On Wed, 19 Jun 2013 18:56:22 -0400, "Eisboch" wrote:
wrote in message ...
On Wed, 19 Jun 2013 11:07:36 -0500, wrote:

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'm not all that familiar with Garmin units or that feature but lets
do a little thought experiment and see if we can figure it out. If
it is going to create a new waypoint at 90 degrees, wouldn't that be
at 90 degrees to your present course-over-ground (COG)? If so, the
new waypoint would be on your present latitude only if your COG was
due north (0 degrees true) or due south (180 degrees true). Am I
missing something? Is your unit set up to report directions as "true"
or "magnetic"? If magnetic, that would account for your discrepency.

----------------------------------------

Does that Garmin navigation system have an input from a fluxgate
compass on the boat as well as receiving the satellite data?

No, I'm using a simple handheld Garmin 76Map maybe 10 years old. And
the projection feature doesn't use either compass or satellites to do
the projection calculation. Doesn't even matter if the unit is in
simulation mode, it can still do the calculation. It's a fairly
standard feature on Garmin handhelds as well as lower end fixed mount
Garmins. I'm not very familiar with high end Garmin units or other
manufacturers but I would guess it would be standard with them too.
You plug in a location (lat/lon), then plug in a distance and bearing.
It instantly gives you the projected Lat/Lon.

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.

--
Sir Gregory

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.

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...

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.

If you correct for deviation your course heading will be 090 true.

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.

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 :-)

On 6/19/2013 10:39 PM, Hank© 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.

If you correct for deviation your course heading will be 090 true.

Is there a static equation for that?

On 6/19/2013 10:50 PM, JustWaitAFrekinMinute wrote:
On 6/19/2013 10:39 PM, Hank© 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.

If you correct for deviation your course heading will be 090 true.

Is there a static equation for that?


Yeah.

East is least, west is best.

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.