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Spherical coordinates

Earth Coordinates

Here I present the Earth-centered (ECEF) cartesian and spherical coordinates as well as local ENU coordinates. I also derive transformations between them.
Spherical coordinates

Great Circle

Here I derive the equation of the great circle on the spherical Earth, the formula for the shortest distance as well as other related formulas.
Torus

Torus

I derive equations of the torus and present an Octave program to draw it.