The Data that Threatened to Break Physics

[Urwumpe]

Thanks for that. How is the proposed centimeter accuracy GPS supposed to work?

Bob Clark

You mean WAAS? That's already reality. It emits correction data for the whole service area and all GPS satellites, like Ionosphere data and clock drift parameters. It also tells the receiver which satellites are more accurate than others and which it should prefer in the weighted sum calculations for the position.

It already allows 90 centimetre accuracy, if your receiver is capable of it. LAAS should further improve this for aircraft, but that's still in the outer rings of development hell.

Additionally there are DGPS reference stations all over the more developed countries, that are used by geographers with higher accuracy, it results in 22 cm error for every 100 km distance from a reference station. With more sophisticated methods, geologists even measure mm movement of volcanoes.

 

[kamaz]

Also, position fix error follows a normal distribution, so if the receiver does not move, you can in principle get infinite accuracy by averaging enough measurements. Cannot be really done with time, because you would need a reference clock more precise than the one on the satellite, and this would be... expensive.

Differential GPS (DGPS) operates by having a fixed master receiver at known position (which can be determined very accurately using astronomical methods for example). Let's sat that the true position of the receiver is X,Y. The GPS fix of the master is going to be X+x(t), Y+y(t). The x(t),y(t) error vector is transmitted to the slave receiver which substracts it from its own GPS fix, thus obtaining the true position. Of course this assumes that positioning error at the salve site is the same as at the master site, and this is not true, so the accuracy drops as the master-slave distance increases.

WAAS is conceptually the same thing, except that the fixes are distributed via satellite, so this is less accurate... Still gives you 0.9m CEP which is enough for most applications.

 

[garyw]

Exactly. From now on, being the good scientist by reporting an experimental problem is likely to get you fired, if your experiment is unlucky enough to attract press interest.

I heard an interview of someone outside that group, perhaps a month or two later, and he was very critical and stating they simply should not have published the original paper - but it seems they were compelled to.

add that outrage to this http://www.dailymail.co.uk/news/art...rthquake-Italy-killed-309-people-cleared.html and it'll put people off of science which is last thing that should be allowed.
The world is going crazy.

 

[Andy44]

add that outrage to this http://www.dailymail.co.uk/news/art...rthquake-Italy-killed-309-people-cleared.html and it'll put people off of science which is last thing that should be allowed.
The world is going crazy.

Yeah, that was the first thing I thought of, too.

It's almost like reverse witchcraft trials, you condemn them for not practicing the Dark Art!