[OSM-newbies] Detect WAAS/EGNOS mode

[Lauri Hahne]

Even though there is a limited amount of stations, there are plenty of
satellites sending signals from all directions and, on the other hand,
ionospheric weather isn't fragmented but correlates heavily locally, so the
estimates provided by SBAS are much better than having no estimate. The
system even works so great that it's currently being certified for safety
critical applications which effectively renders all "SBAS is shit" arguments
worthless.

2008/4/25 ael <law_ence.dev at ntlworld.com>:

> Lauri Hahne wrote:
> > SBAS satellites generally transmit correct parameters for satellite
> clock,
> > ephemeris and ionospheric errors. Of these the ionospheric errors are the
> > biggest error source in regular GPS system. Ionospheric corrections are
> > transmitted as a map, not as single variables. The receiver locates it in
> > this map/grid and uses the local correction values.
> >
> > The correction grid is generated from information provided by the
> > landstations. This method is similar to constructing a weather map and
> thus
> > the corrections you are using are always "local". If you're out of the
> > broadcast range, then your receiver won't do any corrections at all. Thus
> > all your assumptions that you're getting bad correction if you're too far
> > off is completely bs. The data transmitted by SBAS signals also makes it
> > possible to calculate accurate approximations for positioning error. Eg
> > EGNOS promises that using their signal, you can get about 1 metre
> accuracy
> > across Europe.
>
> Thanks for the informed posting. But given that the base stations can
> only sample small (integrated) portions of the ionsphere, the correction
> grid must still be subject to errors, just like a weather map.
> Presumably that 1 metre accuracy must be at some confidence level
> reflecting the sampling and typical length and time variations in the
> ionsphere.
>
> ael
>
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-- 
Lauri Hahne
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