On Sat, 22 Jun 2013 18:54:33 -0400, " Sir Gregory Hall, Esq·"
åke wrote:

wrote in message
.. .
On Sat, 22 Jun 2013 16:23:37 +0000 (UTC), JohnF
wrote:

JohnF wrote:
wrote:
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.

Excuse me for following myself up, but either I'm totally confused
(a common occurrence) or that example's totally messed up...
You say your waypoint's distance is 10nm, but its latitude
changes by 23.866'. Heck, even if you headed exactly due north
for 10nm, latitude would only change by exactly 10'.

No, you're not confused. I'm just getting projected waypoints that
make no sense. Fortunately, so far, my unit's GPS capability is spot
on, so I can still use it to navigate (with backup). I just can't
trust the "Projection" feature for accurate results. Never used it
much anyway.
By the way, I tried projecting 10 miles due north and it changed my
latitude by 33' minutes. I'm done fiddling with it at this point.
Thanks for the come back tho.

Then you've got it set to magnetic north or it's stuck on magnetic
north no matter how you set it. Set it to true north and try it again.

It's been set on True for much of my experimenting. I think a bug is
stuck in there somewhere. lol! But I've now worked out the original
navigation problem that set me off on this whole brain frazzler in the
first place by using this calculator:

http://williams.best.vwh.net/gccalc.htm

It projected my waypoints within a few feet of where they are supposed
to be. I'll fiddle with my GPS calculator later. I'm overdue for a
new GPS anyway.

Thanks for the input.

I think this issue that has your point not ending up at the same north position could be resolved by plotting a waypoint at the same latitude but however far out you want it.

Then plot locations to reach that point on the line to the waypoint.

I'd bet you found that it worked slowly north to a point, then curved back south, to the waypoint. The further north you do this exercise, the more deviation from the starting and ending latitudes you'll find.

My two cents, anyway :{))

L8R

Skip

"Flying Pig" wrote in message
...
I think this issue that has your point not ending up at the same north
position could be resolved by plotting a waypoint at the same latitude but
however far out you want it.

Then plot locations to reach that point on the line to the waypoint.

I'd bet you found that it worked slowly north to a point, then curved back
south, to the waypoint. The further north you do this exercise, the more
deviation from the starting and ending latitudes you'll find.

My two cents, anyway :{))

L8R

Skip



Great circle and all that good stuff.. But, these Rubes just won't listen to
reason. No, I guess that's too much to expect.

--
SW
"Curses, foiled again!"

On Fri, 28 Jun 2013 16:54:34 -0700 (PDT), Flying Pig
wrote:
I think this issue that has your point not ending up at the same north position could be resolved by plotting a waypoint at the same latitude but however far out you want it.
Then plot locations to reach that point on the line to the waypoint.
I'd bet you found that it worked slowly north to a point, then curved back south, to the waypoint. The further north you do this exercise, the more deviation from the starting and ending latitudes you'll find.
My two cents, anyway :{))
L8R
Skip

I agree with what you're saying here. But I wasn't trying to find the
shortest distance between two points (the "great circle route"). My
problem had more to do with following a particular latitude (the
"great scenic route" :-)
Got it sorted out now though, thanks.