Suppose, we have two pairs of plane coordinates with one common pair, so we got two segments with one common point. We can calculate tangent for each segment to compare similarity of their angle (how small the delta of tangents).
When we turn to spheroid, and got two pairs of (lat, lon) GPS coordinates, also with one common point, and we got arcs instead of plain segments,
What equivalent measure should i use to check angle similarity, and how can i calculate it?
I need to know how "near" is one arc to another (or how small is the angle they make, because they have a common point)
An answer is related to Great-circle_navigation
The equivalent of plane tangent is a tangent of angle (π/2 - α0) in figures 1 and 2, i.e. an angle between an arc and equator. The difference between two tangents of two arcs will show how "near" is one arc to another