diff --git a/src/Instrumentation/navradio.cxx b/src/Instrumentation/navradio.cxx index 5343281..4c28233 100644 --- a/src/Instrumentation/navradio.cxx +++ b/src/Instrumentation/navradio.cxx @@ -25,6 +25,8 @@ # include #endif +#include "navradio.hxx" + #include #include @@ -36,13 +38,28 @@ #include #include -#include "Navaids/navrecord.hxx" +#include + +#include #include #include
-#include "navradio.hxx" + using std::string; +// General-purpose sawtooth function. Graph looks like this: +// /\ . +// \/ +// Odd symmetry, inversion symmetry about the origin. +// Unit slope at the origin. +// Max 1, min -1, period 4. +// Two zero-crossings per period, one with + slope, one with - slope. +// Useful for false localizer courses. +static double sawtooth(double xx) +{ + return 4.0 * fabs(xx/4.0 + 0.25 - floor(xx/4.0 + 0.75)) - 1.0; +} + // Constructor FGNavRadio::FGNavRadio(SGPropertyNode *node) : lon_node(fgGetNode("/position/longitude-deg", true)), @@ -102,6 +119,7 @@ FGNavRadio::FGNavRadio(SGPropertyNode *node) : last_x(0.0), last_loc_dist(0.0), last_xtrack_error(0.0), + _localizerWidth(5.0), _name(node->getStringValue("name", "nav")), _num(node->getIntValue("number", 0)), _time_before_search_sec(-1.0) @@ -462,21 +480,24 @@ void FGNavRadio::updateReceiver(double dt) } // CDI deflection - double r = radial - target_radial; + double r = target_radial - radial; SG_NORMALIZE_RANGE(r, -180.0, 180.0); - if ( fabs(r) > 90.0 ) { - r = ( r<0.0 ? -r-180.0 : -r+180.0 ); - } - r = -r; // reverse, since radial is outbound - _cdiDeflection = r; if ( is_loc ) { - // According to Robin Peel, the ILS is 4x more - // sensitive than a vor - // http://www.allstar.fiu.edu/aero/ILS.htm confirms both the 4x sensitvity - // increase, and also the 'full-deflection is 10-degrees for a VOR' clamp - _cdiDeflection *= 4.0; - } + // The factor of 30.0 gives a period of 120 which gives us 3 cycles and six + // zeros i.e. six courses: one front course, one back course, and four + // false courses. Three of the six are reverse sensing. + _cdiDeflection = 30.0 * sawtooth(r / 30.0); + const double VOR_FULL_ARC = 20.0; // VOR is -10 .. 10 degree swing + _cdiDeflection *= VOR_FULL_ARC / _localizerWidth; // increased localiser sensitivity + } else { + // handle the TO side of the VOR + if (fabs(r) > 90.0) { + r = ( r<0.0 ? -r-180.0 : -r+180.0 ); + } + _cdiDeflection = r; + } // of non-localiser case + SG_CLAMP_RANGE(_cdiDeflection, -10.0, 10.0 ); _cdiDeflection *= signal_quality_norm; @@ -514,8 +535,20 @@ void FGNavRadio::updateGlideSlope(double dt, const SGVec3d& aircraft, double sig // needle animation. This means that the needle should peg // when this values is +/-3.5. ////////////////////////////////////////////////////////// - double angle = atan2(heightAboveStationM, dist) * SGD_RADIANS_TO_DEGREES; + double angle = asin( heightAboveStationM / dist ) * SGD_RADIANS_TO_DEGREES; double deflectionAngle = target_gs - angle; + + // The factor of 1.5 gives a period of 6 degrees. + // There will be zeros at 3, 6r, 9, 12r et cetera + // where "r" indicates reverse sensing. + // This is is consistent with conventional pilot lore + // e.g. http://www.allstar.fiu.edu/aerojava/ILS.htm + // but inconsistent with + // http://www.freepatentsonline.com/3757338.html + // + // It may be that some of each exist. + deflectionAngle = 1.5 * sawtooth(deflectionAngle / 1.5); + //SG_CLAMP_RANGE(deflectionAngle, -0.7, 0.7); _gsNeedleDeflection = deflectionAngle * 5.0; _gsNeedleDeflection *= signal_quality_norm; @@ -753,9 +786,10 @@ void FGNavRadio::search() _gs = NULL; } else { // ILS or LOC _gs = globals->get_gslist()->findByFreq(freq, pos); + _localizerWidth = localizerWidth(nav); has_gs_node->setBoolValue(_gs != NULL); twist = 0.0; - effective_range = FG_LOC_DEFAULT_RANGE; + effective_range = nav->get_range(); target_radial = nav->get_multiuse(); SG_NORMALIZE_RANGE(target_radial, 0.0, 360.0); @@ -787,6 +821,36 @@ void FGNavRadio::search() id_c4_node->setIntValue( (int)identBuffer[3] ); } +double FGNavRadio::localizerWidth(FGNavRecord* aLOC) +{ + FGRunway* rwy = aLOC->runway(); + assert(rwy); + + SGVec3d thresholdCart(SGVec3d::fromGeod(rwy->threshold())); + double axisLength = dist(aLOC->cart(), thresholdCart); + double landingLength = dist(thresholdCart, SGVec3d::fromGeod(rwy->end())); + +// Reference: http://dcaa.slv.dk:8000/icaodocs/ +// ICAO standard width at threshold is 210 m = 689 feet = approx 700 feet. +// ICAO 3.1.1 half course = DDM = 0.0775 +// ICAO 3.1.3.7.1 Sensitivity 0.00145 DDM/m at threshold +// implies peg-to-peg of 214 m ... we will stick with 210. +// ICAO 3.1.3.7.1 "Course sector angle shall not exceed 6 degrees." + +// Very short runway: less than 1200 m (4000 ft) landing length: + if (landingLength < 1200.0) { +// ICAO fudges localizer sensitivity for very short runways. +// This produces a non-monotonic sensitivity-versus length relation. + axisLength += 1050.0; + } + +// Example: very short: San Diego KMYF (Montgomery Field) ILS RWY 28R +// Example: short: Tom's River KMJX (Robert J. Miller) ILS RWY 6 +// Example: very long: Denver KDEN (Denver) ILS RWY 16R + double raw_width = 210.0 / axisLength * SGD_RADIANS_TO_DEGREES; + return raw_width < 6.0? raw_width : 6.0; +} + void FGNavRadio::audioNavidChanged() { if ( globals->get_soundmgr()->exists(nav_fx_name)) { diff --git a/src/Instrumentation/navradio.hxx b/src/Instrumentation/navradio.hxx index d61dc88..c7a5980 100644 --- a/src/Instrumentation/navradio.hxx +++ b/src/Instrumentation/navradio.hxx @@ -136,7 +136,8 @@ class FGNavRadio : public SGSubsystem double last_x; double last_loc_dist; double last_xtrack_error; - + double _localizerWidth; // cached localizer width in degrees + string _name; int _num; @@ -170,6 +171,11 @@ class FGNavRadio : public SGSubsystem void clearOutputs(); + /** + * Compute the localizer width in degrees - see implementation for + * more information on the relevant standards and formulae. + */ + double localizerWidth(FGNavRecord* aLOC); FGNavRecord* findPrimaryNavaid(const SGGeod& aPos, double aFreqMHz); public: