Method to determine the orientation of a target vehicle

1. A method to determine the heading or orientation of a target vehicle by a host vehicle, said host vehicle equipped with a lidar or radar system, said system including a sensor unit adapted to receive signals emitted from said host vehicle and reflected by said target vehicle, comprising:

a) determining at least one reference angle being an initial estimate of target heading or orientation (β);

b) emitting a signal from said system and determining a plurality of point radar or lidar detections belonging to said a target vehicle, said point detections having co-ordinates in the horizontal plane;

c) formulating an initial rectangular boundary box from said point detections, where the bounding box is formulated such that such that two edges of the boundary box are drawn parallel to the reference angle and two sides are perpendicular to the reference angle and such that all the detections are either on the bounding box sides or lay within the bounding box and each edge has at least one detection point on it;

d) for each point on lying on an edge of the boundary box, rotating a line coincident with the respective edge clockwise and anticlockwise until said line intersects another point detection or until a maximum angle of rotation is performed; and each time when said line intersects said another point detection, determining a correction angle Δi, where the correction angle is such that applied to the reference angle it gives an orientation candidate angle γi;

e) in respect of each orientation candidate angle γi/correction angle Δi, determining a cost function;

f) selecting that orientation candidate angle having the lowest cost function.

2. The method as claimed in claim 1 , wherein step d) is only performed in respect of detection points lying on visible edges.

3. The method as claimed in claim 1 , wherein if two values of correction angle (Δi) are found in respect of respective clockwise and anticlockwise rotation with respect to a detection point, only formulating an orientation candidate from the smallest of the two correction angles (Δi).

4. The method as claimed in claim 1 , wherein step f) comprises selecting the orientation candidate with the smallest value of the correction angle Δi.

5. The method as claimed in claim 1 , wherein step d) determining the distance between the said point on lying on an edge of the initial boundary box, and the point detection intersect by said line, and wherein said step f) selects the orientation candidate angle formulated for the instance where said distance is largest.

6. The method as claimed in claim 1 , wherein for each case in step d) when said line intersects said another point detection, formulating a revised boundary box, where one edge of said boundary box is formed coincident with a line from said point lying on said edge of the initial boundary box and said point detection intersect by the said line which is rotated, and where another edge is parallel with said edge of said revised boundary box and the other two edges are perpendicular thereto and such and each edge has at least one detection point on it.

7. The method of claim 6 wherein said cost function is the area of said revised boundary box.

8. The method of claim 6 , wherein said cost function is the sum the shortest distance between each point detection not lying on the revised boundary box and its nearest edge.