flightgear/src/Instrumentation/tacan.cxx

// tacan.cxx - Tactical Navigation Beacon.
// Written by Vivian Meazaa, started 2005.
//
// This file is in the Public Domain and comes with no warranty.

#include <simgear/compiler.h>
#include <simgear/math/sg_geodesy.hxx>
#include <simgear/math/sg_random.h>

#include <Main/fg_props.hxx>
#include <Navaids/navlist.hxx>

#include "tacan.hxx"


/**
 * Adjust the range.
 *
 * Start by calculating the radar horizon based on the elevation
 * difference, then clamp to the maximum, then add a fudge for
 * borderline reception.
 */
static double
adjust_range (double transmitter_elevation_ft, double aircraft_altitude_ft,
              double max_range_nm)
{
    max_range_nm = 150;
    double delta_elevation_ft =
        fabs(aircraft_altitude_ft - transmitter_elevation_ft);
    double range_nm = 1.23 * sqrt(delta_elevation_ft);
    if (range_nm > max_range_nm)
        range_nm = max_range_nm;
    else if (range_nm < 20.0)
        range_nm = 20.0;
    double rand = sg_random();
    SG_LOG( SG_INSTR, SG_DEBUG, " tacan range " << range_nm << " max range " << max_range_nm);
    return range_nm + (range_nm * rand * rand);
}


TACAN::TACAN ( SGPropertyNode *node )
    : _last_distance_nm(0),
      _last_frequency_mhz(-1),
      _time_before_search_sec(0),
      _carrier_valid(false),
      _transmitter_valid(false),
      _transmitter_elevation_ft(0),
      _transmitter_range_nm(0),
      _transmitter_bias(0.0),
      
      name("tacan"),
      num(0)
{
    
    int i;
    for ( i = 0; i < node->nChildren(); ++i ) {
        SGPropertyNode *child = node->getChild(i);
        string cname = child->getName();
        string cval = child->getStringValue();
        if ( cname == "name" ) {
            name = cval;
        } else if ( cname == "number" ) {
            num = child->getIntValue();
        } else {
            SG_LOG( SG_INSTR, SG_DEBUG, "Error in TACAN config logic" );
            if ( name.length() ) {
                SG_LOG( SG_INSTR, SG_DEBUG, "Section = " << name );
            }
        }
    }
}

TACAN::TACAN ()
    : _last_distance_nm(0),
      _last_frequency_mhz(-1),
      _time_before_search_sec(0),
      _carrier_valid(false),
      _transmitter_valid(false),
      _transmitter_elevation_ft(0),
      _transmitter_range_nm(0),
      _transmitter_bearing_deg(0),
      _transmitter_bias(0.0),
      _transmitter_name(""),
      name("tacan")
{
}

TACAN::~TACAN ()
{
}

void
TACAN::init ()
{
    string branch;
    branch = "/instrumentation/" + name;

    SGPropertyNode *node = fgGetNode(branch.c_str(), num, true );

    _longitude_node = fgGetNode("/position/longitude-deg", true);
    _latitude_node = fgGetNode("/position/latitude-deg", true);
    _altitude_node = fgGetNode("/position/altitude-ft", true);
    _serviceable_node = node->getChild("serviceable", 0, true);
    _electrical_node = fgGetNode("/systems/electrical/outputs/tacan", true);
    SGPropertyNode *fnode = node->getChild("frequencies", 0, true);
    _source_node = fnode->getChild("source", 0, true);
    _frequency_node = fnode->getChild("selected-mhz", 0, true);
    _channel_node = fnode->getChild("selected-channel", 1, true);
    _channel_node = fnode->getChild("selected-channel", 2, true);
    _channel_node = fnode->getChild("selected-channel", 3, true);
    _channel_node = fnode->getChild("selected-channel", 4, true);
    _in_range_node = node->getChild("in-range", 0, true);
    _distance_node = node->getChild("indicated-distance-nm", 0, true);
    _speed_node = node->getChild("indicated-ground-speed-kt", 0, true);
    _time_node = node->getChild("indicated-time-min", 0, true);
    _name_node = node->getChild("name", 0, true);
    _bearing_node = node->getChild("indicated-bearing-true-deg", 0, true);
    _carrier_lat_node = fgGetNode("/ai/models/carrier/position/latitude-deg", true);
    _carrier_lon_node = fgGetNode("/ai/models/carrier/position/longitude-deg", true);
    _carrier_name_node = fgGetNode("/ai/models/carrier/name", true);
   
