Methods and apparatus for processing of GNSS signals are presented. These include GNSS processing with obtaining GNSS data derived from signals received at a rover antenna, obtaining correction data, maintaining a time sequence of at least one rover position and at least one rover position difference with associated time tags, using the time sequence to determine at least one derived rover position by, starting from a position determined using corrections synchronous with rover data as an anchor position at a time tag, deriving a new anchor position for the time tag of the anchor position and at least one other estimated rover position at the time tag of the anchor position, and/or reporting the new anchor position and/or a new derived rover position.