Abstract: A computer implemented method (600) for estimating the position of a movable device in an environment at a required time. First observations are taken (615) by first sensors at various times between the device and plural distributed anchors having known positions in the environment. For each observation taken at a time point within a time window (650), the range and/or angle from the device to the anchor is estimated (640), and the displacement of the device is estimated (660) between the time the observation was taken and the required time is estimated based on second observations taken (625) by second sensors. The position of the anchor is adjusted (665) by the displacement so as to compensate for the effect of the motion of the device. The position of the device (670,680) at the required time is calculated based on the ranges and/or angles and the adjusted anchor positions.