nav_loclat, nav_loclon,
-			    &az1, &az2, &s );
+			    &nav_heading, &az2, &s );
 	// cout << "az1 = " << az1 << " magvar = " << nav_magvar << endl;
 	nav_radial = az2 - nav_twist;
 	// cout << " heading = " << nav_heading
@@ -397,10 +422,11 @@ FGNavCom::update(double dt)
 	    while ( offset < -180.0 ) { offset += 360.0; }
 	    while ( offset > 180.0 ) { offset -= 360.0; }
 	    // cout << "ils offset = " << offset << endl;
-	    nav_effective_range = adjustILSRange(nav_elev, elev, offset,
-						  nav_loc_dist * SG_METER_TO_NM );
+	    nav_effective_range
+                = adjustILSRange( nav_elev, elev, offset,
+                                  nav_loc_dist * SG_METER_TO_NM );
 	} else {
-	    nav_effective_range = adjustNavRange(nav_elev, elev, nav_range);
+	    nav_effective_range = adjustNavRange( nav_elev, elev, nav_range );
 	}
 	// cout << "nav range = " << nav_effective_range
 	//      << " (" << nav_range << ")" << endl;
@@ -418,18 +444,104 @@ FGNavCom::update(double dt)
 	if ( !nav_loc ) {
 	    nav_target_radial = nav_sel_radial;
 	}
+
+        // Calculate some values for the nav/ils hold autopilot
+
+        double cur_radial = get_nav_reciprocal_radial();
+        if ( nav_loc ) {
+            // ILS localizers radials are already "true" in our
+            // database
+        } else {
+            cur_radial += nav_twist;
+        }
+        if ( get_nav_from_flag() ) {
+            cur_radial += 180.0;
+            while ( cur_radial >= 360.0 ) { cur_radial -= 360.0; }
+        }
+        
+        // AUTOPILOT HELPERS
+
+        // determine the target radial in "true" heading
+        nav_target_radial_true = nav_target_radial;
+        if ( nav_loc ) {
+            // ILS localizers radials are already "true" in our
+            // database
+        } else {
+            // VOR radials need to have that vor's offset added in
+            nav_target_radial_true += nav_twist;
+        }
+
+        while ( nav_target_radial_true < 0.0 ) {
+            nav_target_radial_true += 360.0;
+        }
+        while ( nav_target_radial_true > 360.0 ) {
+            nav_target_radial_true -= 360.0;
+        }
+
+        // determine the heading adjustment needed.
+        // over 8km scale by 3.0 
+        //    (3 is chosen because max deflection is 10
+        //    and 30 is clamped angle to radial)
+        // under 8km scale by 10.0
+        //    because the overstated error helps drive it to the radial in a 
+        //    moderate cross wind.
+        double adjustment = 0.0;
+        if (nav_loc_dist > 8000) {
+            adjustment = get_nav_cdi_deflection() * 3.0;
+        } else {
+            adjustment = get_nav_cdi_deflection() * 10.0;
+        }
+        SG_CLAMP_RANGE( adjustment, -30.0, 30.0 );
+        
+        // determine the target heading to fly to intercept the
+        // tgt_radial
+        nav_target_auto_hdg = nav_target_radial_true + adjustment; 
+        while ( nav_target_auto_hdg <   0.0 ) { nav_target_auto_hdg += 360.0; }
+        while ( nav_target_auto_hdg > 360.0 ) { nav_target_auto_hdg -= 360.0; }
+
+        // cross track error
+        // ????
+
+        // Calculate desired rate of climb for intercepting the GS
+        double x = nav_gs_dist;
+        double y = (alt_node->getDoubleValue() - nav_elev)
+            * SG_FEET_TO_METER;
+        double current_angle = atan2( y, x ) * SGD_RADIANS_TO_DEGREES;
+
+        double target_angle = nav_target_gs;
+        double gs_diff = target_angle - current_angle;
+
+        // convert desired vertical path angle into a climb rate
+        double des_angle = current_angle - 10 * gs_diff;
+
+        // estimate horizontal speed towards ILS in meters per minute
+        double dist = last_x - x;
+        last_x = x;
+        if ( dt > 0.0 ) {
+            // avoid nan
+            double new_vel = ( dist / dt );
+ 
+            horiz_vel = 0.75 * horiz_vel + 0.25 * new_vel;
+            // double horiz_vel = cur_fdm_state->get_V_ground_speed()
+            //    * SG_FEET_TO_METER * 60.0;
+            // double horiz_vel = airspeed_node->getFloatValue()
+            //    * SG_FEET_TO_METER * 60.0;
+
+            nav_gs_rate_of_climb = -sin( des_angle * SGD_DEGREES_TO_RADIANS )
+                * horiz_vel * SG_METER_TO_FEET;
+        }
     } else {
 	nav_inrange = false;
 	// cout << "not picking up vor. :-(" << endl;
     }
 
