Read antenna radiation pattern from file

src/Radio/antenna.cxx

@@ -32,17 +32,37 @@ using namespace std;
 
 FGRadioAntenna::FGRadioAntenna(string type) {
 	
-	_mirror_y = 1;
+	_mirror_y = 1;	// normally we want to mirror these axis because the pattern is simetric
 	_mirror_z = 1;
 	_invert_ground = 0;		
 	load_antenna_pattern(type);
 }
 
 FGRadioAntenna::~FGRadioAntenna() {
+	_pattern.clear();
 	
 }
 
-double FGRadioAntenna::calculate_gain(double azimuth, double elevation) {
+double FGRadioAntenna::calculate_gain(double bearing, double angle) {
+	
+	// TODO: what if the pattern is assimetric?
+	bearing = fabs(bearing);
+	if (bearing > 180)
+		bearing = 360 - bearing;
+	// for plots with 2 degrees resolution:
+	int azimuth = (int)floor(bearing);
+	azimuth += azimuth % 2;
+	int elevation = (int)floor(angle);
+	elevation += elevation % 2;
+	
+	for (unsigned int i =0; i < _pattern.size(); i++) {
+		AntennaGain point_gain = _pattern[i];
+		
+		if ( (azimuth == point_gain.azimuth) && (elevation == point_gain.elevation)) {
+			return point_gain.gain;
+		}
+	}
+		
 	return 0;
 }
 
@@ -63,10 +83,16 @@ void FGRadioAntenna::load_antenna_pattern(string type) {
 	double gain;
 	while(!file_in.eof()) {
 		file_in >> heading >> elevation >> gain;
-		cerr << "head: " << heading << " elev: " << elevation << " gain: " << gain << endl;
+		if( (_mirror_y == 1) && (heading > 180) ) {
+			continue;
+		}
+		if ( (_mirror_z == 1) && (elevation < 0) ) {
+			continue;
+		}
+		//cerr << "head: " << heading << " elev: " << elevation << " gain: " << gain << endl;
 		AntennaGain datapoint;
 		datapoint.azimuth = heading;
-		datapoint.elevation = elevation;
+		datapoint.elevation = 90.0 - fabs(elevation);
 		datapoint.gain = gain;
 		_pattern.push_back(datapoint);
 	}

src/Radio/antenna.hxx

@@ -51,7 +51,7 @@ public:
 	
 	FGRadioAntenna(string type);
     ~FGRadioAntenna();
-	double calculate_gain(double azimuth, double elevation);
+	double calculate_gain(double bearing, double angle);
-	
+	void set_heading(double heading_deg) {_heading_deg = heading_deg ;};
-	
+	void set_elevation_angle(double elevation_angle_deg) {_elevation_angle_deg = elevation_angle_deg ;};
 };

src/Radio/radio.cxx

@@ -66,6 +66,8 @@ FGRadioTransmission::FGRadioTransmission() {
 	
 	_root_node = fgGetNode("sim/radio", true);
 	_terrain_sampling_distance = _root_node->getDoubleValue("sampling-distance", 90.0); // regular SRTM is 90 meters
+	
+	
 }
 
 FGRadioTransmission::~FGRadioTransmission() 
@@ -202,11 +204,8 @@ double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, i
 	double eps_dielect=15.0;
 	double sgm_conductivity = 0.005;
 	double eno = 301.0;
-	double frq_mhz;
+	double frq_mhz = freq;
-	if( (freq < 118.0) || (freq > 137.0) )
+	
-		frq_mhz = 125.0; 	// sane value, middle of bandplan
-	else
-		frq_mhz = freq;
 	int radio_climate = 5;		// continental temperate
 	int pol= _polarization;	
 	double conf = 0.90;	// 90% of situations and time, take into account speed
@@ -233,6 +232,7 @@ double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, i
 	double own_lat = fgGetDouble("/position/latitude-deg");
 	double own_lon = fgGetDouble("/position/longitude-deg");
 	double own_alt_ft = fgGetDouble("/position/altitude-ft");
+	double own_heading = fgGetDouble("/orientation/heading-deg");
 	double own_alt= own_alt_ft * SG_FEET_TO_METER;
 	
 	
@@ -257,6 +257,7 @@ double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, i
 	
 	double point_distance= _terrain_sampling_distance; 
 	double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
+	double reverse_course = SGGeodesy::courseRad(sender_pos_c, own_pos_c);
 	double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 	double probe_distance = 0.0;
 	/** If distance larger than this value (300 km), assume reception imposssible */
@@ -400,6 +401,22 @@ double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, i
 	//cerr << "Clutter loss: " << clutter_loss << endl;
 	//if (errnum == 4)	// if parameters are outside sane values for lrprop, the alternative method is used
 	//	return -1;
+	double sender_heading = 270.0; // due West
+	double tx_antenna_bearing = sender_heading - reverse_course;
+	double rx_antenna_bearing = own_heading - course;
+	double rx_elev_angle = atan((itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m) * SGD_RADIANS_TO_DEGREES;
+	double tx_elev_angle = 0.0 - rx_elev_angle;
+	_TX_antenna = new FGRadioAntenna("Plot2");
+	_TX_antenna->set_heading(sender_heading);
+	_TX_antenna->set_elevation_angle(0);
+	double tx_pattern_gain = _TX_antenna->calculate_gain(tx_antenna_bearing, tx_elev_angle);
+	_RX_antenna = new FGRadioAntenna("Plot2");
+	_RX_antenna->set_heading(own_heading);
+	_RX_antenna->set_elevation_angle(fgGetDouble("/orientation/pitch-deg"));
+	double rx_pattern_gain = _RX_antenna->calculate_gain(rx_antenna_bearing, rx_elev_angle);
+	
+	delete _TX_antenna;
+	delete _RX_antenna;
 	signal = link_budget - dbloss - clutter_loss + pol_loss;
 	double signal_strength_dbm = signal_strength - dbloss - clutter_loss + pol_loss;
 	double field_strength_uV = dbm_to_microvolt(signal_strength_dbm);
@@ -407,6 +424,8 @@ double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, i
 	_root_node->setDoubleValue("station[0]/field-strength-uV", field_strength_uV);
 	_root_node->setDoubleValue("station[0]/signal", signal);
 	_root_node->setDoubleValue("station[0]/tx-erp", tx_erp);
+	_root_node->setDoubleValue("station[0]/tx-pattern-gain", tx_pattern_gain);
+	_root_node->setDoubleValue("station[0]/rx-pattern-gain", rx_pattern_gain);
 	return signal;
 
 }

src/Radio/radio.hxx

@@ -28,7 +28,7 @@
 
 #include <simgear/math/sg_geodesy.hxx>
 #include <simgear/debug/logstream.hxx>
-
+#include "antenna.hxx"
 
 using std::string;
 
@@ -48,6 +48,8 @@ private:
 	double _tx_antenna_gain;
 	double _rx_line_losses;
 	double _tx_line_losses;
+	FGRadioAntenna* _TX_antenna;
+	FGRadioAntenna* _RX_antenna;
 	double _terrain_sampling_distance;
 	int _polarization;
 	std::map<string, double[2]> _mat_database;