[Illustration: Fig. 15.]
Let the horizontal line _AB_ (Fig. 15.) be given in position and
magnitude. It is required to find its dividing-points.
Find the vanishing-point _V_ of the line _AB_.
With center _V_ and distance _VT_, describe circle cutting the
sight-line in _M_ and _N_.
Then _M_ and _N_ are the dividing-points required.
In general, only one dividing-point is needed for use with any
vanishing-point, namely, the one nearest _S_ (in this case the point
_M_). But its opposite _N_, or both, may be needed under certain
circumstances.