Fixed Radii
The following radii are fixed and do not include a variable location dependence. They are derived from the WGS-84 ellipsoid.
The value for the equatorial radius is defined to the nearest 0.1 meter in WGS-84. The value for the polar radius in this section has been rounded to the nearest 0.1 meter, which is expected to be adequate for most uses. Please refer to the WGS-84 ellipsoid if a more precise value for its polar radius is needed.
The radii in this section are for an idealized surface. Even the idealized radii have an uncertainty of ± 2 meters. The discrepancy between the ellipsoid radius and the radius to a physical location may be significant. When identifying the position of an observable location, the use of more precise values for WGS-84 radii may not yield a corresponding improvement in accuracy.
The symbol given for the named radius is used in the formulae found in this article.
Read more about this topic: Earth Radius
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