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Vic Fraenckel wrote:
>
> My routines give the azimuth (referenced to true north) of the second point
> from the first point (and the azimuth from the second point to the first
> point - NOT recipricals on an ellipse).

Yes, that's what I figured you meant. I don't even know what a
reciprocal on an ellipse is. My point was that the Mercator methods
yield a rhumb line, which is easier to follow. You simply keep a
constant heading throughout the voyage. (I'm ignoring variation etc.
for simplicity.)

On the other hand, computing the azimuth from Point A to Point B
yields the initial heading for a great circle course. However, if the
vessel stays on that heading it will miss Point B. The miss may be
trivial or huge, depending on distance and the lat/lon of the points.

The rhumb line and great circle methods both have their place in the
navigator's arsenal.

   

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