Navigation for a robotic work tool

A method for operating a robotic work tool, said robotic work tool comprising a position determining device configured to determine a current position of the robotic work tool and at least one deduced reckoning navigation sensor configured to provide signals for deduced reckoning navigation, the method comprising:

• in response to the position determining device no longer being able to determine the current position, operating the robotic work tool based on the deduced reckoning navigation via the at least one deduced reckoning navigation sensor;
• subsequently determining that the position determining device is able to determine the current position of the robotic work tool, and in response thereto, determining an expected navigation parameter based on control data for the deduced reckoning navigation sensor, the expected navigation parameter comprising an expected position and an expected direction of travel of the robotic work tool;
• comparing the expected navigation parameter to a current navigation parameter to determine a navigation error, the current navigation parameter comprising the current position as indicated by the position determining device and a current direction of travel of the robotic work tool as determined from the position determining tool;
• determining if the navigation error exceeds a navigation error threshold;
• in response to the navigation error exceeding the navigation error threshold, causing the robotic work tool to change a trajectory to accommodate for the navigation error by aligning the trajectory with an expected trajectory of the robotic work tool, wherein the expected trajectory is determined as being along the expected direction originating from the expected position of the robotic work tool;
• and
• performing the change of the trajectory by returning to a position and aligning the trajectory while at that position with the expected direction originating from the expected position of the robotic work tool, the position not coinciding with the expected position;
• wherein the position is determined to be a point in an area in which navigation via the position determining device is not possible, or the position is a point along the expected trajectory.