Copter: add Precision Landing to GPS land

ArduCopter/Copter.h

@@ -240,6 +240,7 @@ private:
             enum HomeState home_state   : 2; // 18,19   // home status (unset, set, locked)
             uint8_t using_interlock     : 1; // 20      // aux switch motor interlock function is in use
             uint8_t motor_emergency_stop: 1; // 21      // motor estop switch, shuts off motors when enabled
+            uint8_t land_repo_active    : 1; // 22      // true if the pilot is overriding the landing position
         };
         uint32_t value;
     } ap;

ArduCopter/control_land.cpp

@@ -30,6 +30,9 @@ bool Copter::land_init(bool ignore_checks)
 
     land_pause = false;
 
+    // reset flag indicating if pilot has applied roll or pitch inputs during landing
+    ap.land_repo_active = false;
+
     return true;
 }
 
@@ -91,6 +94,11 @@ void Copter::land_gps_run()
             // process pilot's roll and pitch input
             roll_control = channel_roll->control_in;
             pitch_control = channel_pitch->control_in;
+
+            // record if pilot has overriden roll or pitch
+            if (roll_control != 0 || pitch_control != 0) {
+                ap.land_repo_active = true;
+            }
         }
 
         // get pilot's desired yaw rate
@@ -100,6 +108,13 @@ void Copter::land_gps_run()
     // process roll, pitch inputs
     wp_nav.set_pilot_desired_acceleration(roll_control, pitch_control);
 
+#if PRECISION_LANDING == ENABLED
+    // run precision landing
+    if (!ap.land_repo_active) {
+        wp_nav.shift_loiter_target(precland.get_target_shift(wp_nav.get_loiter_target()));
+    }
+#endif
+
     // run loiter controller
     wp_nav.update_loiter(ekfGndSpdLimit, ekfNavVelGainScaler);