04-08-2008, 12:45 AM
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 Re: simple GPS lat/lon display?
Dennis Ferguson wrote:
> On 2008-04-07, clifto <clifto@gmail.com> wrote:
>
>>Richard B. Gilbert wrote:
>>
>>>clifto wrote:
>>>
>>>>News wrote:
>>>>
>>>>>clifto wrote:
>>>>>
>>>>>>Kurt wrote:
>>>>>>
>>>>>>>"Richard B. Gilbert" <rgilbert88@comcast.net> wrote:
>>>>>>>
>>>>>>>
>>>>>>>>GPS, or at least the civilian version of it, is only accurate to within
>>>>>>>>about 300 feet or 100 meters.
>>>>>>>
>>>>>>>It's been changed for a few years, now more like 15 meters. Clinton was
>>>>>>>the one that changed that.
>>>>>>
>>>>>>http://www.navcen.uscg.gov/faq/gpsfaq.htm#Standard
>>>>>>
>>>>>>SPS provides accuracy's of (for position, the accuracy with respect to
>>>>>>geographic, or geodetic coordinates of the Earth) within:
>>>>>>100 meters (2 drms) horizontal 156 meters (2 Sigma) vertical 300 meters
>>>>>>(99.99% prob.) horizontal 340 nanoseconds time (95% prob.)
>>>>>
>>>>>"What is the status of Selective Availability (SA)?
>>>>
>>>>What does SA have to do with the 2008 accuracy specification I posted?
>>>
>>>IIRC, SA encrypted the low order bits in order to prevent GPS being used
>>>for weapons targeting and other anti-social behavior.
>>
>>That's true, but Clinton shut it off in 2001 and it hasn't been a problem
>>for nearly seven years now.
>
>
> Sure, but no one in the government said they wouldn't turn it back on if
> they felt like it which is why their SPS accuracy claims still always
> include the effects of SA.
>
> In fact the paragraph just above the accuracy specifications you quoted
> says, in part,
>
> "The SPS accuracy specifications, given below, include the effects of SA."
>
> which, I guess, is what SA has to do with the 2008 accuracy specification
> you posted.
>
> Dennis Ferguson
Bingo.  |