On 6/19/2013 11:38 PM, wrote:
On Wed, 19 Jun 2013 22:46:35 -0400, Hank©
wrote:

On 6/19/2013 10:31 PM, JustWaitAFrekinMinute wrote:
On 6/19/2013 10:29 PM, wrote:
On Wed, 19 Jun 2013 21:01:14 -0400, " Sir Gregory Hall, Esq·"
åke wrote:

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?

I suspect it's a matter of choosing the right Datum.
http://geography.about.com/od/geogra...n/a/datums.htm
The above should explain it well enough.
Your direction is only as accurate as the datum chosen.

My unit has 110 different Datums to choose from. So far, I've just
always used the Garmin default (WGS 84) for navigation and it has
always been fine for that. The waypoint projection feature is the only
thing that seems a bit squirrely. So if you have a datum
recommendation that might cure that, I'll be glad to give it a go.


Not following too closely but if you actually made the trip, does the
"target" destination come more into line as you get closer? If you know
what I mean...

The heading to destination will change as you get closer due to drift,
gps error, and compass error. The closer you get the more course error
will be introduced.

Hmmm..... I think I may have made this thread sound more complicated
than it actually is. This isn't about actual navigation. It's only
about a calculation that doesn't need GPS input. I don't know what
formula Garmin uses but I'm sure it can be done with a calculator or
computer. Maybe even a slide rule or an abacus :-)

If you turn off deviation compensation in your gps the results of a
waypoint projection should theoretically be as you expected unless
Garmin's algorithms are wrong.
If using the feature doesn't produce the desired result for you I
suggest you don't use that feature. If you need to know why that feature
behaves the way it does, you need to ask Garmin's software developers.