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Can you expand on what the esoteric topic is and its application?

Translating between coordinate systems and basically anything that involves mapping and measuring in 3 dimensions on an irregular not-quite-spherical surface is really hard to get right.

I didn't make this picture, but it gives a good idea on the "irregular not-quite-spherical surface" part.

http://alienspacesciencenews.files.wordpress.com/2013/10/an-...

The Local Datum could be NAD83 or what-have-you based on where you are on the surface. Using the local datum gives better distance measurements and more accurately can represent elevation.

That's a pretty great image. I'll have to remember it for next time someone asks why is all this so hard and can't we just use WGS84 for everything.

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