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Syntax
Graticule
The graticule described is for a polar aspect.
Meridians: Equally spaced straight lines intersecting at the central pole. The angles displayed are true angles between meridians.
Parallels: Unequally spaced circles centered on the central pole. Spacing decreases away from this pole. The opposite hemisphere cannot be shown, nor can distant parts of the closer hemisphere. The limit of visibility depends on the observation altitude.
Poles: The central pole is a point. The other pole is not shown.
Features
This is a perspective projection on a plane tangent at the center point from a finite distance. Scale is true only at the center point, and is constant in the circumferential direction along any circle having the center point as its center. Distortion increases rapidly away from the center point, the only point which is distortion free. This projection is neither conformal nor equal area.
Parallels
The standard parallel contains the observation altitude above the surface in the same units as the geoid semi-major axis.
Remarks
This projection provides views of the globe resembling those seen from a spacecraft in orbit. The Orthographic projection is a limiting form with the observer at an infinite distance.
Limitations
This projection is available for the spherical geoid only. Data more distant than the limit of visibility is trimmed.
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