Increasing GPS accuracy with EGNOS

Al Johnson openmoko at mazikeen.demon.co.uk
Thu Oct 22 10:24:05 CEST 2009


On Wednesday 21 October 2009, Ed Kapitein wrote:
> Baruch Even wrote:
> >> ><SNIP><
> >>
> >> I found this in the source of ogpsd on my Freerunner:
> >>
> >> def initializeDevice( self ):
> >>
> >>     # Use high sensitivity mode
> >>
> >>     #self.send("CFG-RXM", 2, {"gps_mode" : 2, "lp_mode" : 0})
> >>
> >>     # Enable use of SBAS (even in testmode)
> >>
> >>     self.send("CFG-SBAS", 8, {"mode" : 1, "usage" : 7, "maxsbas" : 3,
> >> "scanmode" : 0})
> >>
> >> So it seems that SBAS has always been enabled even in test mode. Does
> >> anybody know where we can get information if sbas is really active and
> >> used by the chip?
> >
> > The comment is wrong, the mode value of 1 means that it uses SBAS but
> > not if its in test mode. The comment is a left over from the time the
> > value was 3, but then the whole line was commented out.
> >
> >
> > You can get SBAS status messages if you set it in the debug interface
> > with: mdbus -s org.freesmartphone.ogpsd /org/freedesktop/Gypsy
> > org.freesmartphone.GPS.UBX.SetDebugFilter NAV-SBAS True
> >
> > and then listen to the signals with:
> > mdbus -l -s rg.freesmartphone.ogpsd /org/freedesktop/Gypsy
> >
> > Look for DebugPacket signals.
> >
> > I tried it for other signals, didn't have time yet to test if it works
> > for NAV-SBAS.
> >
> > Baruch
> 
> I did to enable the debug packet and although i was receiving data from
> PRN120, i never got any
> NAV-SBAS packets in the debug output.
> 
> Acording to [1] it should be enabled in the framework, so i am wondering if
>  anyone had more luck than me.

I found the same as you, but probably forgot to report it. I believe the 
reason is that by default the NAV-SBAS messages aren't enabled, and we don't 
explicitly enable them in configuration. I didn't get round to checking the 
message format required to enable it though.



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