[ale] WAY [OT] but geeky - how do I calibrate GPS barometric altimeter

[Pete Hardie]

Submarine?  Maybe you should just fix that leak? :)

Pete Hardie
--------
Better Living Through Bitmaps


On Tue, Feb 26, 2013 at 7:28 AM, Jim Lynch <ale_nospam at fayettedigital.com>wrote:

> On 02/25/2013 11:59 PM, Sean Kilpatrick wrote:
>
>>
>> The civilian rade GPS units by and large only claim to be accurate within
>> 50 feet or so -- in any direction. That certainly was proven true during a
>> recent trip to Amelia Island, Florida -- just north of Jacksonville.
>>
>> the unit reported elevation on different days between -50 and +75 feet,
>> when the car was parked ~maybe~ eight feet above mean high tide.
>>
>>  I agree, my sailboat varies from being a  submarine to a low flying
> aircraft when I'm on the water according to the gps.  Also the mathematical
> model of the earth GPSes us doesn't not accurately describe the actual
> surface of the earth.
>
> There are a number of surface models, including sphere oblate spheroid,
> ellipsoid, geoid and others.  Each has it's accuracies and inaccuracies.
>  To compound matters, the actual surface of the earth constantly changes
> its shape.
>
>
> It's best for hiking to use the altimeter as a relative measuring device.
>  "I am ascending" or "I am descending" or "This hill is 50 feet higher than
> my house".
>
> Jim.
> Jim.
>
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