On a recent trip to Florida, my 2360 frequently reported that we were
below sea level. I can understand such a report when in New Orleans, or
anywhere you're surrounded by levees. But on the Florida Keys highway,
there are no levees.

I'm showing points from the track below.
Can someone please explain this?

Dave S.

481 11/11/2011 4:58:01 PM -33 ft 6 m 0:00:01 22 km/h 331° true N24
39.559 W81 16.481
482 11/11/2011 4:58:02 PM -31 ft 6 m 0:00:01 21 km/h 331° true N24
39.561 W81 16.483
483 11/11/2011 4:58:03 PM -28 ft 6 m 0:00:01 22 km/h 6° true N24
39.564 W81 16.485
484 11/11/2011 4:58:04 PM -26 ft 5 m 0:00:01 19 km/h 16° true N24
39.567 W81 16.484
485 11/11/2011 4:58:05 PM -26 ft 5 m 0:00:01 17 km/h 17° true N24
39.570 W81 16.484
486 11/11/2011 4:58:06 PM -28 ft 2 m 0:00:01 8 km/h 61° true N24
39.573 W81 16.483
487 11/11/2011 4:58:07 PM -30 ft 4 m 0:00:01 15 km/h 64° true N24
39.573 W81 16.481
488 11/11/2011 4:58:08 PM -31 ft 5 m 0:00:01 17 km/h 61° true N24
39.574 W81 16.479
489 11/11/2011 4:58:09 PM -33 ft 45 m 0:00:07 23 km/h 62° true N24
39.575 W81 16.477
490 11/11/2011 4:58:16 PM -41 ft 7 m 0:00:01 25 km/h 63° true N24
39.587 W81 16.453
491 11/11/2011 4:58:17 PM -42 ft 31 m 0:00:08 14 km/h 62° true N24
39.588 W81 16.449
492 11/11/2011 4:58:25 PM -48 ft 31 m 0:00:05 22 km/h 61° true N24
39.596 W81 16.433
493 11/11/2011 4:58:30 PM -48 ft 6 m 0:00:01 20 km/h 62° true N24
39.604 W81 16.417
494 11/11/2011 4:58:31 PM -47 ft 7 m 0:00:01 27 km/h 11° true N24
39.606 W81 16.414
495 11/11/2011 4:58:32 PM -45 ft 12 m 0:00:07 6 km/h 0° true N24
39.610 W81 16.413
496 11/11/2011 4:58:39 PM -42 ft 13 m 0:00:02 23 km/h 23° true N24
39.616 W81 16.413
497 11/11/2011 4:58:41 PM -42 ft 5 m 0:00:01 18 km/h 71° true N24
39.623 W81 16.410
498 11/11/2011 4:58:42 PM -41 ft 7 m 0:00:01 25 km/h 70° true N24
39.623 W81 16.407
499 11/11/2011 4:58:43 PM -41 ft 71 m 0:00:06 43 km/h 70° true N24
39.625 W81 16.403
500 11/11/2011 4:58:49 PM -36 ft 162 m 0:00:09 65 km/h 68° true N24
39.638 W81 16.364
501 11/11/2011 4:58:58 PM -31 ft 245 m 0:00:11 80 km/h 65° true N24
39.670 W81 16.275
502 11/11/2011 4:59:09 PM -34 ft 369 m 0:00:15 89 km/h 64° true N24
39.725 W81 16.143
503 11/11/2011 4:59:24 PM -42 ft 585 m 0:00:23 92 km/h 64° true N24
39.812 W81 15.946
504 11/11/2011 4:59:47 PM -48 ft 659 m 0:00:26 91 km/h 64° true N24
39.950 W81 15.634
505 11/11/2011 5:00:13 PM -50 ft 343 m 0:00:14 88 km/h 66° true N24
40.106 W81 15.282
506 11/11/2011 5:00:27 PM -45 ft 357 m 0:00:16 80 km/h 65° true N24
40.181 W81 15.097
507 11/11/2011 5:00:43 PM -45 ft 377 m 0:00:17 80 km/h 62° true N24
40.262 W81 14.905

On 12/08/2011, DaveS posted:
> On a recent trip to Florida, my 2360 frequently reported that we were below
> sea level. I can understand such a report when in New Orleans, or anywhere
> you're surrounded by levees. But on the Florida Keys highway, there are no
> levees.

> I'm showing points from the track below.
> Can someone please explain this?

GPS devices are notoriously bad at determining altitude.

--
Gene E. Bloch (Stumbling Bloch)

Op 9-12-2011 0:49, Gene E. Bloch wrote:
> On 12/08/2011, DaveS posted:
>> On a recent trip to Florida, my 2360 frequently reported that we were
>> below sea level. I can understand such a report when in New Orleans,
>> or anywhere you're surrounded by levees. But on the Florida Keys
>> highway, there are no levees.
>
>> I'm showing points from the track below.
>> Can someone please explain this?
>
> GPS devices are notoriously bad at determining altitude.
>

Even if you're not moving at all, the altitude will go up and down as if
you're riding a roller-coaster :-)
--

Cheerio,
Rudolpho
Carpe diem

In news:(E-Mail Removed) Gene E. Bloch
<(E-Mail Removed)> wrote:

> On 12/08/2011, DaveS posted:
>> On a recent trip to Florida, my 2360 frequently reported that we were
>> below sea level. I can understand such a report when in New Orleans,
>> or anywhere you're surrounded by levees. But on the Florida Keys
>> highway, there are no levees.
>
>> I'm showing points from the track below.
>> Can someone please explain this?
>
> GPS devices are notoriously bad at determining altitude.

