The optical texture of the light reflected from the physical texture of the paper and projected to the station point of the rat was, therefore, about 15 times smaller and denser on one side than on the other. The compactness of an optical texture in itself is ambiguous, since it may correspond to a near surface of fine structure or a far surface of coarse structure. A transformation of the pattern of an optic array, both the whole and all its parts, corresponds to a change of the station-point, that is, to a change in the animal’s point of view. The shape of a closed contour without motion or texture does not specify the shape of an object in the environment. A great many properties of a tridimensional environment are unaltered in a bidimensional projection to a point. They are, as the geometer says, invariant under projection.