From 44302bb1998ab75162de11387bc9ad3435ee3f83 Mon Sep 17 00:00:00 2001
From: Oliver Jowett <oliver@mutability.co.uk>
Date: Wed, 18 Feb 2015 01:53:47 +0000
Subject: [PATCH] Fix NaN in greatcircle calc if positions are identical.

Bail out early if there's a global CPR decoding error so we don't try
to do range/speed checks on a position of (0,0)
---
 track.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/track.c b/track.c
index f1e1c07..1977ab8 100644
--- a/track.c
+++ b/track.c
@@ -120,6 +120,11 @@ static double greatcircle(double lat0, double lon0, double lat1, double lon1)
     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;
+
     return 6371e3 * acos(sin(lat0) * sin(lat1) + cos(lat0) * cos(lat1) * cos(fabs(lon0 - lon1)));
 }
 
@@ -131,6 +136,7 @@ static int speed_check(struct aircraft *a, double lat, double lon, uint64_t now,
     double distance;
     double range;
     int speed;
+    int inrange;
 
     if (!(a->bFlags & MODES_ACFLAGS_LATLON_VALID))
         return 1; // no reference, assume OK
@@ -164,14 +170,15 @@ static int speed_check(struct aircraft *a, double lat, double lon, uint64_t now,
     // find actual distance
     distance = greatcircle(a->lat, a->lon, lat, lon);
 
+    inrange = (distance <= range);
 #ifdef DEBUG_CPR_CHECKS
-    if (distance >= range) {
+    if (!inrange) {
         fprintf(stderr, "Speed check failed: %06x: %.3f,%.3f -> %.3f,%.3f in %.1f seconds, max speed %d kt, range %.1fkm, actual %.1fkm\n",
                 a->addr, a->lat, a->lon, lat, lon, elapsed/1000.0, speed, range/1000.0, distance/1000.0);
     }
 #endif
 
-    return (distance < range);
+    return inrange;
 }
 
 static int doGlobalCPR(struct aircraft *a, int fflag, int surface, uint64_t now, double *lat, double *lon, unsigned *nuc)
@@ -211,6 +218,9 @@ static int doGlobalCPR(struct aircraft *a, int fflag, int surface, uint64_t now,
                                    lat, lon);
     }
 
+    if (result < 0)
+        return result;
+
     // check max range
     if (Modes.maxRange > 0 && (Modes.bUserFlags & MODES_USER_LATLON_VALID)) {
         double range = greatcircle(Modes.fUserLat, Modes.fUserLon, *lat, *lon);