# include <config.h>
#endif
+#include "navradio.hxx"
+
#include <sstream>
#include <simgear/sg_inlines.h>
#include <simgear/structure/exception.hxx>
#include <simgear/math/interpolater.hxx>
-#include "Navaids/navrecord.hxx"
+#include <Navaids/navrecord.hxx>
+
+#include <Airports/runways.hxx>
#include <Navaids/navlist.hxx>
#include <Main/util.hxx>
-#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;
+}
+
+// Calculate a unit vector in the horizontal tangent plane
+// starting at the given "tail" of the vector and going off
+// with the given heading.
+static SGVec3d tangentVector(const SGGeod& tail, const SGVec3d& tail_xyz,
+ const double heading)
+{
+// The fudge factor here is presumably intended to improve
+// numerical stability. I don't know if it is necessary.
+// It gets divided out later.
+ double fudge(100.0);
+ SGGeod head;
+ double az2; // ignored
+ SGGeodesy::direct(tail, heading, fudge, head, az2);
+ head.setElevationM(tail.getElevationM());
+ SGVec3d head_xyz = SGVec3d::fromGeod(head);
+ return (head_xyz - tail_xyz) * (1.0/fudge);
+}
+
// Constructor
FGNavRadio::FGNavRadio(SGPropertyNode *node) :
lon_node(fgGetNode("/position/longitude-deg", true)),
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)
}
// 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;
void FGNavRadio::updateGlideSlope(double dt, const SGVec3d& aircraft, double signal_quality_norm)
{
+ _gsNeedleDeflection = 0.0;
if (!_gs || !inrange_node->getBoolValue()) {
gs_dist_node->setDoubleValue( 0.0 );
return;
}
- // find closest distance to the gs base line
- double dist = sgdClosestPointToLineDistSquared(aircraft.data(), _gs->cart().data(),
- gs_base_vec.data());
- dist = sqrt(dist);
- gs_dist_node->setDoubleValue(dist);
- double heightAboveStationM =
- (alt_node->getDoubleValue() - _gs->elevation()) * SG_FEET_TO_METER;
+ double gsDist = dist(aircraft, _gsCart);
+ gs_dist_node->setDoubleValue(gsDist);
+ if (gsDist > (_gs->get_range() * SG_NM_TO_METER)) {
+ return;
+ }
- //////////////////////////////////////////////////////////
- // compute the amount of glide slope needle deflection
- // (.i.e. the number of degrees we are off the glide slope * 5.0
- //
- // CLO - 13 Mar 2006: The glide slope needle should peg at
- // +/-0.7 degrees off the ideal glideslope. I'm not sure why
- // we compute the factor the way we do (5*gs_error), but we
- // need to compensate for our 'odd' number in the glideslope
- // needle animation. This means that the needle should peg
- // when this values is +/-3.5.
- //////////////////////////////////////////////////////////
- double angle = atan2(heightAboveStationM, dist) * SGD_RADIANS_TO_DEGREES;
+ SGVec3d pos = aircraft - _gsCart; // relative vector from gs antenna to aircraft
+ // The positive GS axis points along the runway in the landing direction,
+ // toward the far end, not toward the approach area, so we need a - sign here:
+ double dot_h = -dot(pos, _gsAxis);
+ double dot_v = dot(pos, _gsVertical);
+ double angle = atan2(dot_v, dot_h) * SGD_RADIANS_TO_DEGREES;
double deflectionAngle = target_gs - angle;
- //SG_CLAMP_RANGE(deflectionAngle, -0.7, 0.7);
+
+ // Construct false glideslopes. The scale factor of 1.5
+ // in the sawtooth 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.
+ if (deflectionAngle < 0) {
+ deflectionAngle = 1.5 * sawtooth(deflectionAngle / 1.5);
+ } else {
+ // no false GS below the true GS
+ }
+
_gsNeedleDeflection = deflectionAngle * 5.0;
_gsNeedleDeflection *= signal_quality_norm;
+
+ SG_CLAMP_RANGE(deflectionAngle, -0.7, 0.7);
_gsNeedleDeflectionNorm = (deflectionAngle / 0.7) * signal_quality_norm;
- SG_CLAMP_RANGE(_gsNeedleDeflectionNorm, -1.0, 1.0);
//////////////////////////////////////////////////////////
// Calculate desired rate of climb for intercepting the GS
double des_angle = angle - 10 * gs_diff;
// estimate horizontal speed towards ILS in meters per minute
- double elapsedDistance = last_x - dist;
- last_x = dist;
+ double elapsedDistance = last_x - gsDist;
+ last_x = gsDist;
double new_vel = ( elapsedDistance / dt );
horiz_vel = 0.75 * horiz_vel + 0.25 * new_vel;
_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);
int tmp = (int)(_gs->get_multiuse() / 1000.0);
target_gs = (double)tmp / 100.0;
- SGGeod baseLine;
- double dummy;
- SGGeodesy::direct(_gs->geod(), target_radial + 90.0, 100.0, baseLine, dummy);
- gs_base_vec = SGVec3d::fromGeod(baseLine) - _gs->cart();
+ // GS axis unit tangent vector
+ // (along the runway)
+ _gsCart = _gs->cart();
+ _gsAxis = tangentVector(_gs->geod(), _gsCart, target_radial);
+
+ // GS baseline unit tangent vector
+ // (perpendicular to the runay along the ground)
+ SGVec3d baseline = tangentVector(_gs->geod(), _gsCart, target_radial + 90.0);
+ _gsVertical = cross(baseline, _gsAxis);
} // of have glideslope
} // of found LOC or ILS
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)) {
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