EKF: reset position when stopping GPS use and EV is active

EKF/control.cpp

@@ -616,6 +616,10 @@ void Ekf::controlGpsFusion()
 		// Handle the case where we are using GPS and another source of aiding and GPS is failing checks
 		if (_control_status.flags.gps  && gps_checks_failing && (_control_status.flags.opt_flow || _control_status.flags.ev_pos)) {
 			_control_status.flags.gps = false;
+			// Reset position state to external vision if we are going to use absolute values
+			if (_control_status.flags.ev_pos && !(_params.fusion_mode & MASK_ROTATE_EV)) {
+				resetPosition();
+			}
 			ECL_WARN("EKF GPS data quality poor - stopping use");
 		}