Besides, isn't GPS altitude (including the idea of what "sea level" is)
based on the mathematical model of the earth that's in use at the
instant?

Your GPSR really has no idea of what the ocean is doing.

--
(E-Mail Removed) St. Paul, MN

Bert wrote:
> In news:(E-Mail Removed) Gene E. Bloch
> <(E-Mail Removed)> wrote:
>
>> On 12/08/2011, DaveS posted:
>>> On a recent trip to Florida, my 2360 frequently reported that we
>>> were below sea level. I can understand such a report when in New
>>> Orleans, or anywhere you're surrounded by levees. But on the
>>> Florida Keys highway, there are no levees.
>>
>>> I'm showing points from the track below.
>>> Can someone please explain this?
>>
>> GPS devices are notoriously bad at determining altitude.
>
> Besides, isn't GPS altitude (including the idea of what "sea level"
> is) based on the mathematical model of the earth that's in use at the
> instant?

My guess it's based on the number of satellites it's getting a feed from at
the time - the more it can see the more accurate the display.

On 12/09/2011, Rudolpho posted:
> Op 9-12-2011 0:49, Gene E. Bloch wrote:
>> On 12/08/2011, DaveS posted:
>>> On a recent trip to Florida, my 2360 frequently reported that we were
>>> below sea level. I can understand such a report when in New Orleans,
>>> or anywhere you're surrounded by levees. But on the Florida Keys
>>> highway, there are no levees.
>>
>>> I'm showing points from the track below.
>>> Can someone please explain this?
>>
>> GPS devices are notoriously bad at determining altitude.
>>

> Even if you're not moving at all, the altitude will go up and down as if
> you're riding a roller-coaster :-)

That explains my dizziness!

Thanks for the smile.

BTW, I should have added to my post that the OP's altitude readings
actually looked pretty good compared to what I often see.

--
Gene E. Bloch (Stumbling Bloch)

On 12/09/2011, Tom J posted:
> Bert wrote:
>> In news:(E-Mail Removed) Gene E. Bloch
>> <(E-Mail Removed)> wrote:
>>
>>> On 12/08/2011, DaveS posted:
>>>> On a recent trip to Florida, my 2360 frequently reported that we
>>>> were below sea level. I can understand such a report when in New
>>>> Orleans, or anywhere you're surrounded by levees. But on the
>>>> Florida Keys highway, there are no levees.
>>>
>>>> I'm showing points from the track below.
>>>> Can someone please explain this?
>>>
>>> GPS devices are notoriously bad at determining altitude.
>>
>> Besides, isn't GPS altitude (including the idea of what "sea level"
>> is) based on the mathematical model of the earth that's in use at the
>> instant?

> My guess it's based on the number of satellites it's getting a feed from at
> the time - the more it can see the more accurate the display.

That's really a separate issue.

Bert is referring to the altitude that the GPS considers correct[1],
and you are referring to the errors in measuring that value.

[1] That's what the term "mathematical model" refers to.

--
Gene E. Bloch (Stumbling Bloch)

On Fri, 9 Dec 2011 12:24:17 -0500, "Tom J" <(E-Mail Removed)>
wrote:

>Bert wrote:
>> In news:(E-Mail Removed) Gene E. Bloch
>> <(E-Mail Removed)> wrote:
>>
>>> On 12/08/2011, DaveS posted:
>>>> On a recent trip to Florida, my 2360 frequently reported that we
>>>> were below sea level. I can understand such a report when in New
>>>> Orleans, or anywhere you're surrounded by levees. But on the
>>>> Florida Keys highway, there are no levees.
>>>
>>>> I'm showing points from the track below.
>>>> Can someone please explain this?
>>>
>>> GPS devices are notoriously bad at determining altitude.
>>
>> Besides, isn't GPS altitude (including the idea of what "sea level"
>> is) based on the mathematical model of the earth that's in use at the
>> instant?
>
>My guess it's based on the number of satellites it's getting a feed from at
>the time - the more it can see the more accurate the display.
>

The error, less than 50 ft, is miniscule, anyway.

http://gpsinformation.net/main/altitude.htm

Op 9-12-2011 15:38, Bert wrote:
> In news:(E-Mail Removed) Gene E. Bloch
> <(E-Mail Removed)> wrote:
>
>> On 12/08/2011, DaveS posted:
>>> On a recent trip to Florida, my 2360 frequently reported that we were
>>> below sea level. I can understand such a report when in New Orleans,
>>> or anywhere you're surrounded by levees. But on the Florida Keys
>>> highway, there are no levees.
>>
>>> I'm showing points from the track below.
>>> Can someone please explain this?
>>
>> GPS devices are notoriously bad at determining altitude.
>
> Besides, isn't GPS altitude (including the idea of what "sea level" is)
> based on the mathematical model of the earth that's in use at the
> instant?

I have a digital map on my Ipad2 which shows everything below sealevel
in blue (water) when you switch to the mathematical mode :-)
Large parts op Holland, Belgium, Germany ar flooded on that map
--

Çheerio,
Rudolpho
Carpe diem

Rudolpho wrote:
> I have a digital map on my Ipad2 which shows everything below sealevel
> in blue (water) when you switch to the mathematical mode :-)
> Large parts op Holland, Belgium, Germany ar flooded on that map

Global warming, here we come...

Mike.
--
If reply address is Mike@@mjcoon.+.com (invalid), remove spurious "@"
and substitute "plus" for +.