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Is spherical trig still a thing? Calculation is so cheap now. If you want to find the spherical distance between cities from first principles, it's easiest to convert to 3D rectangular coordinates and find the angle ABC from the vector dot product, where A and C are the cities and B is the center of the earth. Same for other types of navigational calculations like headings. But, I've never looked into it really.

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Yep, it's mostly used in for navigation, especially as a backup in case GPS fails (in the case of a lightning strike on a sailboat, for instance, probably all your electronics are toast). The military still uses it with slide rules/log tables, in case of jamming, etc. It kind of "disappeared" sometime after WWII, and there aren't many new books on it, but you'll see it come up in computer graphics and animation quite a bit, and I'm pretty sure it's used extensively in surveying still.

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