Method and system for determining a position relative to a digital map

A device for determining a longitudinal position of a vehicle relative to a digital map, the digital map comprising data representative of navigable elements of a navigable network along which the vehicle is travelling, the device comprising at least one processor and a memory with computer readable instructions executable by the at least one processor to cause the device to:

• determine real time scan data by scanning a lateral environment around the vehicle using at least one range-finder sensor, said real time scan data comprising one or more depth maps, each depth map representing a measured lateral distance to surfaces in the lateral environment for a plurality of longitudinal positions and elevations;
• retrieve localisation reference data associated with the digital map for a deemed current longitudinal position of the vehicle in relation to the digital map, wherein the localisation reference data comprises one or more depth maps in the form of images, each depth map representing, using corresponding pixel values in the images that comprise a first value indicative of a longitudinal position, a second value indicative of an elevation, and a third value indicative of a lateral position, a lateral distance to surfaces in the lateral environment for a plurality of longitudinal positions and elevations;
• compare the real time scan data to the localisation reference data by calculating a cross-correlation to determine a longitudinal offset between the real time scan data and the localisation reference data;
• and
• adjust the deemed current longitudinal position based on said longitudinal offset to determine the longitudinal position of the vehicle relative to the digital map.