The vertical perspective projection is a map projection that corresponds to the appearance of a globe when directly viewed from some distance
away with the -axis of the viewer aligned parallel to the positive
-axis of the globe. It is given by the transformation equations
(1)
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(2)
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where
is the distance of the point of perspective in units of sphere radii and
(3)
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(4)
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Note that points corresponding to are on the back side of the globe and so should
be suppressed when making the projection.