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.
10 #include <simgear/compiler.h>
11 #include <simgear/math/sg_geodesy.hxx>
12 #include <simgear/math/sg_random.h>
14 #include <Main/fg_props.hxx>
15 #include <Navaids/navlist.hxx>
23 * Start by calculating the radar horizon based on the elevation
24 * difference, then clamp to the maximum, then add a fudge for
25 * borderline reception.
28 adjust_range (double transmitter_elevation_ft, double aircraft_altitude_ft,
31 double delta_elevation_ft =
32 fabs(aircraft_altitude_ft - transmitter_elevation_ft);
33 double range_nm = 1.23 * sqrt(delta_elevation_ft);
34 if (range_nm > max_range_nm)
35 range_nm = max_range_nm;
36 else if (range_nm < 20.0)
38 double rand = sg_random();
39 return range_nm + (range_nm * rand * rand);
43 DME::DME ( SGPropertyNode *node )
44 : _last_distance_nm(0),
45 _last_frequency_mhz(-1),
46 _time_before_search_sec(0),
47 _transmitter_valid(false),
48 _transmitter_elevation_ft(0),
49 _transmitter_range_nm(0),
50 _transmitter_bias(0.0),
55 for ( i = 0; i < node->nChildren(); ++i ) {
56 SGPropertyNode *child = node->getChild(i);
57 string cname = child->getName();
58 string cval = child->getStringValue();
59 if ( cname == "name" ) {
61 } else if ( cname == "number" ) {
62 num = child->getIntValue();
64 SG_LOG( SG_INSTR, SG_WARN, "Error in dme config logic" );
65 if ( name.length() ) {
66 SG_LOG( SG_INSTR, SG_WARN, "Section = " << name );
73 : _last_distance_nm(0),
74 _last_frequency_mhz(-1),
75 _time_before_search_sec(0),
76 _transmitter_valid(false),
77 _transmitter_elevation_ft(0),
78 _transmitter_range_nm(0),
79 _transmitter_bias(0.0)
91 branch = "/instrumentation/" + name;
93 SGPropertyNode *node = fgGetNode(branch.c_str(), num, true );
95 _longitude_node = fgGetNode("/position/longitude-deg", true);
96 _latitude_node = fgGetNode("/position/latitude-deg", true);
97 _altitude_node = fgGetNode("/position/altitude-ft", true);
98 _serviceable_node = node->getChild("serviceable", 0, true);
99 _electrical_node = fgGetNode("/systems/electrical/outputs/dme", true);
100 SGPropertyNode *fnode = node->getChild("frequencies", 0, true);
101 _source_node = fnode->getChild("source", 0, true);
102 _frequency_node = fnode->getChild("selected-mhz", 0, true);
103 _in_range_node = node->getChild("in-range", 0, true);
104 _distance_node = node->getChild("indicated-distance-nm", 0, true);
105 _speed_node = node->getChild("indicated-ground-speed-kt", 0, true);
106 _time_node = node->getChild("indicated-time-min", 0, true);
110 DME::update (double delta_time_sec)
112 // Figure out the source
113 const char * source = _source_node->getStringValue();
114 if (source[0] == '\0') {
116 branch = "/instrumentation/" + name + "/frequencies/selected-mhz";
117 _source_node->setStringValue(branch.c_str());
118 source = _source_node->getStringValue();
122 double frequency_mhz = fgGetDouble(source, 108.0);
123 if (frequency_mhz != _last_frequency_mhz) {
124 _time_before_search_sec = 0;
125 _last_frequency_mhz = frequency_mhz;
128 // Get the aircraft position
129 double longitude_rad =
130 _longitude_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
131 double latitude_rad =
132 _latitude_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
134 _altitude_node->getDoubleValue() * SG_FEET_TO_METER;
136 // On timeout, scan again
137 _time_before_search_sec -= delta_time_sec;
138 if (_time_before_search_sec < 0)
139 search(frequency_mhz, longitude_rad,
140 latitude_rad, altitude_m);
142 // If it's off, don't bother.
143 if (!_serviceable_node->getBoolValue() ||
144 !_electrical_node->getBoolValue() ||
145 !_transmitter_valid) {
146 _last_distance_nm = 0;
147 _in_range_node->setBoolValue(false);
148 _distance_node->setDoubleValue(0);
149 _speed_node->setDoubleValue(0);
150 _time_node->setDoubleValue(0);
154 // Calculate the distance to the transmitter
155 SGGeod geod = SGGeod::fromRadM(longitude_rad, latitude_rad, altitude_m);
156 SGVec3d location = SGVec3d::fromGeod(geod);
158 double distance_nm = dist(_transmitter, location) * SG_METER_TO_NM;
160 double range_nm = adjust_range(_transmitter_elevation_ft,
161 altitude_m * SG_METER_TO_FEET,
162 _transmitter_range_nm);
164 if (distance_nm <= range_nm) {
165 double speed_kt = (fabs(distance_nm - _last_distance_nm) *
166 ((1 / delta_time_sec) * 3600.0));
167 _last_distance_nm = distance_nm;
169 _in_range_node->setBoolValue(true);
170 double tmp_dist = distance_nm - _transmitter_bias;
171 if ( tmp_dist < 0.0 ) {
174 _distance_node->setDoubleValue( tmp_dist );
175 _speed_node->setDoubleValue(speed_kt);
176 _time_node->setDoubleValue(distance_nm/speed_kt*60.0);
179 _last_distance_nm = 0;
180 _in_range_node->setBoolValue(false);
181 _distance_node->setDoubleValue(0);
182 _speed_node->setDoubleValue(0);
183 _time_node->setDoubleValue(0);
188 DME::search (double frequency_mhz, double longitude_rad,
189 double latitude_rad, double altitude_m)
192 _time_before_search_sec = 1.0;
194 // try the ILS list first
196 = globals->get_dmelist()->findByFreq( frequency_mhz, longitude_rad,
197 latitude_rad, altitude_m);
199 _transmitter_valid = (dme != NULL);
201 if ( _transmitter_valid ) {
202 _transmitter = dme->get_cart();
203 _transmitter_elevation_ft = dme->get_elev_ft();
204 _transmitter_range_nm = dme->get_range();
205 _transmitter_bias = dme->get_multiuse();