CHAPTER I.

FUNDAMENTAL PRINCIPLES OF ICONOMETRY.

If only one perspective of an object, including its distance line, the principal point, and the horizon line is given—in other words, if the point of view and the central projection upon a vertical plane of an object are given—the object itself can not yet be determined regarding its position and dimensions. In the same way the géographie position of a point can not be located

Fto.l

by means of the plane table from a known station, nnless direct measurements to ascertain the distance of such point from the station are resorted to.

If, however, two different perspectives (including their éléments) of the same object, obtained from two different known stations, are given, the dimensions and the position of the object with reference to the two stations may be determined iconometrieally in à manner analogous to that in

Fig. Z

which a point is located (by intersection) on the plane-table sheet by being observed upon from two différent plane-table stations. *

Referring to fig. 1, the positions of the caméra stations A and A', also the distance A Amay be given, and two photographs containing the image t of an object T, including the image a1 of the other caméra station, may hâve been obtained from the two stations.

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