Vanishing point to the axis which is cut by this image plane will have images that meet at a single vanishing point. Lines parallel to the other two axes will not form vanishing points as they are parallel to the image plane. This is one-point perspective. Similarly, when the image plane intersects two world-coordinate axes, lines parallel to those planes will meet form two vanishing points in the picture plane. This is called two-point perspective. In three-point perspective the image plane intersects the , , and axes and therefore lines parallel to these axes intersect, resulting in three different vanishing points. The
Tricritical point more components. It can be shown that three is the "minimum" number of components for which these points can appear. In this case, one may have a two-dimensional region of three-phase coexistence ("F" = 2-3+3 =2) (thus, each point in this region corresponds to a triple point). This region (F=2, P=3) will terminate in two critical lines of two-phase coexistence; these two critical lines (F=1, P=2) may then terminate at a single tricritical point. This point (F=0, P=1) is therefore "twice critical", since it belongs to two critical branches.<br> Indeed, its critical behavior is different from that of a conventional