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)
+// Calculate a Cartesian unit vector in the
+// local horizontal plane, i.e. tangent to the
+// surface of the earth at the local ground zero.
+// The tangent vector passes through the given <midpoint>
+// and points forward along the given <heading>.
+// The <heading> is given in degrees.
+static SGVec3d tangentVector(const SGGeod& midpoint, 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());
+// The size of the delta is presumably chosen to give
+// numerical stability. I don't know how the value was chosen.
+// It probably doesn't matter much. It gets divided out.
+ double delta(100.0); // in meters
+ SGGeod head, tail;
+ double az2; // ignored
+ SGGeodesy::direct(midpoint, heading, delta, head, az2);
+ SGGeodesy::direct(midpoint, 180+heading, delta, tail, az2);
+ head.setElevationM(midpoint.getElevationM());
+ tail.setElevationM(midpoint.getElevationM());
SGVec3d head_xyz = SGVec3d::fromGeod(head);
- return (head_xyz - tail_xyz) * (1.0/fudge);
+ SGVec3d tail_xyz = SGVec3d::fromGeod(tail);
+// Awkward formula here, needed because vector-by-scalar
+// multiplication is defined, but not vector-by-scalar division.
+ return (head_xyz - tail_xyz) * (0.5/delta);
}
// Create a "serviceable" node with a default value of "true"
-SGPropertyNode_ptr createServiceableProp(SGPropertyNode* aParent, const char* aName)
+SGPropertyNode_ptr createServiceableProp(SGPropertyNode* aParent,
+ const char* aName)
{
- SGPropertyNode_ptr n = (aParent->getChild(aName, 0, true)->getChild("serviceable", 0, true));
+ SGPropertyNode_ptr n =
+ aParent->getChild(aName, 0, true)->getChild("serviceable", 0, true);
simgear::props::Type typ = n->getType();
if ((typ == simgear::props::NONE) || (typ == simgear::props::UNSPECIFIED)) {
n->setBoolValue(true);
gs_deflection_node = node->getChild("gs-needle-deflection", 0, true);
gs_deflection_deg_node = node->getChild("gs-needle-deflection-deg", 0, true);
gs_deflection_norm_node = node->getChild("gs-needle-deflection-norm", 0, true);
+ gs_direct_node = node->getChild("gs-direct-deg", 0, true);
gs_rate_of_climb_node = node->getChild("gs-rate-of-climb", 0, true);
gs_rate_of_climb_fpm_node = node->getChild("gs-rate-of-climb-fpm", 0, true);
gs_dist_node = node->getChild("gs-distance", 0, true);
void FGNavRadio::clearOutputs()
{
inrange_node->setBoolValue( false );
+ signal_quality_norm_node->setDoubleValue( 0.0 );
cdi_deflection_node->setDoubleValue( 0.0 );
cdi_deflection_norm_node->setDoubleValue( 0.0 );
cdi_xtrack_error_node->setDoubleValue( 0.0 );
gs_deflection_node->setDoubleValue( 0.0 );
gs_deflection_deg_node->setDoubleValue(0.0);
gs_deflection_norm_node->setDoubleValue(0.0);
+ gs_direct_node->setDoubleValue(0.0);
gs_inrange_node->setBoolValue( false );
loc_node->setBoolValue( false );
has_gs_node->setBoolValue(false);
bool gsInRange = (gsDist < (_gs->get_range() * SG_NM_TO_METER));
gs_inrange_node->setBoolValue(gsInRange);
- if (!gsInRange) {
- _gsNeedleDeflection = 0.0;
- _gsNeedleDeflectionNorm = 0.0;
- return;
- }
+ if (!gsInRange) return;
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;
+ double comp_h = -dot(pos, _gsAxis); // component in horiz direction
+ double comp_v = dot(pos, _gsVertical); // component in vertical direction
+ //double comp_b = dot(pos, _gsBaseline); // component in baseline direction
+ //if (comp_b) {} // ... (useful for debugging)
+
+// _gsDirect represents the angle of elevation of the aircraft
+// as seen by the GS transmitter.