-    if ( nav_valid && nav_inrange && nav_servicable->getBoolValue() ) {
+    if ( nav_valid && nav_inrange && nav_serviceable->getBoolValue() ) {
 	// play station ident via audio system if on + ident,
 	// otherwise turn it off
 	if ( power_btn && (bus_power->getDoubleValue() > 1.0)
              && nav_ident_btn && audio_btn )
         {
-	    SGSimpleSound *sound;
+	    SGSoundSample *sound;
 	    sound = globals->get_soundmgr()->find( nav_fx_name );
             if ( sound != NULL ) {
                 sound->set_volume( nav_vol_btn );
@@ -485,63 +597,84 @@ void FGNavCom::search()
     double lat = lat_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
     double elev = alt_node->getDoubleValue() * SG_FEET_TO_METER;
 
-    FGILS *ils;
-    FGNav *nav;
+    FGNavRecord *nav = NULL;
+    FGNavRecord *loc = NULL;
+    FGNavRecord *dme = NULL;
+    FGNavRecord *gs = NULL;
 
     ////////////////////////////////////////////////////////////////////////
     // Nav.
     ////////////////////////////////////////////////////////////////////////
 
-    if ( (ils = current_ilslist->findByFreq(nav_freq, lon, lat, elev)) != NULL ) {
-	nav_id = ils->get_locident();
+    nav = globals->get_navlist()->findByFreq(nav_freq, lon, lat, elev);
+    dme = globals->get_dmelist()->findByFreq(nav_freq, lon, lat, elev);
+    if ( nav == NULL ) {
+        loc = globals->get_loclist()->findByFreq(nav_freq, lon, lat, elev);
+        gs = globals->get_gslist()->findByFreq(nav_freq, lon, lat, elev);
+    }
+        
+    if ( loc != NULL ) {
+	nav_id = loc->get_ident();
+        // cout << "localizer = " << nav_id << endl;
 	nav_valid = true;
 	if ( last_nav_id != nav_id || last_nav_vor ) {
-	    nav_trans_ident = ils->get_trans_ident();
+	    nav_trans_ident = loc->get_trans_ident();
+	    nav_target_radial = loc->get_multiuse();
+	    while ( nav_target_radial <   0.0 ) { nav_target_radial += 360.0; }
+	    while ( nav_target_radial > 360.0 ) { nav_target_radial -= 360.0; }
+	    nav_loclon = loc->get_lon();
+	    nav_loclat = loc->get_lat();
+	    nav_x = loc->get_x();
+	    nav_y = loc->get_y();
+	    nav_z = loc->get_z();
 	    last_nav_id = nav_id;
 	    last_nav_vor = false;
 	    nav_loc = true;
-	    nav_has_dme = ils->get_has_dme();
-	    nav_has_gs = ils->get_has_gs();
-
-	    nav_loclon = ils->get_loclon();
-	    nav_loclat = ils->get_loclat();
-	    nav_gslon = ils->get_gslon();
-	    nav_gslat = ils->get_gslat();
-	    nav_elev = ils->get_gselev();
+	    nav_has_dme = (dme != NULL);
+            nav_has_gs = (gs != NULL);
+            if ( nav_has_gs ) {
+                nav_gslon = gs->get_lon();
+                nav_gslat = gs->get_lat();
+                nav_elev = gs->get_elev_ft();
+                int tmp = (int)(gs->get_multiuse() / 1000.0);
+                nav_target_gs = (double)tmp / 100.0;
+                nav_gs_x = gs->get_x();
+                nav_gs_y = gs->get_y();
+                nav_gs_z = gs->get_z();
+
+                // derive GS baseline (perpendicular to the runay
+                // along the ground)
+                double tlon, tlat, taz;
+                geo_direct_wgs_84 ( 0.0, nav_gslat, nav_gslon,
