[ntp:questions] Re: First Galileo satellite launched

Terje Mathisen terje.mathisen at hda.hydro.com
Thu Dec 29 06:58:41 UTC 2005


David L. Mills wrote:

> Danny & Co.,
> 
> I'm not a defender of any political agenda here, but I would like to
> correct the general assumption, as evident in the interviews last night,
> that the Galileo system is more accurate than the GPS system. The GPS L1
> signal available to the general public has a nominal accuracy (PDoP) of
> 30 meters; however, with the L2 signal and P code with capable receiver,

The current reality of GPS+WAAS/EGNOS is _much_ better:

I have documented that with good antenna placement (360-degree
visibility, small ground plane, no multipath), it was possible to
monitor a single position in southern Norway over a two-week period last
summer, with 67% of all measurements within about 1 m, 90% within 2 m,
and 95% within 2.7 m.

Excepting a single 30-second outlier period (with position errors up to
30 m), the worst offset I measured during this period was just over 3 m.

> it has a nominal PDoP of one meter, comparable to Galileo. The P code is
> available only to the USA military at present. I would assume once
> Galileo reaches operational status there is no need to keep the P code
> secret.
> 
> Folks might forget the Russian GLONASS system, which is very similar to
> GPS and Galileo, has been around for over twenty years. It is not clear
> how long it will last or whether it can be maintained to the order of
> GPS and Galileo.

As I mentioned in my previous message, Ashtech makes combined
GPS+Glonass receivers, they received a series of patents for this back
in 1999:

http://products.thalesnavigation.com/en/news/releases/viewRelease.asp?id=130

Terje

-- 
- <Terje.Mathisen at hda.hydro.com>
"almost all programming can be viewed as an exercise in caching"




More information about the questions mailing list