1. A method for obtaining geometrical information on an object, comprising the steps of: a) moving a camera in a predetermined direction with regard to an object subject to measurement; b) taking a plurality of images of the object by the camera at a plurality of camera positions; c) extracting a plurality of contour images respectively from the plurality of images taken in step b) by the camera, where each of the plurality of contour images contains at least one image element of the object; d) projecting at least one image element in each of the plurality of contour images of the object onto a projected point on a predetermined projection surface, for each of the at least one image element, from a predetermined projection center corresponding to a camera center, to obtain, for each of the at least one image element, a plurality of projected points on a predetermined projection surface as a sequence of movement points (x.sup.t, t=0, 1, 2,. . .) which line up on a first intersection line at which the predetermined projection surface intersects with a first plane containing the predetermined projection center, where the predetermined projection surface is one of a plane and a surface of the second order; e) generating as a sequence of reference points (.tau..sup.t, t=0, 1, 2,. . .), a plurality of points which line up on a second intersection line of the predetermined projection surface and a second plane containing the projection center, so that the sequence of reference points (.tau..sup.t, t=0, 1, 2,. . .) and the sequence of movement points (x.sup.t, t=0, 1, 2,. . .) share a point, and the sequence of reference points (.tau..sup.t, t=0, 1, 2,. . .) is not identical with the sequence of movement points (x.sup.t, t=0, 1, 2,. . .), and has the same cross ratio (inharmonic ratio) as a cross ratio of the sequence of movement points (x.sup.t, t=0, 1, 2,. . .); f) obtaining a first intersection point of a plurality of third intersection lines at which a plurality of third planes respectively intersect the predetermined projection surface, the plurality of third planes each containing the projection center, one movement point in the sequence of movement points (x.sup.t, t=0, 1, 2,. . .), and one reference point, corresponding to the movement point, in the sequence of reference points (.tau..sup.t, t=0, 1, 2,. . .); and g) obtaining geometrical information on the object with respect to the camera position, based on the position of the first intersection point to achieve environment recognition.