Home |
Search |
Today's Posts |
|
London Transport (uk.transport.london) Discussion of all forms of transport in London. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
|
#1
|
|||
|
|||
Technology for its own sake?
"James Christie" wrote in message ... With difficulty, because GPS has an accuracy of +/- 100m, unless of course you are using Differential GPS, but that is mainly a maritime system. -- It's been somewhat better than that for a while, since the "random error" was removed. IME the error is probably nearer 2 metres. Though the powers that be can reintroduce the random factor, or turn it off entirely, should they feel the need. G |
#2
|
|||
|
|||
Technology for its own sake?
On Thu, 23 Sep 2004 18:25:33 UTC, "Gavin Hamilton"
wrote: : It's been somewhat better than that for a while, since the "random error" : was removed. IME the error is probably nearer 2 metres. Though the powers : that be can reintroduce the random factor, or turn it off entirely, should : they feel the need. You have to be careful not to confuse the random precison errors with the unrandom accuray ones. Civilian GPS is designed to be precise to about +/- 10m, whereas military GPS, which uses different signals, is precise to +/- 1m. Those errors are random - there is nothing you can do about them. Selective availability was a deliberate degradation of accuracy, done by effectively instructing satellites to tell porkies in their signals, and thereby displace all GPS positions in a particular area by an ordained amount. That's what doesn't happen (much) any more, but the precision errors remain. Ian -- |
#3
|
|||
|
|||
Technology for its own sake?
"Ian Johnston" wrote in message news:cCUlhtvFIYkV-pn2-KSqR179sj7HU@localhost... You have to be careful not to confuse the random precison errors with the unrandom accuray ones. Civilian GPS is designed to be precise to about +/- 10m, whereas military GPS, which uses different signals, is precise to +/- 1m. Those errors are random - there is nothing you can do about them. Selective availability was a deliberate degradation of accuracy, done by effectively instructing satellites to tell porkies in their signals, and thereby displace all GPS positions in a particular area by an ordained amount. That's what doesn't happen (much) any more, but the precision errors remain. I have experienced an distinct improvement in accuracy over the last few years but I am also aware that in certain circumstances GPS is not to be relied upon. Such events occur, for example, in narrow valleys where the signals can be "deflected" for want of a better description so GPS wouldn't work very well in cuttings - or tunnels for that matter. SA would not be very effiective if all satellites were to displace their positions by the same amount in the same direction - AFAIK each satellite had its own displacement which was random - watching a GPS position on a chart plotter was quite interesting in those days. Now the position doesn't move and will even plot a position on the correct side of a pontoon. However when the authorities are playing silly b*ggers with the signal it tends to be anounced in navigation warnings..... G |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
London Underground has its own binmen | London Transport | |||
TfL acknowledges contactless technology risk | London Transport | |||
London Underground gate revenue protection technology | London Transport | |||
New National Security Technology ignored that might have stopped the bombing | London Transport | |||
East London Extension now has its own website | London Transport |