}

void
TACAN::update (double delta_time_sec)
{   
    double az2 = 0; 
    double bearing = 0;
    double distance = 0; 
    double carrier_az2= 0; 
    double carrier_bearing = 0; 
    double carrier_distance = 0;
    double frequency_mhz = 0;
    string _channel, _last_channel, _channel_1, _channel_2,_channel_3, _channel_4;

                                // If it's off, don't waste any time.    
    if (!_serviceable_node->getBoolValue() ||
        !_electrical_node->getBoolValue() 
        ) {
            _last_distance_nm = 0;
            _in_range_node->setBoolValue(false);
            _distance_node->setDoubleValue(0);
            _speed_node->setDoubleValue(0);
            _time_node->setDoubleValue(0);
            SG_LOG( SG_INSTR, SG_DEBUG, "skip tacan "  );
            return;
    }else{
        //SG_LOG( SG_INSTR, SG_DEBUG, "run tacan "  );
        }    
                                
                                // Figure out the source
    const char * source = _source_node->getStringValue();
   
    if (source[0] == '\0') {
        string branch;
        branch = "/instrumentation/" + name + "/frequencies/selected-channel";
      //  branch = "/instrumentation/" + _name + "/frequencies/selected-mhz";      
        _source_node->setStringValue(branch.c_str());
        source = _source_node->getStringValue();
        SG_LOG( SG_INSTR, SG_DEBUG, "source " << source  ); 
    }
                                // Get the channel   
    _channel_1 = fgGetString("/instrumentation/tacan/frequencies/selected-channel[1]");
    _channel_2 = fgGetString("/instrumentation/tacan/frequencies/selected-channel[2]");
    _channel_3 = fgGetString("/instrumentation/tacan/frequencies/selected-channel[3]");
    _channel_4 = fgGetString("/instrumentation/tacan/frequencies/selected-channel[4]");
    SG_LOG( SG_INSTR, SG_DEBUG, "channels " << _channel_1 << _channel_2 << _channel_3 << _channel_4);
    _channel = _channel_1 + _channel_2 + _channel_3 + _channel_4;
    SG_LOG( SG_INSTR, SG_DEBUG, "channel " << _channel );
    
                                // Get the frequecncy
    if (_channel != _last_channel) {
        _time_before_search_sec = 0;
        _last_channel = _channel;
        frequency_mhz = searchChannel(_channel);
        SG_LOG( SG_INSTR, SG_DEBUG, "frequency " << frequency_mhz );
        _frequency_node->setDoubleValue(frequency_mhz);
    }        
        
                                // Get the aircraft position
     double longitude_deg = _longitude_node->getDoubleValue();
     double latitude_deg  = _latitude_node->getDoubleValue();
     double altitude_m    = _altitude_node->getDoubleValue() * SG_FEET_TO_METER;
     double longitude_rad = longitude_deg * SGD_DEGREES_TO_RADIANS;
     double latitude_rad  = latitude_deg * SGD_DEGREES_TO_RADIANS;
                                          
                                // On timeout, scan again
    _time_before_search_sec -= delta_time_sec;
    if (_time_before_search_sec < 0 && frequency_mhz > 0)
        search(frequency_mhz, longitude_rad,
               latitude_rad, altitude_m);

