Hikin_Jim wrote:jfr wrote:From the
wikipedia article: "Two different encodings are used: a public encoding that enables lower resolution navigation, and an encrypted encoding used by the U.S. military."
Is that still current? I know that when GPS first came out, they had a "futzing" routine that only military GPS receivers could de-crypt. But some clever civilians figured out some way to "average" (or something like that) the signals so that they could get a more accurate reading. The military then removed the "futzing" figuring that any sophisticated adversary could do what the civilians had done and that encryption was therefore pointless.
Jim, you're thinking of Selective Availability. This "futzing" was the deliberate degradation of the satellite signals in a manner (the addition of a pseudorandom signal) that only the military could characterize (via knowledge of the seed of the pseudorandom sequence) and reverse.
Selective Availability is
no longer active. And will likely not be active again for the reason you note. The "averaging" you refer to is actually the technique known as Differential GPS (DGPS).
As far as I know the only factors currently limiting the accuracy of civilian GPS receivers are the inherent limitations of the GPS system. But there are some
good solutions to addressing these limitations. Those civilian users willing to pay for units employing these techniques (geologists, surveyors, precision farmers) can enjoy centimeter-level accuracies.
Zip, unless you're both really motivated and really well funded, these units are generally too heavy and expensive for outdoor use. But there are some
indications that this may soon change.