However, we can create a 2D noise function that approximates the appearance of a true 3D noise function, using spot noise . We take into account the object space coordinates of the geometry, and generate only spots that are close enough to the geometry to make a contribution to the 3D noise at those points. The difficulty is how to render the spot in such a way that at each fragment the value of the spot is determined by the object space distance from the center of the spot to that fragment. Depending on the complexity of the geometry, we may be able to make an acceptable approximation to the correct spot value by distorting the spot texture. One possible way to improve the approximation is to compensate for a nonuniform mapping of the noise texture to the geometry. Van Wijk describes how he does this by nonuniformly scaling a spot. Approximating the correct spot value is most important when generating the lower octaves, where the spots are largest and errors are most noticeable.