AP_Baro: added update_calibration() method

used for auto baro calibration when disarmed

libraries/AP_Baro/AP_Baro.cpp

@@ -118,6 +118,17 @@ void AP_Baro::calibrate()
     _ground_temperature.set_and_save(ground_temperature);
 }
 
+/**
+   update the barometer calibration
+   this updates the baro ground calibration to the current values. It
+   can be used before arming to keep the baro well calibrated
+*/
+void AP_Baro::update_calibration()
+{
+    _ground_pressure.set(get_pressure());
+    _ground_temperature.set(get_temperature());
+}
+
 // return current altitude estimate relative to time that calibrate()
 // was called. Returns altitude in meters
 // note that this relies on read() being called regularly to get new data

libraries/AP_Baro/AP_Baro.h

@@ -33,6 +33,10 @@ public:
     // the callback is a delay() like routine
     void        calibrate();
 
+    // update the barometer calibration to the current pressure. Can
+    // be used for incremental preflight update of baro
+    void        update_calibration();
+
     // get current altitude in meters relative to altitude at the time
     // of the last calibrate() call
     float        get_altitude(void);