Methods and systems for generating and using localization reference data

1. A method of determining a 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 method comprising:

obtaining localisation reference data associated with the digital map for a deemed current position of the vehicle along a navigable element of the navigable network, wherein the location reference data comprises at least one depth map comprising a plurality of pixels in an image format that are indicative of an environment around the vehicle projected on to a reference plane, the reference plane being defined by a reference line associated with the navigable element, each pixel of the at least one depth map being associated with a position in the reference plane associated with the navigable element along which the vehicle is travelling, and each pixel including a depth channel representing the distance to a surface of an object in the environment along a predetermined direction from the associated position of the pixel in the reference plane and position coordinates indicative of a position in a longitudinal direction along the navigable element and an elevation above ground;

determining real time scan data by scanning the environment around the vehicle using at least one sensor, wherein the real time scan data comprises at least one depth map indicative of an environment around the vehicle, each pixel of the at least one depth map being associated with a position in the reference plane associated with the navigable element, and the pixel including a depth channel representing the distance to a surface of an object in the environment along the predetermined direction from the associated position of the pixel in the reference plane as determined using the at least one sensor and position coordinates indicative of a position in a longitudinal direction along the navigable element and an elevation above ground;

determining a function indicative of a variation in a lateral alignment offset between corresponding pixels of the localisation reference and real time sensor data depth maps with respect to longitudinal position of the pixels along the depth maps; and

using the determined function to adjust the deemed current heading of the vehicle to determine the heading of the vehicle relative to the digital map.

2. The method as claimed in claim 1 , wherein the lateral alignment offset between corresponding pixels is based on the difference in the values indicated by the depth channel data of the pixels.

3. The method as claimed in claim 1 , further comprising shifting the depth maps relative to one another to longitudinally align the depth maps.

4. A non-transitory computer readable medium comprising computer readable instructions executable to cause a system to perform a method as claimed in claim 1 .

5. The method as claimed in claim 1 , wherein the step of determining the function indicative of the variation in lateral alignment offset with longitudinal position comprises determining an average lateral alignment offset of corresponding pixels of the depth maps in each of a plurality of vertical sections through the depth maps along the longitudinal direction of the depth maps.

6. The method as claimed in claim 5 , wherein the function is obtained based upon the variation in the average lateral alignment offset determined for each vertical section along the longitudinal direction of the depth maps.

7. The method as claimed in claim 1 , further comprising determining a longitudinal alignment offset between the depth maps of the localisation reference data and the real time scan data by calculating a correlation between the localisation reference data and the real time scan data.

8. The method as claimed in claim 7 , further comprising using the determined longitudinal alignment offset to adjust the deemed current position to determine the position of the vehicle relative to the digital map.

9. The method as claimed in claim 1 , further comprising determining a lateral alignment offset between the depth maps, wherein the lateral offset is based on a most common lateral offset between corresponding pixels of the depth maps.

10. The method as claimed in claim 9 , further comprising using the determined lateral alignment offset to adjust the deemed current position to determine the position of the vehicle relative to the digital map.

11. The method as claimed in claim 1 , wherein:

(i) a longitudinal alignment offset between the depth maps of the localisation reference data and the real time scan data is determined;

(ii) then the determined longitudinal offset is used to adjust the deemed current position to determine an adjusted current position of the vehicle relative to the digital map;

(iii) then the at least one depth map of the localisation reference data is recomputed based on the adjusted current position;

(iv) then a lateral alignment offset between the recomputed depth map of the localisation reference data and the depth map of the real time scan data is determined;

(v) then the determined longitudinal offset is used to further adjust the adjusted current position to determine a further adjusted current position of the vehicle relative to the digital map;

(vi) then the at least one depth map of the localisation reference data is recomputed based on the further adjusted current position;

(vii) then a function indicative of a variation in a lateral alignment offset between corresponding pixels of the recomputed localisation reference depth map and the real time scan data depth map with respect to longitudinal position of the pixels along the depth maps is determined;

(viii) then the determined function is used to adjust the deemed current heading of the vehicle to determine the heading of the vehicle relative to the digital map; and

(ix) then the at least one depth map of the localisation reference data is recomputed based on the adjusted current heading.

12. The method as claimed in claim 11 , wherein steps (i)-(ix) are repeated until there is substantially zero longitudinal alignment offset and/or substantially zero lateral alignment offset and/or substantially zero heading offset between the recomputed depth map of the localisation reference data and the depth map of the real time scan data.

13. A system for determining a 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 system comprising processing circuitry configured to:

obtain localisation reference data associated with the digital map for a deemed current position of the vehicle along a navigable element of the navigable network, wherein the location reference data comprises at least one depth map comprising a plurality of pixels in an image format that are indicative of an environment around the vehicle projected on to a reference plane, the reference plane being defined by a reference line associated with the navigable element, each pixel of the at least one depth map being associated with a position in the reference plane associated with the navigable element along which the vehicle is travelling, and each pixel including a depth channel representing the distance to a surface of an object in the environment along a predetermined direction from the associated position of the pixel in the reference plane and position coordinates indicative of a position in a longitudinal direction along the navigable element and an elevation above ground;

determine real time scan data by scanning the environment around the vehicle using at least one sensor, wherein the real time scan data comprises at least one depth map indicative of an environment around the vehicle, each pixel of the at least one depth map being associated with a position in the reference plane associated with the navigable element, and the pixel including a depth channel representing the distance to a surface of an object in the environment along the predetermined direction from the associated position of the pixel in the reference plane as determined using the at least one sensor and position coordinates indicative of a position in a longitudinal direction along the navigable element and an elevation above ground;

determine a function indicative of a variation in a lateral alignment offset between corresponding pixels of the localisation reference and real time sensor data depth maps with respect to longitudinal position of the pixels along the depth maps; and

use the determined function to adjust the deemed current heading of the vehicle to determine the heading of the vehicle relative to the digital map.

14. A computer readable storage medium storing instructions that, when executed by one or more processors, cause the one or more processors to perform a method for determining a 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 method comprising:

obtaining localisation reference data associated with the digital map for a deemed current position of the vehicle along a navigable element of the navigable network, wherein the location reference data comprises at least one depth map comprising a plurality of pixels in an image format that are indicative of an environment around the vehicle projected on to a reference plane, the reference plane being defined by a reference line associated with the navigable element, each pixel of the at least one depth map being associated with a position in the reference plane associated with the navigable element along which the vehicle is travelling, and each pixel including a depth channel representing the distance to a surface of an object in the environment along a predetermined direction from the associated position of the pixel in the reference plane and position coordinates indicative of a position in a longitudinal direction along the navigable element and an elevation above ground;

determining real time scan data by scanning the environment around the vehicle using at least one sensor, wherein the real time scan data comprises at least one depth map indicative of an environment around the vehicle, each pixel of the at least one depth map being associated with a position in the reference plane associated with the navigable element, and the pixel including a depth channel representing the distance to a surface of an object in the environment along the predetermined direction from the associated position of the pixel in the reference plane as determined using the at least one sensor and position coordinates indicative of a position in a longitudinal direction along the navigable element and an elevation above ground;

determining a function indicative of a variation in a lateral alignment offset between corresponding pixels of the localisation reference and real time sensor data depth maps with respect to longitudinal position of the pixels along the depth maps; and

using the determined function to adjust the deemed current heading of the vehicle to determine the heading of the vehicle relative to the digital map.