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Various LOC/GS improvements from John Denker, adapted to trunk by me (hopefully not introducing too many bugs along the way). Includes:

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- false LOC courses and GS lobes
 - LOC sensitivity based on runway dimensions
 - GS cutoff based on range
 - More accurate GS deviation computation, making final approach more stable
This commit is contained in:
jmt 2009-09-11 23:05:23 +00:00 committed by Tim Moore
parent 606f9173b2
commit 3c48943e81
2 changed files with 136 additions and 44 deletions
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167
src/Instrumentation/navradio.cxx
View file

@ -25,6 +25,8 @@
# include <config.h>
#endif
#include "navradio.hxx"
#include <sstream>
#include <simgear/sg_inlines.h>
@ -36,13 +38,46 @@
#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)),
@ -102,6 +137,7 @@ 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 +498,24 @@ 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 ) {
if ( is_loc ) {
// 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 );
}
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;
}
} // of non-localiser case
SG_CLAMP_RANGE(_cdiDeflection, -10.0, 10.0 );
_cdiDeflection *= signal_quality_norm;
@ -490,37 +529,47 @@ void FGNavRadio::updateReceiver(double dt)
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
@ -530,8 +579,8 @@ void FGNavRadio::updateGlideSlope(double dt, const SGVec3d& aircraft, double sig
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;
@ -753,9 +802,10 @@ 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);
@ -764,10 +814,15 @@ void FGNavRadio::search()
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
@ -787,6 +842,36 @@ 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)) {

9
src/Instrumentation/navradio.hxx
View file

@ -126,7 +126,6 @@ class FGNavRadio : public SGSubsystem
bool has_dme;
double target_radial;
SGVec3d gs_base_vec;
SGTimeStamp prev_time;
SGTimeStamp curr_time;
double effective_range;
@ -136,6 +135,7 @@ 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;
@ -143,6 +143,8 @@ class FGNavRadio : public SGSubsystem
// internal periodic station search timer
double _time_before_search_sec;
SGVec3d _gsCart, _gsAxis, _gsVertical;
// CDI properties
bool _toFlag, _fromFlag;
double _cdiDeflection;
@ -170,6 +172,11 @@ 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: