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Use the haversine formula for small greatcircle distances, rather

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than clamping to zero.
This commit is contained in:
Oliver Jowett 2016-08-26 11:36:29 +01:00
parent a910454c02
commit 08c14484cd
1 changed files with 12 additions and 4 deletions
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16
track.c
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@ -112,16 +112,24 @@ struct aircraft *trackFindAircraft(uint32_t addr) {
// (but we don't use it in situations where that matters)
static double greatcircle(double lat0, double lon0, double lat1, double lon1)
{
double dlat, dlon;
lat0 = lat0 * M_PI / 180.0;
lon0 = lon0 * M_PI / 180.0;
lat1 = lat1 * M_PI / 180.0;
lon1 = lon1 * M_PI / 180.0;
// avoid NaN
if (fabs(lat0 - lat1) < 0.0001 && fabs(lon0 - lon1) < 0.0001)
return 0.0;
dlat = fabs(lat1 - lat0);
dlon = fabs(lon1 - lon0);
return 6371e3 * acos(sin(lat0) * sin(lat1) + cos(lat0) * cos(lat1) * cos(fabs(lon0 - lon1)));
// use haversine for small distances for better numerical stability
if (dlat < 0.001 && dlon < 0.001) {
double a = sin(dlat/2) * sin(dlat/2) + cos(lat0) * cos(lat1) * sin(dlon/2) * sin(dlon/2);
return 6371e3 * 2 * atan2(sqrt(a), sqrt(1.0 - a));
}
// spherical law of cosines
return 6371e3 * acos(sin(lat0) * sin(lat1) + cos(lat0) * cos(lat1) * cos(dlon));
}
static void update_range_histogram(double lat, double lon)