A robotic work tool system (200) comprising a charging station (210) and a robotic work tool (100), said robotic work tool (100) comprising a position determining device (190) for determining a current position, the robotic work tool (100) being configured to determine that reliable navigation through said position determining device (190) is no longer possible, such as when satellite signal reception is not possible, at a time point (T1) and position and in response thereto generate an obstacle map which gives information on the position of at least one obstacle (260), determine when an area will be shadowed with regards to satellite reception based on said obstacle map, and to schedule operation of the robotic work tool (100) accordingly.
