1. A method of providing a descriptor for at least one feature of an image, comprising the steps of: providing an image captured by a capturing device and extracting at least one feature from the image; and assigning a descriptor to the at least one feature, the descriptor depending on at least one parameter which is indicative of an orientation in the image with respect to a projection of the direction of the gravitational force in the image, wherein the at least one parameter is determined from at least one tracking system; and wherein the at least one parameter is determined under consideration of intrinsic parameters of the capturing device.