1. A method for generating scaled terrain information with an unmanned autonomous gardening vehicle, the gardening vehicle comprising a driving unit comprising a set of at least one drive wheel, and a motor connected to the at least one drive wheel for providing movability of the gardening vehicle; a gardening-tool; and a camera for capturing images of a terrain, the camera being positioned and aligned in known manner relative to the gardening vehicle; wherein the method comprises: moving the gardening vehicle in the terrain whilst concurrently generating a set of image data by capturing an image series of terrain sections so that at least two images of the image series cover an amount of identical points in the terrain, wherein the terrain sections are defined by a viewing area of the camera at respective positions of the camera while moving; applying a simultaneous localization and mapping (SLAM) algorithm to the set of image data and thereby deriving terrain data, the terrain data comprising: a three-dimensional point cloud representing the captured terrain, and position data relating to a relative position of the gardening vehicle in the terrain; and scaling the three-dimensional point cloud by applying an absolute scale information to the terrain data, wherein the absolute scale information is derived by capturing a reference image of a reference body, of which at least one of the appearance and the position in the terrain is known, and deriving the absolute scale information by image processing based on the appearance of the reference body in the captured reference image and of a known magnification ratio of the camera, wherein at least one of the dimensions, spatial orientation, and shape of the reference body is pre-known.