From 5bda871d603ec379dde84c89084093cf002012c5 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <tridge@samba.org>
Date: Fri, 23 Dec 2011 08:28:56 +1100
Subject: [PATCH] added comment on using GPS ground course

---
 ArduPlane/navigation.pde | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/ArduPlane/navigation.pde b/ArduPlane/navigation.pde
index 776886da01..4aa68f3ad9 100644
--- a/ArduPlane/navigation.pde
+++ b/ArduPlane/navigation.pde
@@ -106,6 +106,15 @@ static void calc_gndspeed_undershoot()
 static void calc_bearing_error()
 {
 	if(takeoff_complete == true  || g.compass_enabled == true) {
+        /*
+          most of the time we use the yaw sensor for heading, even if
+          we don't have a compass. The yaw sensor is drift corrected
+          in the DCM library. We only use the gps ground course
+          directly if we haven't completed takeoff, as the yaw drift
+          correction won't have had a chance to kick in. Drift
+          correction using the GPS typically takes 10 seconds or so
+          for a 180 degree correction.
+         */
 		bearing_error = nav_bearing - dcm.yaw_sensor;
 	} else {