From e09ff842187553a4aaeed98da077b27eb0a2dc3b Mon Sep 17 00:00:00 2001
From: priseborough <p_riseborough@live.com.au>
Date: Fri, 24 Oct 2014 20:24:32 +1100
Subject: [PATCH] AP_NavEKF : Don't estimate focal length scale factor without
 reliable velocity

---
 libraries/AP_NavEKF/AP_NavEKF.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libraries/AP_NavEKF/AP_NavEKF.cpp b/libraries/AP_NavEKF/AP_NavEKF.cpp
index 360a66eaf6..2dd88c7be0 100644
--- a/libraries/AP_NavEKF/AP_NavEKF.cpp
+++ b/libraries/AP_NavEKF/AP_NavEKF.cpp
@@ -3689,8 +3689,8 @@ void NavEKF::SetFlightAndFusionModes()
     } else {
         inhibitGndState = false;
     }
-    // Don't update focal length offset state if there is no range finder
-    if (!useRngFinder()) {
+    // Don't update focal length offset state if there is no range finder or GPS, or we are flying slowly
+    if (!useRngFinder() || _fusionModeGPS == 3 || gndSpdSq < 5.0f) {
         fScaleInhibit = true;
     } else {
         fScaleInhibit = false;