Add function to calculate polarization loss

This function is reliable only for vertical polarization

src/Radio/CMakeLists.txt

@@ -1,11 +1,13 @@
 include(FlightGearComponent)
 
 set(SOURCES
+	antenna.cxx
 	radio.cxx
 	itm.cpp
 	)
 
 set(HEADERS
+	antenna.hxx
 	radio.hxx
 	)
 

src/Radio/antenna.cxx

@@ -15,3 +15,37 @@
 // You should have received a copy of the GNU General Public License
 // along with this program; if not, write to the Free Software
 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+
+#ifdef HAVE_CONFIG_H
+#  include <config.h>
+#endif
+
+#include <math.h>
+
+#include <stdlib.h>
+
+#include <Scenery/scenery.hxx>
+#include "antenna.hxx"
+
+
+FGRadioAntenna::FGRadioAntenna() {
+	
+	_mirror_y = 1;
+	_mirror_z = 1;
+}
+
+FGRadioAntenna::~FGRadioAntenna() {
+	
+}
+
+double FGRadioAntenna::calculate_gain(double azimuth, double theta) {
+	return 0;
+}
+
+
+
+
+void FGRadioAntenna::_load_antenna_pattern() {
+	
+}

src/Radio/antenna.hxx

@@ -15,3 +15,39 @@
 // You should have received a copy of the GNU General Public License
 // along with this program; if not, write to the Free Software
 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+#ifndef __cplusplus
+# error This library requires C++
+#endif
+
+#include <simgear/compiler.h>
+#include <simgear/structure/subsystem_mgr.hxx>
+#include <Main/fg_props.hxx>
+
+#include <simgear/math/sg_geodesy.hxx>
+#include <simgear/debug/logstream.hxx>
+
+class FGRadioAntenna
+{
+private:
+	void _load_antenna_pattern();
+	int _mirror_y;
+	int _mirror_z;
+	double _heading;
+	struct AntennaGain {
+		double azimuth;
+		double elevation_angle;
+		double gain;
+	};
+	
+	typedef std::vector<AntennaGain> AntennaPattern;
+	AntennaPattern _pattern;
+	
+public:
+	
+	FGRadioAntenna();
+    ~FGRadioAntenna();
+	double calculate_gain(double azimuth, double theta);
+	
+	
+};

src/Radio/radio.cxx

@@ -357,13 +357,6 @@ double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, i
 	}
 	
 	
-	double max_alt_between=0.0;
-	for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
-		if (_elevations[i] > max_alt_between) {
-			max_alt_between = _elevations[i];
-		}
-	}
-	
 	double num_points= (double)_elevations.size();
 
 	_elevations.push_front(point_distance);
@@ -875,4 +868,23 @@ double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, i
 	
 }
 
+/*** calculate loss due to polarization mismatch
+*	this function is only reliable for vertical polarization
+*	due to the V-shape of horizontally polarized antennas
+***/
+double FGRadioTransmission::polarization_loss() {
+	
+	double theta_deg;
+	double roll = fgGetDouble("/orientation/roll-deg");
+	double pitch = fgGetDouble("/orientation/pitch-deg");
+	double theta = acos( sqrt( cos(roll) * cos(roll) + cos(pitch) * cos(pitch) ));
+	if (_polarization == 1)
+		theta_deg = 90.0 - theta;
+	else
+		theta_deg = theta;
+	if (fabs(theta_deg) > 85.0)	// we don't want to converge into infinity
+		theta_deg = 85.0;
+	return 10 * log10(cos(theta_deg) * cos(theta_deg));
+}
+
 

src/Radio/radio.hxx

@@ -53,6 +53,7 @@ private:
 	std::map<string, double[2]> _mat_database;
 	
 	int _propagation_model; /// 0 none, 1 round Earth, 2 ITM
+	double polarization_loss();
 	double ITM_calculate_attenuation(SGGeod tx_pos, double freq, int ground_to_air);
 	double LOS_calculate_attenuation(SGGeod tx_pos, double freq, int ground_to_air);
 	void clutterLoss(double freq, double distance_m, double itm_elev[], std::deque<string> materials,