1. A method of determining a 3D trajectory of an object from at least two Observed trajectories of the object in a scene, said observed trajectories being captured in a series of images by at least one camera, each of the images in the series being associated with a pose of the camera, said method comprising the steps of: selecting first and second points of the object from separate parallel planes of the scene; determining, from the series of captured images, a first set of 2D capture locations corresponding to the first point and a second set of 2D capture locations corresponding to the second point; reconstructing, relative to the pose of the camera, the first and second sets of 2D capture locations in the scene to determine a first approximated 3D trajectory from the first set of 2D capture locations in the scene and a second approximated 3D trajectory from the second set of 2D capture locations in the scene; and determining the 3D trajectory of the object based on the first and second approximated 3D trajectories.