simple GPS lat/lon display?

On 2008-04-07, clifto <[email protected]> wrote:
> Richard B. Gilbert wrote:
>> clifto wrote:
>>> News wrote:
>>>>clifto wrote:
>>>>>Kurt wrote:
>>>>>>"Richard B. Gilbert" <[email protected]> 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

---

› See More: simple GPS lat/lon display?

Dennis Ferguson wrote:
> On 2008-04-07, clifto <[email protected]> wrote:
>
>>Richard B. Gilbert wrote:
>>
>>>clifto wrote:
>>>
>>>>News wrote:
>>>>
>>>>>clifto wrote:
>>>>>
>>>>>>Kurt wrote:
>>>>>>
>>>>>>>"Richard B. Gilbert" <[email protected]> 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.

News wrote:

> Dennis Ferguson wrote:
>> On 2008-04-07, clifto <[email protected]> wrote:
>>
>>>Richard B. Gilbert wrote:
>>>
>>>>clifto wrote:
>>>>
>>>>>News wrote:
>>>>>
>>>>>>clifto wrote:
>>>>>>
>>>>>>>Kurt wrote:
>>>>>>>
>>>>>>>>"Richard B. Gilbert" <[email protected]> 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.

Except that the specs they show are with the old SA settings, not the
current zero setting.

--
Dutch

Dutch wrote:
> News wrote:
>
>
>>Dennis Ferguson wrote:
>>
>>>On 2008-04-07, clifto <[email protected]> wrote:
>>>
>>>
>>>>Richard B. Gilbert wrote:
>>>>
>>>>
>>>>>clifto wrote:
>>>>>
>>>>>
>>>>>>News wrote:
>>>>>>
>>>>>>
>>>>>>>clifto wrote:
>>>>>>>
>>>>>>>
>>>>>>>>Kurt wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>>"Richard B. Gilbert" <[email protected]> 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.
>
>
> Except that the specs they show are with the old SA settings, not the
> current zero setting.
>


Correct, which voids the OP's accuracy and error probabilities.

News <[email protected]> wrote in
news:[email protected]:

> Correct, which voids the OP's accuracy and error probabilities.
>
>

With the zero setting, and the fix not moving around constantly, the
accuracy of GPS is most dependent on having a clear view of the majority of
the satellites with minimal multipath propagation caused by high buildings,
bridges, mountains, towers and anything else reflecting the incoming
signal.

In a clear parking lot, with more than 6 satellites in direct view, it will
place the GPS in its location in a single parking space with no multipath
in flat country. In city canyons of high rise buildings where the actual
direct view of the sky is only a few degrees in most directions, you're
lucky if it stops going crazy in the area of the whole aforementioned
parking lot at the mall. It'll be all over the place as you move around,
even walking and really screwing it with multipath going in a dozen
directions at once.

GPS is very dependent on TIMING, the time it takes the signal to get from
the precisely transmitting bird to your receiver's fixed delay.
http://electronics.howstuffworks.com/gps.htm
This website does a great job, in a series of sections, to show how GPS
works and that TIMING is EVERYTHING in the GPS system. The text is nicely
detailed without becoming the math monster of spherical trig the scientific
websites quickly become. Just take the calculations for granted.

It's really quite neat how the cheap GPS gets an atomic reference clock for
free (displaying it on your screen, quite handily).

To really see what TIMING means to your GPS accuracy with awful multipath
making the paths from the birds go crazy, just take your GPS mapping box
into an open restaurant with a metal roof to block out the direct signals
and large windows on at least 2 sides so the signals can bounce around off
the traffic, buildings, etc., the GPS can see through the window. Move
away from the windows far enough so you cannot see the sky from your table.
Sit, eat, and watch the crazy patterns of a system gone mad.....

Larry wrote:

> News <[email protected]> wrote in
> news:[email protected]:
>
>> Correct, which voids the OP's accuracy and error probabilities.
>
> With the zero setting, and the fix not moving around constantly, the
> accuracy of GPS is most dependent on having a clear view of the majority of
> the satellites with minimal multipath propagation caused by high buildings,
> bridges, mountains, towers and anything else reflecting the incoming
> signal.
>
> In a clear parking lot, with more than 6 satellites in direct view, it will
> place the GPS in its location in a single parking space with no multipath
> in flat country. In city canyons of high rise buildings where the actual
> direct view of the sky is only a few degrees in most directions, you're
> lucky if it stops going crazy in the area of the whole aforementioned
> parking lot at the mall. It'll be all over the place as you move around,
> even walking and really screwing it with multipath going in a dozen
> directions at once.
>
> GPS is very dependent on TIMING, the time it takes the signal to get from
> the precisely transmitting bird to your receiver's fixed delay.
> http://electronics.howstuffworks.com/gps.htm
> This website does a great job, in a series of sections, to show how GPS
> works and that TIMING is EVERYTHING in the GPS system. The text is nicely
> detailed without becoming the math monster of spherical trig the scientific
> websites quickly become. Just take the calculations for granted.
>
> It's really quite neat how the cheap GPS gets an atomic reference clock for
> free (displaying it on your screen, quite handily).
>
> To really see what TIMING means to your GPS accuracy with awful multipath
> making the paths from the birds go crazy, just take your GPS mapping box
> into an open restaurant with a metal roof to block out the direct signals
> and large windows on at least 2 sides so the signals can bounce around off
> the traffic, buildings, etc., the GPS can see through the window. Move
> away from the windows far enough so you cannot see the sky from your table.
> Sit, eat, and watch the crazy patterns of a system gone mad.....

That's where "assisted GPS" (aGPS), as used on many cell phones like my
V3m helps out. By getting much of the satellite data via the cell signal
using data from the tower's GPS, the accuracy is enhanced, even within
buildings or other situations where the sat signals are partially
obstructed. Your location is also pinpointed much faster, since a lot of
the computations are handled by external computers instead of in the
handset. It's still much more accurate outside in the clear of course...

--
Dutch

Dennis Ferguson wrote:
> 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."

Missed that. Cranial flatulence. Thanks.

--
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