I think it's 15m WITH the signal degradation. Without it (and some good kit) you should be able to get accuracy of around 1m. We used to use dGPS to achieve accuracy of 1m. dGPS (differential GPS - don't ask me for details, I just processed the data, not hack the code) uses base stations (whose coordinates are known) to compensate for the error introduced into the signal.
With the error in the signal, the output from a stationary GPS receiver will exhibit what looks like random movement within a given radius (8m or whatever). If you have several fixed receivers you can work out the errors introduced and subtract that error from an unfixed(?) receiver. Ie. One that's moving around, eg. a boat at sea.
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I think it's 15m WITH the signal degradation. Without it (and some good kit) you should be able to get accuracy of around 1m. We used to use dGPS to achieve accuracy of 1m. dGPS (differential GPS - don't ask me for details, I just processed the data, not hack the code) uses base stations (whose coordinates are known) to compensate for the error introduced into the signal.
With the error in the signal, the output from a stationary GPS receiver will exhibit what looks like random movement within a given radius (8m or whatever). If you have several fixed receivers you can work out the errors introduced and subtract that error from an unfixed(?) receiver. Ie. One that's moving around, eg. a boat at sea.
Or something like that.