If I measure a line from point (A) to point (B) Google Earth gives me a heading. if I measure a line from B to A I would think it should be 180 degrees from (A) to (B). It is not. I'm trying to find the angles of a triangle drawn on Google Earth and the variation is making it difficult.
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1Angles are complicated on a sphere, and even more so on a spheroid.– VinceNov 26, 2018 at 13:44
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There's some information here.– mkennedyNov 26, 2018 at 23:09
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2 Answers
Technically, because the line is an orthodrome, not a loxodrome.
Google Earth measures the shortest curved distance between both points. The shortest curved line between two points is a variable heading line. Basically, it satisfies that the cosine of the true curse multiplied by the cosine of the latitude, at any point of a great circle, is a constant. Source
Therefore, that line has different orientations in its initial and final point. When measuring in one direction or another, Google Earth is showing you the heading at the beginning of the line, but the starting point of the measurements is being exchanged.
This has nothing to do with seeing it as a straight line. Measurements on Google Earth should not be seen as straight lines (however the loxodromes do).
To calculate the internal angles of a spherical triangle, there are some interesting theorems in spherical trigonometry that could help you.
answered Feb 1, 2019 at 20:37
"Heading" means, which direction on the compass your line is pointing to. A at the equator, B at the north pole would mean heading = 0, vice versa heading = 180.
