BoatBanter.com - View Single Post - Navigation question (Projecting a waypoint w/GPS)

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On Wed, 19 Jun 2013 16:08:19 -0400,
wrote:

On Wed, 19 Jun 2013 13:38:10 -0500, wrote:

Seems to me, whichever I use,
"due east" (or 90 degrees) should still mean never getting off the
lattitude where I started. Yes?/No?

===

No.

Due east magnetic will change your latitude unlees you are in a
location where declination equals zero (true = magnetic). Same with
due west of course.

hmmm.... Well, I had my "North Reference" originally set to "True". So
I changed it to "Magnetic" with a declination of zero and recalculated
my example. I ended up with a projected latitude that is different
than the "True" projection but still not the starting latitude of 30
degrees. This "Magnetic" projected latitude resulted in 30 degrees,
23.904 minutes North. That's dang close to the "True" projection but
not exact (rounding error maybe?) and still a far cry from the
original starting latitude of 30.

I'm slowly beginning to realize that, by following any particular
latitude all the way around the earth, you aren't actually traveling
due east or west unless you're following Latitude zero degrees (the
Equator). So maybe Garmin hasn't screwed up afterall (as I originally
suspected lol!).