+ _gsDirect = atan2(comp_v, comp_h) * SGD_RADIANS_TO_DEGREES;
+// At this point, if the aircraft is centered on the glide slope,
+// _gsDirect will be a small positive number, e.g. 3.0 degrees
+
+// Aim the branch cut straight down
+// into the ground below the GS transmitter:
+ if (_gsDirect < -90.0) _gsDirect += 360.0;
+
+ double deflectionAngle = target_gs - _gsDirect;
if (falseCoursesEnabledNode->getBoolValue()) {
// Construct false glideslopes. The scale factor of 1.5
}
}
+// GS is documented to be 1.4 degrees thick,
+// i.e. plus or minus 0.7 degrees from the midline:
+ SG_CLAMP_RANGE(deflectionAngle, -0.7, 0.7);
+
+// Many older instrument xml frontends depend on
+// the un-normalized gs-needle-deflection.
+// Apparently the interface standard is plus or minus 3.5 "volts"
+// for a full-scale deflection:
_gsNeedleDeflection = deflectionAngle * 5.0;
_gsNeedleDeflection *= signal_quality_norm;
- SG_CLAMP_RANGE(deflectionAngle, -0.7, 0.7);
_gsNeedleDeflectionNorm = (deflectionAngle / 0.7) * signal_quality_norm;
//////////////////////////////////////////////////////////
// Calculate desired rate of climb for intercepting the GS
//////////////////////////////////////////////////////////
- double gs_diff = target_gs - angle;
+ double gs_diff = target_gs - _gsDirect;
// convert desired vertical path angle into a climb rate
- double des_angle = angle - 10 * gs_diff;
+ double des_angle = _gsDirect - 10 * gs_diff;
/* printf("target_gs=%.1f angle=%.1f gs_diff=%.1f des_angle=%.1f\n",
- target_gs, angle, gs_diff, des_angle); */
+ target_gs, _gsDirect, gs_diff, des_angle); */
// estimate horizontal speed towards ILS in meters per minute
double elapsedDistance = last_x - gsDist;
//////////////////////////////////////////////////////////
// compute the time to intercept selected radial (based on
- // current and last cross track errors and dt
+ // current and last cross track errors and dt)
//////////////////////////////////////////////////////////
double t = 0.0;
if ( inrange && cdi_serviceable ) {
gs_deflection_node->setDoubleValue(_gsNeedleDeflection);
gs_deflection_deg_node->setDoubleValue(_gsNeedleDeflectionNorm * 0.7);
gs_deflection_norm_node->setDoubleValue(_gsNeedleDeflectionNorm);
+ gs_direct_node->setDoubleValue(_gsDirect);
last_xtrack_error = _cdiCrossTrackErrorM;
}
}
last_time = now;
- play_count = ++play_count % NUM_IDENT_SLOTS;
+ play_count++;
+ play_count %= NUM_IDENT_SLOTS;
// Previous ident is out of time; if still playing, cut it off:
_sgr->stop( nav_fx_name );
_navaid = nav;
string identBuffer(4, ' ');
if (nav) {
- _dme = globals->get_dmelist()->findByFreq(freq, pos);
+ // use ILS signals as DME, otherwise search by frequency
+ if (nav->type()==FGPositioned::ILS)
+ _dme = nav;
+ else
+ _dme = globals->get_dmelist()->findByFreq(freq, pos);
nav_id_node->setStringValue(nav->get_ident());
identBuffer = simgear::strutils::rpad( nav->ident(), 4, ' ' );
if (_gs) {
int tmp = (int)(_gs->get_multiuse() / 1000.0);
target_gs = (double)tmp / 100.0;
-
- // until penaltyForNav goes away, we cannot assume we always pick
- // paired LOC/GS trasmsitters. As we pass over a runway threshold, we
- // often end up picking the 'wrong' LOC, but the correct GS. To avoid
- // breaking the basis computation, ensure we use the GS radial and not
- // the (potentially reversed) LOC radial.
+
double gs_radial = fmod(_gs->get_multiuse(), 1000.0);
SG_NORMALIZE_RANGE(gs_radial, 0.0, 360.0);
-
- // GS axis unit tangent vector
- // (along the runway)
_gsCart = _gs->cart();
- _gsAxis = tangentVector(_gs->geod(), _gsCart, gs_radial);
+
+ // GS axis unit tangent vector
+ // (along the runway):
+ _gsAxis = tangentVector(_gs->geod(), gs_radial);
// GS baseline unit tangent vector
- // (perpendicular to the runay along the ground)
- SGVec3d baseline = tangentVector(_gs->geod(), _gsCart, gs_radial + 90.0);
- _gsVertical = cross(baseline, _gsAxis);
+ // (transverse to the runay along the ground)
+ _gsBaseline = tangentVector(_gs->geod(), gs_radial + 90.0);
+ _gsVertical = cross(_gsBaseline, _gsAxis);
} // of have glideslope
} // of found LOC or ILS