+                                    nav_target_radial + 90,  
+                                    100.0, &tlat, &tlon, &taz );
+                // cout << "nav_target_radial = " << nav_target_radial << endl;
+                // cout << "nav_loc = " << nav_loc << endl;
+                // cout << nav_gslon << "," << nav_gslat << "  "
+                //      << tlon << "," << tlat << "  (" << nav_elev << ")"
+                //      << endl;
+                Point3D p1 = sgGeodToCart( Point3D(tlon*SGD_DEGREES_TO_RADIANS,
+                                                   tlat*SGD_DEGREES_TO_RADIANS,
+                                                   nav_elev*SG_FEET_TO_METER)
+                                           );
+                // cout << nav_gs_x << "," << nav_gs_y << "," << nav_gs_z
+                //      << endl;
+                // cout << p1 << endl;
+                sgdSetVec3( gs_base_vec,
+                            p1.x()-nav_gs_x, p1.y()-nav_gs_y, p1.z()-nav_gs_z );
+                // cout << gs_base_vec[0] << "," << gs_base_vec[1] << ","
+                //      << gs_base_vec[2] << endl;
+            } else {
+                nav_elev = loc->get_elev_ft();
+            }
 	    nav_twist = 0;
-	    nav_range = FG_ILS_DEFAULT_RANGE;
+	    nav_range = FG_LOC_DEFAULT_RANGE;
 	    nav_effective_range = nav_range;
-	    nav_target_gs = ils->get_gsangle();
-	    nav_target_radial = ils->get_locheading();
-	    while ( nav_target_radial <   0.0 ) { nav_target_radial += 360.0; }
-	    while ( nav_target_radial > 360.0 ) { nav_target_radial -= 360.0; }
-	    nav_x = ils->get_x();
-	    nav_y = ils->get_y();
-	    nav_z = ils->get_z();
-	    nav_gs_x = ils->get_gs_x();
-	    nav_gs_y = ils->get_gs_y();
-	    nav_gs_z = ils->get_gs_z();
-
-            // derive GS baseline
-            double tlon, tlat, taz;
-            geo_direct_wgs_84 ( 0.0, nav_gslat, nav_gslon, nav_target_radial + 90,  
-                                100.0, &tlat, &tlon, &taz );
-            // cout << nav_gslon << "," << nav_gslat << "  "
-            //      << tlon << "," << tlat << "  (" << nav_elev << ")" << endl;
-            Point3D p1 = sgGeodToCart( Point3D(tlon*SGD_DEGREES_TO_RADIANS,
-                                               tlat*SGD_DEGREES_TO_RADIANS,
-                                               nav_elev*SG_FEET_TO_METER) );
-            // cout << nav_gs_x << "," << nav_gs_y << "," << nav_gs_z << endl;
-            // cout << p1 << endl;
-            sgdSetVec3( gs_base_vec,
-                        p1.x()-nav_gs_x, p1.y()-nav_gs_y, p1.z()-nav_gs_z );
-            // cout << gs_base_vec[0] << "," << gs_base_vec[1] << ","
-            //      << gs_base_vec[2] << endl;
 
 	    if ( globals->get_soundmgr()->exists( nav_fx_name ) ) {
 		globals->get_soundmgr()->remove( nav_fx_name );
 	    }
-	    SGSimpleSound *sound;
+	    SGSoundSample *sound;
 	    sound = morse.make_ident( nav_trans_ident, LO_FREQUENCY );
 	    sound->set_volume( 0.3 );
 	    globals->get_soundmgr()->add( sound, nav_fx_name );
@@ -563,23 +696,24 @@ void FGNavCom::search()
 	    //      << " current time = "
 	    //      << globals->get_time_params()->get_cur_time() << endl;
 
