1. A method of determining a terrain parameter relative to a vehicle comprising: registering from the vehicle, when located at a first point in space (O 1 ), a first image including a primary representation (x 11 ,y 11 ) of a first terrain point (P 1 ) and a primary representation (x 21 ,y 21 ) of a second terrain point (P 2 ); registering from the vehicle, when located at a second point in space (O 2 ), a second image (including a secondary representation (x 12 ,y 12 ) of the first terrain point (P 1 ) and a secondary representation (x 22 ,y 22 ) of the second terrain point (P 2 ); calculating the terrain parameter at least based on the first and second images combined with a camera model describing a geometric relationship between a particular terrain point (P) and its projected representation (x,y) onto an image plane; said calculating comprising: determining a first image velocity vector ({overscore (v)} 1 ) which describes a movement of the primary representation (x 11 ,y 11 ) of the first terrain point (P 1 ) in the first image to the secondary representation (x 12 ,y 12 ) thereof in the second image; and determining a second image velocity vector ({overscore (v)} 2 ) which describes a movement of the primary representation (x 21 ,y 21 ) of the second terrain point (P 2 ) in the first image to the secondary representation (x 22 ,y 22 ) thereof in the second image; receiving vehicle movement data describing at least one of a translation between the first and second points in space (O 1 ; O 2 ) and a rotation between the first and second points in space (O 1 ; O 2 ); and resolving a terrain vector ({overscore (Ξ)}) from a respective relationship expressing each of the first and second image velocity vectors ({overscore (v)} 2 , {overscore (v)} 1 ) as a function of at least one of the translation and the rotation, the terrain vector ({overscore (Ξ)}) extending between one of the first and second points in space (O 1 ; O 2 ) and a particular terrain point (T) in proximity of the vehicle.