Smart, Edward Howard · London : Macmillian and Co. · leaf 125
In projecting a circle, some straight line in the plane of thecircle is projected to infinity. This is the vanishing line ofthe plane. We have to consider three cases : (1) The vanishing line cuts the circle in real points. (2) „ „ touches the circle. (3) „ „ cuts the circle in imaginary points.… … Fig. 47. In two opposite (parallel) sides of a cardboard box cut apair of equal circular holes. Place a source of light (the more P.O. o 98 PROJECTIVE GEOMETRY nearly approximating to a point source the better) at themiddle point of the line joining the centres of the holes. A double oblique cone…
Geometry, Projective
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