                                 // Calculate the distance to the transmitter
                                 
     //calculate the bearing and range of the carrier from the aircraft
     SG_LOG( SG_INSTR, SG_DEBUG, "carrier_lat " << _carrier_lat);
     SG_LOG( SG_INSTR, SG_DEBUG, "carrier_lon " << _carrier_lon);
     SG_LOG( SG_INSTR, SG_DEBUG, "carrier_name " << _carrier_name);
     SG_LOG( SG_INSTR, SG_DEBUG, "carrier_valid " << _carrier_valid);
     geo_inverse_wgs_84(altitude_m,
                        latitude_deg,
                        longitude_deg,
                        _carrier_lat,
                        _carrier_lon,
                        &carrier_bearing, &carrier_az2, &carrier_distance);
                         
      
     //calculate the bearing and range of the station from the aircraft
     geo_inverse_wgs_84(altitude_m,
                        latitude_deg,
                        longitude_deg,
                        _transmitter_lat,
                        _transmitter_lon,
                        &bearing, &az2, &distance);
    
                     
     //select the nearer
     if ( carrier_distance <= distance && _carrier_valid) { 
         SG_LOG( SG_INSTR, SG_DEBUG, "carrier_distance_nm " << carrier_distance);
         SG_LOG( SG_INSTR, SG_DEBUG, "distance_nm " << distance);
         bearing = carrier_bearing;
         distance = carrier_distance;
         _transmitter_elevation_ft = _carrier_elevation_ft;
         _transmitter_range_nm = _carrier_range_nm;
         _transmitter_bias = _carrier_bias;
         _transmitter_name = _carrier_name;
         _name_node->setStringValue(_transmitter_name.c_str());
     }    
               
     double distance_nm = distance * SG_METER_TO_NM;        
     SG_LOG( SG_INSTR, SG_DEBUG, "distance_nm " << distance_nm  << " bearing " << bearing);                          

    /*Point3D location =
        sgGeodToCart(Point3D(longitude_rad, latitude_rad, altitude_m));
    double distance_nm = _transmitter.distance3D(location) * SG_METER_TO_NM;*/

    double range_nm = adjust_range(_transmitter_elevation_ft,
                                   altitude_m * SG_METER_TO_FEET,
                                   _transmitter_range_nm);

    if (distance_nm <= range_nm) {
        double speed_kt = (fabs(distance_nm - _last_distance_nm) *
                           ((1 / delta_time_sec) * 3600.0));
        _last_distance_nm = distance_nm;

        _in_range_node->setBoolValue(true);
        double tmp_dist = distance_nm - _transmitter_bias;
        if ( tmp_dist < 0.0 ) {
            tmp_dist = 0.0;
        }
        _distance_node->setDoubleValue( tmp_dist );
        _speed_node->setDoubleValue(speed_kt);
        _time_node->setDoubleValue(distance_nm/speed_kt*60.0);
        _bearing_node->setDoubleValue(bearing);
        
    } else {
        _last_distance_nm = 0;
        _in_range_node->setBoolValue(false);
        _distance_node->setDoubleValue(0);
        _speed_node->setDoubleValue(0);
        _time_node->setDoubleValue(0);
        _bearing_node->setDoubleValue(0);
    }
    
                                // If we can't find a valid station set everything to zero
    if (!_transmitter_valid && !_carrier_valid)
    {
        _in_range_node->setBoolValue(false);
        _distance_node->setDoubleValue(0);
        _speed_node->setDoubleValue(0);
        _time_node->setDoubleValue(0);
        _bearing_node->setDoubleValue(0);
        _transmitter_name = "";
        _name_node->setStringValue(_transmitter_name.c_str());
        return;
    }
} // end function update

void
TACAN::search (double frequency_mhz, double longitude_rad,
             double latitude_rad, double altitude_m)
{    
    
    SG_LOG( SG_INSTR, SG_DEBUG, "tacan freq " << frequency_mhz );
     
    // reset search time
    _time_before_search_sec = 1.0;
    
