1 // dme.cxx - distance-measuring equipment.
2 // Written by David Megginson, started 2003.
4 // This file is in the Public Domain and comes with no warranty.
6 #include <simgear/compiler.h>
7 #include <simgear/math/sg_geodesy.hxx>
8 #include <simgear/math/sg_random.h>
10 #include <Main/fg_props.hxx>
11 #include <Navaids/ilslist.hxx>
12 #include <Navaids/navlist.hxx>
20 * Start by calculating the radar horizon based on the elevation
21 * difference, then clamp to the maximum, then add a fudge for
22 * borderline reception.
25 adjust_range (double transmitter_elevation_ft, double aircraft_altitude_ft,
28 double delta_elevation_ft =
29 fabs(aircraft_altitude_ft - transmitter_elevation_ft);
30 double range_nm = 1.23 * sqrt(delta_elevation_ft);
31 if (range_nm > max_range_nm)
32 range_nm = max_range_nm;
33 else if (range_nm < 20.0)
35 double rand = sg_random();
36 return range_nm + (range_nm * rand * rand);
41 : _last_distance_nm(0),
42 _last_frequency_mhz(-1),
43 _time_before_search_sec(0),
44 _transmitter_valid(false),
45 _transmitter_elevation_ft(0),
46 _transmitter_range_nm(0),
47 _transmitter_bias(0.0)
58 _longitude_node = fgGetNode("/position/longitude-deg", true);
59 _latitude_node = fgGetNode("/position/latitude-deg", true);
60 _altitude_node = fgGetNode("/position/altitude-ft", true);
61 _serviceable_node = fgGetNode("/instrumentation/dme/serviceable", true);
62 _electrical_node = fgGetNode("/systems/electrical/outputs/dme", true);
63 _source_node = fgGetNode("/instrumentation/dme/frequencies/source", true);
65 fgGetNode("/instrumentation/dme/frequencies/selected-mhz", true);
67 _in_range_node = fgGetNode("/instrumentation/dme/in-range", true);
69 fgGetNode("/instrumentation/dme/indicated-distance-nm", true);
71 fgGetNode("/instrumentation/dme/indicated-ground-speed-kt", true);
73 fgGetNode("/instrumentation/dme/indicated-time-min", true);
77 DME::update (double delta_time_sec)
79 // Figure out the source
80 const char * source = _source_node->getStringValue();
81 if (source[0] == '\0') {
82 source = "/instrumentation/dme/frequencies/selected-mhz";
83 _source_node->setStringValue(source);
87 double frequency_mhz = fgGetDouble(source, 108.0);
88 if (frequency_mhz != _last_frequency_mhz) {
89 _time_before_search_sec = 0;
90 _last_frequency_mhz = frequency_mhz;
93 // Get the aircraft position
94 double longitude_rad =
95 _longitude_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
97 _latitude_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
99 _altitude_node->getDoubleValue() * SG_FEET_TO_METER;
101 // On timeout, scan again
102 _time_before_search_sec -= delta_time_sec;
103 if (_time_before_search_sec < 0)
104 search(frequency_mhz, longitude_rad,
105 latitude_rad, altitude_m);
107 // If it's off, don't bother.
108 if (!_serviceable_node->getBoolValue() ||
109 !_electrical_node->getBoolValue() ||
110 !_transmitter_valid) {
111 _last_distance_nm = 0;
112 _in_range_node->setBoolValue(false);
113 _distance_node->setDoubleValue(0);
114 _speed_node->setDoubleValue(0);
115 _time_node->setDoubleValue(0);
119 // Calculate the distance to the transmitter
121 sgGeodToCart(Point3D(longitude_rad, latitude_rad, altitude_m));
122 double distance_nm = _transmitter.distance3D(location) * SG_METER_TO_NM;
123 double range_nm = adjust_range(_transmitter_elevation_ft,
124 altitude_m * SG_METER_TO_FEET,
125 _transmitter_range_nm);
126 if (distance_nm <= range_nm) {
127 double speed_kt = (fabs(distance_nm - _last_distance_nm) *
128 ((1 / delta_time_sec) * 3600.0));
129 _last_distance_nm = distance_nm;
131 _in_range_node->setBoolValue(true);
132 _distance_node->setDoubleValue(distance_nm - _transmitter_bias);
133 _speed_node->setDoubleValue(speed_kt);
134 _time_node->setDoubleValue(distance_nm/speed_kt*60.0);
137 _last_distance_nm = 0;
138 _in_range_node->setBoolValue(false);
139 _distance_node->setDoubleValue(0);
140 _speed_node->setDoubleValue(0);
141 _time_node->setDoubleValue(0);
146 DME::search (double frequency_mhz, double longitude_rad,
147 double latitude_rad, double altitude_m)
150 _time_before_search_sec = 1.0;
152 // try the ILS list first
154 = globals->get_dmelist()->findByFreq( frequency_mhz, longitude_rad,
155 latitude_rad, altitude_m);
157 _transmitter_valid = (dme != NULL);
159 if ( _transmitter_valid ) {
160 _transmitter = Point3D(dme->get_x(), dme->get_y(), dme->get_z());
161 _transmitter_elevation_ft = dme->get_elev_ft();
162 _transmitter_range_nm = dme->get_range();
163 _transmitter_bias = dme->get_multiuse();