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)
57 _longitude_node = fgGetNode("/position/longitude-deg", true);
58 _latitude_node = fgGetNode("/position/latitude-deg", true);
59 _altitude_node = fgGetNode("/position/altitude-ft", true);
60 _serviceable_node = fgGetNode("/instrumentation/dme/serviceable", true);
61 _electrical_node = fgGetNode("/systems/electrical/outputs/dme", true);
62 _source_node = fgGetNode("/instrumentation/dme/frequencies/source", true);
64 fgGetNode("/instrumentation/dme/frequencies/selected-mhz", true);
66 _in_range_node = fgGetNode("/instrumentation/dme/in-range", true);
68 fgGetNode("/instrumentation/dme/indicated-distance-nm", true);
70 fgGetNode("/instrumentation/dme/indicated-ground-speed-kt", true);
72 fgGetNode("/instrumentation/dme/indicated-time-min", true);
76 DME::update (double delta_time_sec)
78 // Figure out the source
79 const char * source = _source_node->getStringValue();
80 if (source[0] == '\0') {
81 source = "/instrumentation/dme/frequencies/selected-mhz";
82 _source_node->setStringValue(source);
86 double frequency_mhz = fgGetDouble(source, 108.0);
87 if (frequency_mhz != _last_frequency_mhz) {
88 _time_before_search_sec = 0;
89 _last_frequency_mhz = frequency_mhz;
92 // Get the aircraft position
93 double longitude_rad =
94 _longitude_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
96 _latitude_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
98 _altitude_node->getDoubleValue() * SG_FEET_TO_METER;
100 // On timeout, scan again
101 _time_before_search_sec -= delta_time_sec;
102 if (_time_before_search_sec < 0)
103 search(frequency_mhz, longitude_rad,
104 latitude_rad, altitude_m);
106 // If it's off, don't bother.
107 if (!_serviceable_node->getBoolValue() ||
108 !_electrical_node->getBoolValue() ||
109 !_transmitter_valid) {
110 _last_distance_nm = 0;
111 _in_range_node->setBoolValue(false);
112 _distance_node->setDoubleValue(0);
113 _speed_node->setDoubleValue(0);
114 _time_node->setDoubleValue(0);
118 // Calculate the distance to the transmitter
120 sgGeodToCart(Point3D(longitude_rad, latitude_rad, altitude_m));
121 double distance_nm = _transmitter.distance3D(location) * SG_METER_TO_NM;
122 double range_nm = adjust_range(_transmitter_elevation_ft,
123 altitude_m * SG_METER_TO_FEET,
124 _transmitter_range_nm);
125 if (distance_nm <= range_nm) {
126 double speed_kt = (fabs(distance_nm - _last_distance_nm) *
127 ((1 / delta_time_sec) * 3600.0));
128 _last_distance_nm = distance_nm;
130 _in_range_node->setBoolValue(true);
131 _distance_node->setDoubleValue(distance_nm);
132 _speed_node->setDoubleValue(speed_kt);
133 _time_node->setDoubleValue(distance_nm/speed_kt*60.0);
136 _last_distance_nm = 0;
137 _in_range_node->setBoolValue(false);
138 _distance_node->setDoubleValue(0);
139 _speed_node->setDoubleValue(0);
140 _time_node->setDoubleValue(0);
145 DME::search (double frequency_mhz, double longitude_rad,
146 double latitude_rad, double altitude_m)
149 _time_before_search_sec = 1.0;
151 // try the ILS list first
152 FGILS * ils = current_ilslist->findByFreq(frequency_mhz,
156 if (ils !=0 && ils->get_has_dme()) {
157 _transmitter_valid = true;
158 _transmitter = Point3D(ils->get_dme_x(),
161 _transmitter_elevation_ft = ils->get_gselev() * SG_METER_TO_FEET;
162 _transmitter_range_nm = 50; // arbitrary
167 FGNav * nav = current_navlist->findByFreq(frequency_mhz,
171 if (nav != 0 && nav->get_has_dme()) {
172 _transmitter_valid = true;
173 _transmitter = Point3D(nav->get_x(),
176 _transmitter_elevation_ft = nav->get_elev() * SG_METER_TO_FEET;
177 _transmitter_range_nm = nav->get_range(); // fixme
181 _transmitter_valid = false;