We have just seen that, in going from Euclidean to projective, a point in becomes a set of points in which are related to each other by means of a nonzero scaling factor. Therefore, a point in can be visualized as a ``line'' 2 in three-dimensional space passing through the origin and the point (Technically speaking, the line does not include the origin). This three-dimensional space is known as the ray space (among other names) and is shown in Figure 3. Similarly, a line in can be visualized as a ``plane'' passing through the origin and perpendicular to . The ideal line is the horizontal W=0 ``plane'', and the ideal points are ``lines'' in this ``plane.''