Copter: clean up land detector and modify to use desired velocity

ArduCopter/control_land.pde

@@ -208,14 +208,13 @@ static bool land_complete_maybe()
 // called at 50hz
 static void update_land_detector()
 {
-    // detect whether we have landed by watching for low climb rate, motors hitting their lower limit, overall low throttle and low rotation rate
-    if ((abs(climb_rate) < LAND_DETECTOR_CLIMBRATE_MAX) &&
-        (abs(baro_climbrate) < LAND_DETECTOR_BARO_CLIMBRATE_MAX) &&
-        motors.limit.throttle_lower &&
-#if FRAME_CONFIG != HELI_FRAME
-        (motors.get_throttle_out() < get_non_takeoff_throttle()) &&
-#endif
-        (ahrs.get_gyro().length() < LAND_DETECTOR_ROTATION_MAX)) {
+    bool climb_rate_small = abs(climb_rate) < LAND_DETECTOR_CLIMBRATE_MAX;
+    bool target_climb_rate_low = !pos_control.is_active_z() || pos_control.get_desired_velocity().z < LAND_SPEED;
+    bool motor_at_lower_limit = motors.limit.throttle_lower;
+    bool throttle_low = FRAME_CONFIG == HELI_FRAME || motors.get_throttle_out() < get_non_takeoff_throttle();
+    bool not_rotating_fast = ahrs.get_gyro().length() < LAND_DETECTOR_ROTATION_MAX;
+    
+    if (climb_rate_small && target_climb_rate_low && motor_at_lower_limit && throttle_low && not_rotating_fast) {
         if (!ap.land_complete) {
             // increase counter until we hit the trigger then set land complete flag
             if( land_detector < LAND_DETECTOR_TRIGGER) {