antenna.cxx

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// antenna.cxx -- implementation of FGRadioAntenna
// Class to represent a virtual radio antenna properties
// Written by Adrian Musceac YO8RZZ, started December 2011.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// 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 <cmath>
#include <iostream>
#include <stdlib.h>
#include <fstream>
#include <Scenery/scenery.hxx>
#include <simgear/io/iostreams/sgstream.hxx>
 
#include "antenna.hxx"
 
using namespace std;
 
FGRadioAntenna::FGRadioAntenna(string type) {
 
        _mirror_y = 1;  // normally we want to mirror these axis because the pattern is simetric
        _mirror_z = 1;
        _invert_ground = 0;             // TODO: use for inverting the antenna ground, for instance aircraft body reflection
        load_NEC_antenna_pattern(type);
}
 
FGRadioAntenna::~FGRadioAntenna() {
        for (unsigned i =0; i < _pattern.size(); i++) {
                AntennaGain *point_gain = _pattern[i];
                delete point_gain;
        }
        _pattern.clear();
}
 
// WIP
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;
        //cerr << "Bearing: " << bearing << " angle: " << angle << " azimuth: " << azimuth << " elevation: " << elevation << endl;
        for (unsigned 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;
}
 
 
void FGRadioAntenna::load_NEC_antenna_pattern(string type) {
 
        //SGPath pattern_file(globals->get_fg_home());
        SGPath pattern_file(globals->get_fg_root());
        pattern_file.append("Navaids/Antennas");
        pattern_file.append(type + ".txt");
        if (!pattern_file.exists()) {
                return;
        }
        sg_ifstream file_in(pattern_file);
        int heading, elevation;
        double gain;
        while(!file_in.eof()) {
                file_in >> heading >> elevation >> gain;
                if( (_mirror_y == 1) && (heading > 180) ) {
                        continue;
                }
                if ( (_mirror_z == 1) && (elevation < 0) ) {
                        continue;
                }
                //cerr << "head: " << heading << " elev: " << elevation << " gain: " << gain << endl;
                AntennaGain *datapoint = new AntennaGain;
                datapoint->azimuth = heading;
                datapoint->elevation = 90.0 - abs(elevation);
                datapoint->gain = gain;
                _pattern.push_back(datapoint);
        }
}