Method and apparatus for creating a clothoid road geometry

Patent metadata

Field	Value
Publication number	US-2016245657-A1
Application number	US-201514625722-A
Country	US
Kind code	A1
Filing date	Feb 19, 2015
Priority date	Feb 19, 2015
Publication date	Aug 25, 2016
Grant date	—

Abstract

A method, apparatus and computer program product are provided in order to create a clothoid road geometry. In the context of a method, a link geometry representative of a portion of a road network is converted into a plurality of link splines. The method also includes converting the plurality of link splines into respective sequences of one or more clothoids based upon curvature profiles of the link splines.

First claim

That which is claimed:

1 . A method comprising:
converting a link geometry representative of a portion of a road network into a plurality of link splines; and converting the plurality of link splines into respective sequences of one or more clothoids based upon curvature profiles of the link splines.

2 . A method according to claim 1 wherein converting the plurality of link splines into respective sequences of one or more clothoids comprises, for each link spline:
determining a plurality of break-point locations along a respective link spline dependent upon a curvature profile of the link spline so as to define one or more sections of the link spline based upon the break-point locations; and
converting one or more sections of the respective link spline to respective clothoids.

3 . A method according to claim 2 wherein converting one or more sections of the respective link spline to respective clothoids comprises:
for a section of the respective link spline having a start break-point and an end break-point, determining coordinates of the link spline at the start break-point and the end break-point;
determining tangent headings of the link spline at the start break-point and the end break-point; and
determining the respective clothoid based upon the coordinates and the tangent headings of the link spline at the start break-point and the end break-point.

4 . A method according to claim 2 wherein converting one or more sections of the respective link spline to respective clothoids comprises:
for a section of the respective link spline having a start break-point and an end break-point, determining coordinates of the link spline at the start break-point and the end break-point;
determining curvatures of the link spline at the start break-point and the end break-point; and
determining the respective clothoid based upon the coordinates and the curvatures of the link spline at the start break-point and the end break-point.

5 . A method according to claim 2 further comprising:
determining the curvature profile defining a curvature of the respective link spline at a respective arc length;
identifying one or more zero-crossings in the curvature profile so as to define curves therebetween; and
approximating the curvature profile of a curve with a plurality of polylines, wherein determining the plurality of break-point locations comprises determining the break-point locations based upon vertices and zero-crossings of the plurality of polylines.

6 . A method according to claim 1 wherein converting the link geometry into the plurality of link splines comprises:
defining a plurality of partially overlapping link chains, each link chain comprised of a plurality of links;
converting each link chain into a respective link spline; and
aligning respective ends of the link splines corresponding to overlapping link chains.

7 . A method according to claim 6 further comprising:
subdividing the link geometry comprising a plurality of links into a plurality of tiles; and
aligning respective ends of the link splines that meet at a boundary of a tile.

8 . An apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to, with the processor, cause the apparatus to at least:
convert a link geometry representative of a portion of a road network into a plurality of link splines; and convert the plurality of link splines into respective sequences of one or more clothoids based upon curvature profiles of the link splines.

9 . An apparatus according to claim 8 wherein the at least one memory and computer program code are configured to, with the processor, cause the apparatus to convert the plurality of link splines into respective sequences of one or more clothoids by, for each link spline:
determining a plurality of break-point locations along a respective link spline dependent upon a curvature profile of the link spline so as to define one or more sections of the link spline based upon the break-point locations; and
converting one or more sections of the respective link spline to respective clothoids.

10 . An apparatus according to claim 9 wherein the at least one memory and computer program code are configured to, with the processor, cause the apparatus to convert one or more sections of the respective link spline to respective clothoids by:
for a section of the respective link spline having a start break-point and an end break-point, determining coordinates of the link spline at the start break-point and the end break-point;
determining tangent headings of the link spline at the start break-point and the end break-point; and
determining the respective clothoid based upon the coordinates and the tangent headings of the link spline at the start break-point and the end break-point.

11 . An apparatus according to claim 9 wherein the at least one memory and computer program code are configured to, with the processor, cause the apparatus to convert one or more sections of the respective link spline to respective clothoids by:
for a section of the respective link spline having a start break-point and an end break-point, determining coordinates of the link spline at the start break-point and the end break-point;
determining curvatures of the link spline at the start break-point and the end break-point; and
determining the respective clothoid based upon the coordinates and the curvatures of the link spline at the start break-point and the end break-point.

12 . An apparatus according to claim 9 wherein the at least one memory and computer program code are further configured to, with the processor, cause the apparatus to:
determine the curvature profile defining a curvature of the respective link spline at a respective arc length;
identify one or more zero-crossings in the curvature profile so as to define curves therebetween; and
approximate the curvature profile of a curve with a plurality of polylines, wherein the at least one memory and computer program code are configured to, with the processor, cause the apparatus to determine the plurality of break-point locations by determining the break-point locations based upon vertices and zero-crossings of the plurality of polylines.

13 . An apparatus according to claim 8 wherein the at least one memory and computer program code are configured to, with the processor, cause the apparatus to convert the link geometry into the plurality of link splines by:
defining a plurality of partially overlapping link chains, each link chain comprised of a plurality of links;
converting each link chain into a respective link spline; and
aligning respective ends of the link splines corresponding to overlapping link chains.

14 . An apparatus according to claim 13 wherein the at least one memory and computer program code are further configured to, with the processor, cause the apparatus to:
subdivide the link geometry comprising a plurality of links into a plurality of tiles; and
align respective ends of the link splines that meet at a boundary of a tile.

15 . A computer program product comprising at least one non-transitory computer-readable storage medium having computer-executable program code portions stored therein, the computer-executable program code portions comprising program code instructions configured to:
convert a link geometry representative of a portion of a road network into a plurality of link splines; and convert the plurality of link splines into respective sequences of one or more clothoids based upon curvature pro

Assignees

• Here Global Bv

Inventors

• Dorum Ole Henry

Classifications

• G01C21/32 Primary

  Structuring or formatting of map data · CPC title

• G01C21/3881

  Tile-based structures · CPC title

• G01C21/3819 Primary

  Road shape data, e.g. outline of a route · CPC title