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ZENITH AND NADIR
A. Spherical Projection. Blue equatorial and orange meridional planes.
B. Dark blue plane describes a circle on the sphere. C. Lines forming
cones on the stereographic net. D and E illustrate the derivation of lower
hemisphere projection by joining traces of planes on the hemisphere with
zenith and the cyclographic traces or great circles on the projection. MERIDIONAL PLANE A plane that contains zenith and nadir both and is orthogonal to the
equator in spherical projection is called the meridional plane. The orange
plane in A and B parts of the figure is the meridional plane.
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