In Fig. 32, the dotted line BD, drawn to the point of distance D, is at an angle of 45° to the base AG. It will be seen that the line BV´ is at a greater angle to the base than BD; it is therefore drawn to a point V´, within the point of distance and nearer to the point of sight S. On the other hand, the line BV´´ is at a more acute angle, and is therefore drawn to a point some way beyond the other distance point.
Note.—When this vanishing point is a long way outside the picture, the architects make use of a centrolinead, and the painters fix a long string at the required point, and get their perspective lines by that means, which is very inconvenient. But I will show you later on how you can dispense with this trouble by a very simple means, with equally correct results.
[Rule 8]
Lines which incline upwards have their vanishing points above the horizontal line, and those which incline downwards, below it. In both cases they are on the vertical which passes through the vanishing point (S) of their horizontal projections.
Fig. 33.
This rule is useful in drawing steps, or roads going uphill and downhill.