Use the Vincenty formula rather than the Haversine formula for earth_distance.

Vincenty is much better behaved with small distances. This is a translation of
http://www.movable-type.co.uk/scripts/latlong-vincenty.html

While I'm here, put a couple of WGS84 constants into a header.

1 files changed, 3 insertions, 0 deletions

diff --git a/gps.h b/gps.h
index 7a06c15b..5ad4b5be 100644
--- a/gps.h
+++ b/gps.h
@@ -35,6 +35,9 @@ extern "C" {
 #define MAXCHANNELS	20	/* maximum GPS channels (*not* satellites!) */
 #define GPS_PRNMAX	32	/* above this number are SBAS satellites */
 
+#define WGS84A 6378137		/* equatorial radius */
+#define WGS84F 298.257223563	/* flattening */
+#define WGS84B 6356752.3142	/* polar radius */
 /* 
  * The structure describing an uncertainty volume in kinematic space.
  * This is what GPSes are meant to produce; all the other info is