GPS - great circle or rhumb

ghostlymoron

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A question arose last night in the pub. Does a GPS or chart plotter give a great circle(shortest) or rhumb line course. No one was sure. I'm sure someone on the forum will know.
 

Salty John

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Some do one, some the other. To check what yours is, set a waypoint some large distance due east or west of you and press GOTO. If the course given is exactly 90 degrees or 270 degrees you're getting a rhumb line course, if it's, say, 220 degrees you're getting the initial course for a great circle route.
 

Salty John

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All the manufacturers may have standardised now, but on older sets it could be GC or Rhumb line.

In fact, GC routes were actually a series of rhumb line routes created by the set interjecting a number of waypoints between where you are and your GOTO destination - that still may be the case, the difference in distance would be tiny.

I learned this on a navigation course and I'm dredging it up from memory - I can't locate the course notes, and it was so long ago they were probably written on papyrus!
 
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