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#1
posted to rec.boats.cruising,rec.boats
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Navigation question (Projecting a waypoint w/GPS)
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... Using a Garmin's Waypoint Projection feature, and projecting a waypoint at 90 degrees, shouldn't my projected waypoint end up on the same latitude as the original? And if not, why not? For example, beginning at 30 degrees N latitude and 89 degrees W longitude, I project a new waypoint at a distance of 10 miles with a bearing of 90 degrees. As expected, my projected longitude changes to a point further east. But for some reason, the projected latitude ends up at a higher latitude than 30 degrees. In my example, the projected latitude ends up as 30 degrees, 23.866 Minutes North. I've tried using the same example on 3 different Garmins with the same result. What am I missing? It's the great circle conundrum. Charts aren't a fair representation of the surface of the Earth. -- Sir Gregory |
#2
posted to rec.boats.cruising,rec.boats
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Navigation question (Projecting a waypoint w/GPS)
On Wed, 19 Jun 2013 15:00:45 -0400, " Sir Gregory Hall, Esq·"
åke wrote: Charts aren't a fair representation of the surface of the Earth. === That's true but it does not relate to this particular issue. |
#3
posted to rec.boats.cruising,rec.boats
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Navigation question (Projecting a waypoint w/GPS)
wrote in message
... On Wed, 19 Jun 2013 15:00:45 -0400, " Sir Gregory Hall, Esq·" åke wrote: Charts aren't a fair representation of the surface of the Earth. === That's true but it does not relate to this particular issue. It is too true. The lines of latitude show as parallel on a Mercator projection chart while on a sphere (like the Earth) these lines are NOT parallel as the surface of the Earth is not flat but spherical. Ask yourself this question: The longitudinal lines everybody agrees are not parallel as they all run together at the poles and have maximum separation at the equator, but the *parallels* of latitude though parallel on the chart are NOT parallel on the sphere of the Earth. Thus the divergence noted on the Garmin plotter. A great circle route is actually a straight line across the Earth's surface but on a Mercator projection it shows as a curve. What makes you think the opposite isn't true? HTH. -- Sir Gregory |
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