GPS Item

[poppi]

Something we have been keeping close tabs on here at our shop
Not new for some of you connected techies

   http://www.pcworld.com/businesscenter/article/165126/gps_system_could_begin_to_fail_within_a_year.html

  Looks like we'll see how things develop later this year

   Skip

[JackConrad]

What, NO GPS?  Now where did I that box of flares, I will be lost for sure!!  Jack

[poppi]

  I guess I will have to polish up the old tried and true methods....
    "Trust me dear we're not lost"
    " oh ALL right you can ask directions at the next feul up stop" (still have a 100 gals of feul left  )
    " Dear you have the map upside down?

  Seems I need to acquire some new tenants for where I am

Skip

[Dallas]

I know where I am.

[Sean]

The sky is falling!  The sky is falling!

This is old news, and, as usual, has been sensationalized by the media.  Not that I trust PCWorld to know what it is talking about in any case.  (And, to be clear, not a reflection on you, Skip -- I know you are just passing this along as an "FYI.")

The actual report is here:
http://www.gao.gov/products/GAO-09-670T

To clarify what "might" happen if the USAF does not get its act together, there will possibly be some degradation in positional accuracy, and, in particular, elevation.  So, IOTW, rather than having, say, 10-meter accuracy to which most of us have become accustomed since the retirement of "selective availability" during the Clinton administration, we might see a return to 30- or even 100-meter accuracy during brief periods until the constellation is beefed up.

This has a far greater impact, of course, on the military (who were never subject to selective availability) and, for example, land surveyors, who will have to leave their antennas in place for longer periods of time to get a more accurate fix.

The actual impact on civilian users of in-vehicle GPS receivers and chartplotters will be almost nil.  This subject, BTW, is also being beaten to death over in the boating community, where reliance on GPS chartplotters is now nearly universal.

-Sean
http://ourodyssey.blogspot.com

[cody]

My GPS (Granny Pointing System) is still operational and in reasonably good order, (I think) lol

[Tim Strommen]

The sky is falling!  The sky is falling!

This is old news, and, as usual, has been sensationalized by the media.  Not that I trust PCWorld to know what it is talking about in any case.  (And, to be clear, not a reflection on you, Skip -- I know you are just passing this along as an "FYI.")

Yes, and they failed to mention that many GPS chipset companies have for the last two years been ramping-up Galileo compatible GPS chips (and are available already).  In addition to the WAAS add-on for GPS, some of these new chips will use the second constellation for even better positioning accuracy in less time (I just bought a 65-channel 10Hz chip for $40 that can pick up GPS sat signals indoors - needs a PC though).

-Tim

[niles500]

And to think I gave my WAAS to my stepson thinking it was old useless tech -

[poppi]

land surveyors, who will have to leave their antennas in place for longer periods of time to get a more accurate fix.

Sorry but most survey protocall requires real time kinematic to be used and a minnimum of 3 sats. Selective availablity has
no bearing using RTK. If a sat quits in the middle of a survey the equipment automatically switches to another sat if available
and if PDOP or L2 degregates to much the surveyor may have to redo the collection. Increasing epics only helps to a point.

justa FWIW
  Skip

[Sean]

... most survey protocall requires real time kinematic to be used and a minnimum of 3 sats. Selective availablity has
no bearing using RTK. If a sat quits in the middle of a survey the equipment automatically switches to another sat if available
and if PDOP or L2 degregates to much the surveyor may have to redo the collection. Increasing epics only helps to a point.

I wasn't talking about selective availability... I was talking about the findings of the GAO report.  If there are "holes" in the constellation, you may need to leave the antenna in position for a longer period while the receiver waits for the needed number of birds to be visible.  The almanac, presumably, will still be accurate, and with a reasonable initial estimate of position and accurate clock, the receiver will generally know when it has a chance of acquiring the required signals.

For consumer receivers, this is much less of an issue.  For one, the precision requirement is different, but for another, the receiver is on all the time while it is being moved from position to position (unlike survey equipment, generally).  Four birds are required to obtain a 3-D "initial" fix, but once that fix has been computed by the receiver, brief drop-outs of constellation availability, wherein only two or three birds might be visible, will not cause the position to be lost.  The receiver generally dead reckons, by assuming that elevation is constant over short periods of time, and even that speed changes slowly if at all.

-Sean
http://ourodyssey.blogspot.com

[Nusa]

I agree with Sean, it's exaggerated by the press trying to make a story out of a possibility. The constellation needs 24 satellites for full service, and there's about 30 up there today, some of which are likely to fail soon. All they're saying is that this is a CHANCE that the number of functional GPS sats will drop slightly below 24 before replacements are sent up. And even if it does, it's only going to affect certain users, mostly those with special needs. The average civilian user would likely get adequate service with as few as 12 satellites in place.