-	    // cout << "Found an ils station in range" << endl;
-	    // cout << " id = " << ils->get_locident() << endl;
+	    // cout << "Found an loc station in range" << endl;
+	    // cout << " id = " << loc->get_locident() << endl;
 	}
-    } else if ( (nav = current_navlist->findByFreq(nav_freq, lon, lat, elev)) != NULL ) {
+    } else if ( nav != NULL ) {
 	nav_id = nav->get_ident();
-	nav_valid = (nav->get_type() == 'V');
+        // cout << "nav = " << nav_id << endl;
+	nav_valid = true;
 	if ( last_nav_id != nav_id || !last_nav_vor ) {
 	    last_nav_id = nav_id;
 	    last_nav_vor = true;
 	    nav_trans_ident = nav->get_trans_ident();
 	    nav_loc = false;
-	    nav_has_dme = nav->get_has_dme();
+	    nav_has_dme = (dme != NULL);
 	    nav_has_gs = false;
 	    nav_loclon = nav->get_lon();
 	    nav_loclat = nav->get_lat();
-	    nav_elev = nav->get_elev();
-	    nav_twist = nav->get_magvar();
+	    nav_elev = nav->get_elev_ft();
+	    nav_twist = nav->get_multiuse();
 	    nav_range = nav->get_range();
 	    nav_effective_range = adjustNavRange(nav_elev, elev, nav_range);
 	    nav_target_gs = 0.0;
@@ -591,7 +725,7 @@ void FGNavCom::search()
 	    if ( globals->get_soundmgr()->exists( nav_fx_name ) ) {
 		globals->get_soundmgr()->remove( nav_fx_name );
 	    }
-	    SGSimpleSound *sound;
+	    SGSoundSample *sound;
 	    sound = morse.make_ident( nav_trans_ident, LO_FREQUENCY );
 	    sound->set_volume( 0.3 );
 	    if ( globals->get_soundmgr()->add( sound, nav_fx_name ) ) {
@@ -640,7 +774,7 @@ double FGNavCom::get_nav_cdi_deflection() const {
     double r;
 
     if ( nav_inrange
-         && nav_servicable->getBoolValue() && cdi_servicable->getBoolValue() )
+         && nav_serviceable->getBoolValue() && cdi_serviceable->getBoolValue() )
     {
         r = nav_radial - nav_target_radial;
 	// cout << "Target radial = " << nav_target_radial 
@@ -663,12 +797,39 @@ double FGNavCom::get_nav_cdi_deflection() const {
     return r;
 }
 
+// return the amount of cross track distance error, returns a meters
+double FGNavCom::get_nav_cdi_xtrack_error() const {
+    double r, m;
+
+    if ( nav_inrange
+         && nav_serviceable->getBoolValue() && cdi_serviceable->getBoolValue() )
+    {
+        r = nav_radial - nav_target_radial;
+	// cout << "Target radial = " << nav_target_radial 
+	//     << "  Actual radial = " << nav_radial
+        //     << "  r = " << r << endl;
+    
+	while ( r >  180.0 ) { r -= 360.0;}
+	while ( r < -180.0 ) { r += 360.0;}
+	if ( fabs(r) > 90.0 )
+	    r = ( r<0.0 ? -r-180.0 : -r+180.0 );
+
+        r = -r;                 // reverse, since radial is outbound
+
+        m = nav_loc_dist * sin(r * SGD_DEGREES_TO_RADIANS);
+
+    } else {
+	m = 0.0;
+    }
+
+    return m;
+}
 
 // return the amount of glide slope needle deflection (.i.e. the
 // number of degrees we are off the glide slope * 5.0
 double FGNavCom::get_nav_gs_deflection() const {
     if ( nav_inrange && nav_has_gs
-         && nav_servicable->getBoolValue() && gs_servicable->getBoolValue() )
+         && nav_serviceable->getBoolValue() && gs_serviceable->getBoolValue() )
     {
 	double x = nav_gs_dist;
 	double y = (fgGetDouble("/position/altitude-ft") - nav_elev)
@@ -689,8 +850,8 @@ bool
 FGNavCom::get_nav_to_flag () const
 {
     if ( nav_inrange
-         && nav_servicable->getBoolValue()
-         && tofrom_servicable->getBoolValue() )
+         && nav_serviceable->getBoolValue()
+         && tofrom_serviceable->getBoolValue() )
     {
         double offset = fabs(nav_radial - nav_target_radial);
         if (nav_loc) {
@@ -711,8 +872,8 @@ bool
 FGNavCom::get_nav_from_flag () const
 {
     if ( nav_inrange
-         && nav_servicable->getBoolValue()
-         && tofrom_servicable->getBoolValue() ) {
+         && nav_serviceable->getBoolValue()
+         && tofrom_serviceable->getBoolValue() ) {
         double offset = fabs(nav_radial - nav_target_radial);
         if (nav_loc) {
             return false;
@@ -725,6 +886,16 @@ FGNavCom::get_nav_from_flag () const
 }
 
 
+/**
+ * Return the true heading to station
+ */
+double
+FGNavCom::get_nav_heading () const
+{
+    return nav_heading;
+}
+
+
 /**
  * Return the current radial.
  */