Here is a little patch that changes the behaviour of the VOR CDI and OFF-flag
for indicators like the HSI when getting outside the range of the VOR
station.
Currently, when flying at a distance between the effective_range and twice the
effective_range of a VOR station, the in-range property is computed based on
a random value, causing the OFF Flag and the CDI bar to perform an ugly
jitter.
The attached patch introduces a new property signal-quality-norm which is
computed based on the distance to the station and the range. It is 1.0 when
the distance is less than the range and decreases by 1/x^2 for distances
greater than the range leading to a signal-quality-norm of 0.25 for distances
two times the range, 0.125 for three times the range and so on.
The in-range flag is tied to a signal-quality-norm greater than 0.2 (fixed
squelch).
The CDI and GS needle deflection is multiplied with the signal-quality-norm.
The benefit is:
- Ability to animate the OFF-Flag with a smooth transition.
- CDI and GS needle deflection shows correct values when in range
(signal-quality-norm=1.0) and show some wrong indication when the range is
exceeded
- CDI and GS needle start to move, even when the OFF flag is visible
- No more jitter for flag and needles
See the new SenecaII ki525a hsi as an example at
http://www.t3r.de/fg/navpatch.jpg
The numbers on the image are:
(1) the new property signal-quality-norm
(2) distance exceeds the effective-range by 30%
(3) NAV flag has a rotation animation bound to signal-quality-norm and is
partially visible
(4) CDI is partially deflected even with NAV flag shown
This implementation better matches reality - at least, how I observed it ;-)
The attached patch is agains current HEAD.
I hope the patch gets into CVS with the help of some kind commiter.
Greetings, Torsten
Index: navradio.cxx
===================================================================
RCS file: /var/cvs/FlightGear-0.9/source/src/Instrumentation/navradio.cxx,v
retrieving revision 1.29
diff -u -p -r1.29 navradio.cxx
--- navradio.cxx 3 Aug 2008 14:34:42 -0000 1.29
+++ navradio.cxx 28 Aug 2008 18:28:08 -0000
@@ -35,6 +35,7 @@
#include <simgear/structure/exception.hxx>
#include <Navaids/navlist.hxx>
+#include <Main/util.hxx>
#include "navradio.hxx"
using std::string;
@@ -68,6 +69,7 @@ FGNavRadio::FGNavRadio(SGPropertyNode *n
to_flag_node(NULL),
from_flag_node(NULL),
inrange_node(NULL),
+ signal_quality_norm_node(NULL),
cdi_deflection_node(NULL),
cdi_xtrack_error_node(NULL),
cdi_xtrack_hdg_err_node(NULL),
@@ -176,6 +178,7 @@ FGNavRadio::init ()
to_flag_node = node->getChild("to-flag", 0, true);
from_flag_node = node->getChild("from-flag", 0, true);
inrange_node = node->getChild("in-range", 0, true);
+ signal_quality_norm_node = node->getChild("signal-quality-norm", 0, true);
cdi_deflection_node = node->getChild("heading-needle-deflection", 0, true);
cdi_xtrack_error_node = node->getChild("crosstrack-error-m", 0, true);
cdi_xtrack_hdg_err_node
@@ -314,6 +317,8 @@ FGNavRadio::update(double dt)
bool has_gs = has_gs_node->getBoolValue();
bool is_loc = loc_node->getBoolValue();
double loc_dist = loc_dist_node->getDoubleValue();
+ double effective_range_m;
+ double signal_quality_norm = signal_quality_norm_node->getDoubleValue();
double az1, az2, s;
@@ -418,18 +423,32 @@ FGNavRadio::update(double dt)
effective_range
= adjustNavRange( nav_elev, pos.getElevationM(), range );
}
+
+ effective_range_m = effective_range * SG_NM_TO_METER;
+
// cout << "nav range = " << effective_range
// << " (" << range << ")" << endl;
- if ( loc_dist < effective_range * SG_NM_TO_METER ) {
- inrange = true;
- } else if ( loc_dist < 2 * effective_range * SG_NM_TO_METER ) {
- inrange = sg_random() < ( 2 * effective_range * SG_NM_TO_METER
- - loc_dist )
- / (effective_range * SG_NM_TO_METER);
- } else {
- inrange = false;
- }
+ //////////////////////////////////////////////////////////
+ // compute signal quality
+ // 100% within effective_range
+ // decreases 1/x^2 further out
+ //////////////////////////////////////////////////////////
+ {
+ double last_signal_quality_norm = signal_quality_norm;
+
+ if ( loc_dist < effective_range_m ) {
+ signal_quality_norm = 1.0;
+ } else {
+ double range_exceed_norm = loc_dist/effective_range_m;
+ signal_quality_norm = 1/(range_exceed_norm*range_exceed_norm);
+ }
+
+ signal_quality_norm = fgGetLowPass( last_signal_quality_norm,
+ signal_quality_norm, dt );
+ }
+ signal_quality_norm_node->setDoubleValue( signal_quality_norm );
+ inrange = signal_quality_norm > 0.2;
inrange_node->setBoolValue( inrange );
if ( !is_loc ) {
@@ -507,6 +526,7 @@ FGNavRadio::update(double dt)
r *= 4.0;
}
SG_CLAMP_RANGE( r, -10.0, 10.0 );
+ r *= signal_quality_norm;
}
}
cdi_deflection_node->setDoubleValue( r );
@@ -591,6 +611,7 @@ FGNavRadio::update(double dt)
// cout << "dist = " << x << " height = " << y << endl;
double angle = asin( y / x ) * SGD_RADIANS_TO_DEGREES;
r = (target_gs - angle) * 5.0;
+ r *= signal_quality_norm;
}
}
gs_deflection_node->setDoubleValue( r );
Index: navradio.hxx
===================================================================
RCS file: /var/cvs/FlightGear-0.9/source/src/Instrumentation/navradio.hxx,v
retrieving revision 1.16
diff -u -p -r1.16 navradio.hxx
--- navradio.hxx 6 Dec 2006 22:13:01 -0000 1.16
+++ navradio.hxx 28 Aug 2008 18:28:08 -0000
@@ -18,7 +18,7 @@
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
//
-// $Id: navradio.hxx,v 1.16 2006/12/06 22:13:01 mfranz Exp $
+// $Id: navradio.hxx,v 1.16 2006-12-06 22:13:01 mfranz Exp $
#ifndef _FG_NAVRADIO_HXX
@@ -85,6 +85,7 @@ class FGNavRadio : public SGSubsystem
SGPropertyNode_ptr to_flag_node;
SGPropertyNode_ptr from_flag_node;
SGPropertyNode_ptr inrange_node;
+ SGPropertyNode_ptr signal_quality_norm_node;
SGPropertyNode_ptr cdi_deflection_node;
SGPropertyNode_ptr cdi_xtrack_error_node;
SGPropertyNode_ptr cdi_xtrack_hdg_err_node;
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