Form square ABCD (new method), produce sides BC and AD to the horizon at V, and produce VA to a· on base. Drop perpendicular from B to F the same length as a·B, and proceed as in the previous figure to find the eight points on the oblique square through which to draw the octagon.
Fig. 200.
It will be seen that this operation is very much the same as in parallel perspective, only we make our measurements on the base line a·B as we cannot measure the vanishing line BA otherwise.
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How to Draw an Octagonal Figure in Angular Perspective
In this figure in angular perspective we do precisely the same thing as in the previous problem, taking our measurements on the base line EB instead of on the vanishing line BA. If we wish to raise a figure on this octagon the height of EG we form the vanishing scale EGO, and from the eight points on the ground draw horizontals to EO and thus find all the points that give us the perspective height of each angle of the octagonal figure.