Navigation question (Projecting a waypoint w/GPS)
 

wrote in message
...
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

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.

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