From 6fbed62f6f5a545121bb8373b4021b89d8f32356 Mon Sep 17 00:00:00 2001
From: marko <marko.kl.berkenbusch@gmail.com>
Date: Tue, 25 Aug 2020 10:37:08 -0400
Subject: [PATCH] Fix great circle formula in gpsnav

---
 apps/gpsnav/app.js | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/apps/gpsnav/app.js b/apps/gpsnav/app.js
index 1e70b0cd3..3bbc756b7 100644
--- a/apps/gpsnav/app.js
+++ b/apps/gpsnav/app.js
@@ -93,9 +93,8 @@ function bearing(a,b){
 }
 
 function distance(a,b){
-  var x = radians(a.lon-b.lon) * Math.cos(radians((a.lat+b.lat)/2));
-  var y = radians(b.lat-a.lat);
-  return Math.round(Math.sqrt(x*x + y*y) * 6371000);
+  var dsigma = Math.acos(Math.sin(radians(a.lat))*Math.sin(radians(b.lat))+Math.cos(radians(a.lat))*Math.cos(radians(b.lat))*Math.cos(radians(a.lon-b.lon)));
+  return Math.round(dsigma*6371000);
 }
 
 var selected = false;