Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . platting is the stereographicprojection, in which the eye is supposed to be placed at thesurface of the sphere itself. Here, too, the visual rays divergemore and more toward the edges of the picture, but theyintersect it at greater angles than in the central projection,and even the outermost ray still strikes the plane of thepicture, so that this projection, too, permits the representationof a complete hemisphere. (Fig. 116, a.^ Finally, if the eye is plac
Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . platting is the stereographicprojection, in which the eye is supposed to be placed at thesurface of the sphere itself. Here, too, the visual rays divergemore and more toward the edges of the picture, but theyintersect it at greater angles than in the central projection,and even the outermost ray still strikes the plane of thepicture, so that this projection, too, permits the representationof a complete hemisphere. (Fig. 116, a.^ Finally, if the eye is placed outside of the sphere, but ata little distance, we obtain X.\\q extcrjialprojection {¥\g. 116, b)ywhich, however, is but very rarely used. To obtain an idea of the networks produced by theseperspective projections one has to take other things into con-sideration. If the eye-point, aside from its distance from the 4o8 MAP construction: terrestrial globe, lies in the axis of revolution of the earth, theprojection is called polar; if the eye-point lies in the plane ofthe equator, the projection is called equatorial; if the eye-point. Fig. ii6.—Stereographic {a) and External {b) Projections. lies outside the plane of the equator and outside the earthsaxis of revolution, the projection is called horizontal. Thus,
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