From 1f5c461064ccf009114326848f1a8f5ae259768c Mon Sep 17 00:00:00 2001
From: tsteven4 <tsteven4@gmail.com>
Date: Sun, 18 Dec 2016 16:38:00 -0700
Subject: [PATCH] Fix bug in height filter pointed out by Valerio Messina. 
 height corrections should not be applied if the altitude is unknown.

---
 height.cc | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/height.cc b/height.cc
index f03e6e7ab..963cae681 100644
--- a/height.cc
+++ b/height.cc
@@ -109,12 +109,14 @@ correct_height(const Waypoint* wpt)
 {
   Waypoint* waypointp = (Waypoint*) wpt;
 
-  if (addopt) {
-    waypointp->altitude += addf;
-  }
-
-  if (wgs84tomslopt) {
-    waypointp->altitude -= wgs84_separation(waypointp->latitude, waypointp->longitude);
+  if (waypointp->altitude != unknown_alt) {
+    if (addopt) {
+      waypointp->altitude += addf;
+    }
+  
+    if (wgs84tomslopt) {
+        waypointp->altitude -= wgs84_separation(waypointp->latitude, waypointp->longitude);
+    }
   }
 }
 
-- 
2.30.2