Abstract: The object of the invention is a method and apparatus for measuring the characteristic quantities, such as e.g., the length, diameter, volume, and defects of a log (1) or similar in which method the log (1) is moved at a known speed past a photographing station. The photographing station consists of at least one plane of light (4.1) that transects the direction of travel of the log and a video camera (3) set at a fixed angle (a) to this, and a computer apparatus (6), which is arranged to calculate and collect sequential images of a group of surface points (x.sub.l, y.sub.l, z.sub.l ; . . . ; x.sub.n, y.sub.n, z.sub.n) of a three-dimensional model depicting the surface of the log as the log moves through the plane of light, in which the coordinates of each point are calculated with the aid of the geometry of the photography. The log (1) is transported transversely to the direction of the conveyor, the log then traveling along an imagined plane, while the plane of light (4.