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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #1  
Old 07-30-2011
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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)?
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Old 07-30-2011
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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.
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Old 07-30-2011
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I tried it with max sea with vector maps and the route is great circle.
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Old 07-30-2011
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It's going to depend on how your particular navigation program is set up.
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Old 07-30-2011
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I just checked Garmin's website and they state that
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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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