What is the delta between two lat/lon pairs called? Delta degrees? Arcs?
Is it some quantity of distance but what is its unit of measurement?
And related: Can we use pythagoras to calculate this distance?
eg. d = (0, 3) and (4, 0) = 5?
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Sign up to join this communityYou can't use the simple Pythagorean theorem as that one's for planes whereas the distances you are talking about now are on a curve. For that, you'll have to use spherical trigonometry. From Wikipedia:
Let
be the geographical latitude and longitude of two points (a base "standpoint" and the destination "forepoint"), respectively, and
their absolute differences; then
, the central angle between them, is given by the spherical law of cosines:
The distance d, i.e. the arc length, for a sphere of radius r and
given in radians, is then
Note that using r = 6,371.009 metres is appropriate for calculating great-circle distances between points on the Earth's surface, in which case the result d will also be in metres.
It's called a great circle distance btw.
I've seen a Euler Pole plus an angular displacement used to describe "delta". This is used a lot in plate reconstruction, where these deltas are often referred to as "rotations", but I'm not sure if that is a formal definition.