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brokesailor 07-30-2011 07:43 AM

Great circle course
If you plot a course between two distant points on a GPS using vector charts is this the great circle route (shortest route)?

Zanshin 07-30-2011 08:22 AM

No, it is not a great circle route. Usually the GPS plotted course will have one compass course for the whole trip, whereas a great circle route has changes in compass course. If your course is N-S or less than a thousand miles, the distance differences are going to be less than those imposed by making one or two bad tacks.

celenoglu 07-30-2011 09:53 AM

I tried it with max sea with vector maps and the route is great circle.

PBzeer 07-30-2011 10:19 AM

It's going to depend on how your particular navigation program is set up.

Zanshin 07-30-2011 10:58 AM

I just checked Garmin's website and they state that

GPS normally uses great circle calculations for distance and desired track.
On an east-west crossing 90 degrees of longitude (1/4 of the earth's circumference) at around 20 degrees N, the difference between rhumb line and great circle is 124Km on a distance of 8166km. The difference at the equator is 0 but at higher latitudes it makes more of a difference.

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