    //try any carriers first
     FGNavRecord *carrier_tacan
          = globals->get_carrierlist()->findStationByFreq( frequency_mhz );
    _carrier_valid = (carrier_tacan != NULL);

    if ( _carrier_valid ) {
        SG_LOG( SG_INSTR, SG_DEBUG, "carrier transmitter valid " << _carrier_valid  );
         
        string str1( carrier_tacan->get_name() );
        string str2 ( _carrier_name_node->getStringValue());
        SG_LOG( SG_INSTR, SG_DEBUG, "strings 1 " << str1 << " 2 " << str2 );
        unsigned int loc1= str1.find( str2, 0 );
          if( loc1 != string::npos && str2 != "" ){
              SG_LOG( SG_INSTR, SG_DEBUG, " string found" );
              _carrier_lat = _carrier_lat_node->getDoubleValue();
              _carrier_lon = _carrier_lon_node->getDoubleValue();
              _carrier_elevation_ft = carrier_tacan->get_elev_ft();
              _carrier_range_nm = carrier_tacan->get_range();
              _carrier_bias = carrier_tacan->get_multiuse();
              _carrier_name = carrier_tacan->get_name();
              }
          else{
              _carrier_valid = 0;
              SG_LOG( SG_INSTR, SG_DEBUG, " carrier transmitter invalid " << _carrier_valid );
          }    
              
              
        //_name_node->setStringValue(_transmitter_name.c_str());
        
        SG_LOG( SG_INSTR, SG_DEBUG, "lat " << _carrier_lat << "lon " << _carrier_lon);
        SG_LOG( SG_INSTR, SG_DEBUG, "elev " << _carrier_elevation_ft);
        SG_LOG( SG_INSTR, SG_DEBUG, "name " << _carrier_name);
        
    } else {
         SG_LOG( SG_INSTR, SG_DEBUG, " carrier transmitter invalid " << _carrier_valid  );
     }    
    

    // try the TACAN/VORTAC list next
    FGNavRecord *tacan
        = globals->get_tacanlist()->findByFreq( frequency_mhz, longitude_rad,
                                              latitude_rad, altitude_m);

    _transmitter_valid = (tacan != NULL);

    if ( _transmitter_valid ) {
        SG_LOG( SG_INSTR, SG_DEBUG, "transmitter valid " << _transmitter_valid  );
       
        _transmitter_lat = tacan->get_lat();
        _transmitter_lon = tacan->get_lon();
        _transmitter_elevation_ft = tacan->get_elev_ft();
        _transmitter_range_nm = tacan->get_range();
        _transmitter_bias = tacan->get_multiuse();
        _transmitter_name = tacan->get_name();
        _name_node->setStringValue(_transmitter_name.c_str());
        
        SG_LOG( SG_INSTR, SG_DEBUG, "lat " << _transmitter_lat << "lon " << _transmitter_lon);
        SG_LOG( SG_INSTR, SG_DEBUG, "elev " << _transmitter_elevation_ft);
        SG_LOG( SG_INSTR, SG_DEBUG, "name " << _transmitter_name);
        
    } else {
         SG_LOG( SG_INSTR, SG_DEBUG, "transmitter invalid " << _transmitter_valid  );
     }    
        
}

double
TACAN::searchChannel (string _channel){
    
    double frequency_khz = 0;
    
    FGTACANRecord *freq
        = globals->get_channellist()->findByChannel( _channel );
    double _freq_valid = (freq != NULL); 
    SG_LOG( SG_INSTR, SG_DEBUG, "freq valid " << _freq_valid  );
    if ( _freq_valid ) {
        frequency_khz = freq->get_freq();
        SG_LOG( SG_INSTR, SG_DEBUG, "freq output " << frequency_khz  );
        //check sanity
        if (frequency_khz >9620 and  frequency_khz <= 12130)return frequency_khz/100;
    }
    return frequency_khz = 0;
} // end TACAN::searchChannel
   
// end of TACAN.cxx