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vanishing, lines and vertical

NOTE. As a general ride, it is well to assume the station point on a vertical line half way between two lines dropped from the extreme edges of the diagram, as indicated. This is not necessary, but, as will be explained later, it usually insures a more pleasing perspective projection.

Next find the vanishing points for the different systems of lines in the object ( 12). There are three systems of lines in the block, formed by its three sets of parallel edges. ' 1st. A system formed by the four horizontal edges vanishing to the right: ab, ef, dc, and leg.

2d. A system formed by the four horizontal edges vanishing towards the left: ad, ek, be, and fg.

3d: A system formed by the four vertical edges.

First find the vanishing point for the system parallel to ab by drawing through the station point a line parallel to ab and finding where it the picture plane (24 g). A" drawn through SP" is the horizontal projection of such a line. Its ver tical projection (Av), drawn through SF", will coincide with VH, and its vanishing point will be found on VH at vab ( 51). All

lines in the perspective of the object that are parallel to ab will meet at Val 24 a). In a similar manner find v'', which will be the vanishing point for all lines parallel to ad.

54. If the method for finding any vanishing point is applied to the system of vertical lines, it will be found that this vanishing point will lie vertically over SPv at infinity. That is to say, since all vertical lines are parallel to the picture plane, if a ver tical line is drawn through the station point, it will never pierce the picture plane. Therefore (24 g), the perspective of the van ishing point of a vertical line cannot be found within any finite limits, but will be vertically over SP r, and at an infinite distance from it. In a perspective Projection all vertical lines are drawn actually vertical, and not converging towards one another. ;