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/navlist.hxx>
19 * Start by calculating the radar horizon based on the elevation
20 * difference, then clamp to the maximum, then add a fudge for
21 * borderline reception.
24 adjust_range (double transmitter_elevation_ft, double aircraft_altitude_ft,
27 double delta_elevation_ft =
28 fabs(aircraft_altitude_ft - transmitter_elevation_ft);
29 double range_nm = 1.23 * sqrt(delta_elevation_ft);
30 if (range_nm > max_range_nm)
31 range_nm = max_range_nm;
32 else if (range_nm < 20.0)
34 double rand = sg_random();
35 return range_nm + (range_nm * rand * rand);
39 DME::DME ( SGPropertyNode *node )
40 : _last_distance_nm(0),
41 _last_frequency_mhz(-1),
42 _time_before_search_sec(0),
43 _transmitter_valid(false),
44 _transmitter_elevation_ft(0),
45 _transmitter_range_nm(0),
46 _transmitter_bias(0.0),
51 for ( i = 0; i < node->nChildren(); ++i ) {
52 SGPropertyNode *child = node->getChild(i);
53 string cname = child->getName();
54 string cval = child->getStringValue();
55 if ( cname == "name" ) {
57 } else if ( cname == "number" ) {
58 num = child->getIntValue();
60 SG_LOG( SG_INSTR, SG_WARN, "Error in dme config logic" );
61 if ( name.length() ) {
62 SG_LOG( SG_INSTR, SG_WARN, "Section = " << name );
69 : _last_distance_nm(0),
70 _last_frequency_mhz(-1),
71 _time_before_search_sec(0),
72 _transmitter_valid(false),
73 _transmitter_elevation_ft(0),
74 _transmitter_range_nm(0),
75 _transmitter_bias(0.0)
87 branch = "/instrumentation/" + name;
89 SGPropertyNode *node = fgGetNode(branch.c_str(), num, true );
91 _longitude_node = fgGetNode("/position/longitude-deg", true);
92 _latitude_node = fgGetNode("/position/latitude-deg", true);
93 _altitude_node = fgGetNode("/position/altitude-ft", true);
94 _serviceable_node = node->getChild("serviceable", 0, true);
95 _electrical_node = fgGetNode("/systems/electrical/outputs/dme", true);
96 SGPropertyNode *fnode = node->getChild("frequencies", 0, true);
97 _source_node = fnode->getChild("source", 0, true);
98 _frequency_node = fnode->getChild("selected-mhz", 0, true);
99 _in_range_node = node->getChild("in-range", 0, true);
100 _distance_node = node->getChild("indicated-distance-nm", 0, true);
101 _speed_node = node->getChild("indicated-ground-speed-kt", 0, true);
102 _time_node = node->getChild("indicated-time-min", 0, true);
106 DME::update (double delta_time_sec)
108 // Figure out the source
109 const char * source = _source_node->getStringValue();
110 if (source[0] == '\0') {
112 branch = "/instrumentation/" + name + "/frequencies/selected-mhz";
113 _source_node->setStringValue(branch.c_str());
114 source = _source_node->getStringValue();
118 double frequency_mhz = fgGetDouble(source, 108.0);
119 if (frequency_mhz != _last_frequency_mhz) {
120 _time_before_search_sec = 0;
121 _last_frequency_mhz = frequency_mhz;
124 // Get the aircraft position
125 double longitude_rad =
126 _longitude_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
127 double latitude_rad =
128 _latitude_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
130 _altitude_node->getDoubleValue() * SG_FEET_TO_METER;
132 // On timeout, scan again
133 _time_before_search_sec -= delta_time_sec;
134 if (_time_before_search_sec < 0)
135 search(frequency_mhz, longitude_rad,
136 latitude_rad, altitude_m);
138 // If it's off, don't bother.
139 if (!_serviceable_node->getBoolValue() ||
140 !_electrical_node->getBoolValue() ||
141 !_transmitter_valid) {
142 _last_distance_nm = 0;
143 _in_range_node->setBoolValue(false);
144 _distance_node->setDoubleValue(0);
145 _speed_node->setDoubleValue(0);
146 _time_node->setDoubleValue(0);
150 // Calculate the distance to the transmitter
152 sgGeodToCart(Point3D(longitude_rad, latitude_rad, altitude_m));
153 double distance_nm = _transmitter.distance3D(location) * SG_METER_TO_NM;
155 double range_nm = adjust_range(_transmitter_elevation_ft,
156 altitude_m * SG_METER_TO_FEET,
157 _transmitter_range_nm);
159 if (distance_nm <= range_nm) {
160 double speed_kt = (fabs(distance_nm - _last_distance_nm) *
161 ((1 / delta_time_sec) * 3600.0));
162 _last_distance_nm = distance_nm;
164 _in_range_node->setBoolValue(true);
165 double tmp_dist = distance_nm - _transmitter_bias;
166 if ( tmp_dist < 0.0 ) {
169 _distance_node->setDoubleValue( tmp_dist );
170 _speed_node->setDoubleValue(speed_kt);
171 _time_node->setDoubleValue(distance_nm/speed_kt*60.0);
174 _last_distance_nm = 0;
175 _in_range_node->setBoolValue(false);
176 _distance_node->setDoubleValue(0);
177 _speed_node->setDoubleValue(0);
178 _time_node->setDoubleValue(0);
183 DME::search (double frequency_mhz, double longitude_rad,
184 double latitude_rad, double altitude_m)
187 _time_before_search_sec = 1.0;
189 // try the ILS list first
191 = globals->get_dmelist()->findByFreq( frequency_mhz, longitude_rad,
192 latitude_rad, altitude_m);
194 _transmitter_valid = (dme != NULL);
196 if ( _transmitter_valid ) {
197 _transmitter = Point3D(dme->get_x(), dme->get_y(), dme->get_z());
198 _transmitter_elevation_ft = dme->get_elev_ft();
199 _transmitter_range_nm = dme->get_range();
200 _transmitter_bias = dme->get_multiuse();