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);
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);
- _gsDirect = atan2(dot_v, dot_h) * SGD_RADIANS_TO_DEGREES;
+ 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()) {
}
}
+// 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;
//////////////////////////////////////////////////////////
_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, ' ' );
// GS axis unit tangent vector
// (along the runway):
- _gsAxis = tangentVector(_gs->geod(), _gsCart, gs_radial);
+ _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
projects / flightgear.git / blobdiff