Digital Finds

joseph dot reeves at thehumanjourney dot net

Improved GPS coverage across Europe

Oct 05, 2009 by Joseph Reeves

Loads of exciting things happened on October 1st; one of the things that interested me the most was that the EGNOS system went operational. By using geostationary satellites and ground base stations, the EGNOS system presents a GPS "overlay" to the user that enables a horizontal accuracy of somewhere between 1 and 2 meters.

It seems that the base stations on the ground receive conventional GPS signals, work out the relevant error rates and distribute these to users via the geostationary satellites. The system has been up and running for some time, in test mode, and compatible receivers have been sold, I'm told; the important thing about the first of October, however, was that the system is now live and available to all as a free and open service. It's "operational".

There's a press release and some more details. I'm particularly interested in SISNeT; a system that sends the EGNOS data via the internet rather than the new satellites; a free D-GPS system somewhat like the aGPS software that I packaged up for Openmoko. The benefits of SISNeT should come in situations where a clear view of the sky can't be guaranteed - busy urban centres and the like (whereas EGNOS was developed with a strong bias towards aviation; pilots always have a decent view of the horizon).

I'm guessing that my Openmoko will make good use of this service long before my (otherwise very nice as a GPS, but rubbish when it comes to new software) Nokia N96 does...


How would you go about actually using the SISNeT data on the handset?

Consumer grade GPS receivers don't provide raw pseudoranges (with standard firmware) so the positioning solution can't be calculated on the handset.

The only other approach I can think of is to convert the SISNeT data to RTCM and feed that into the receiver. AFAICT the conversion is certainly possible but non-trivial. Are you aware of any software solution that would take care of that step?



PS: The ublox chip in the FreeRunner supports EGNOS but probably has that feature disabled (The chips come with this configuration from the factory due to reliability issues during the EGNOS test phase). It might be worth rolling out a software upgrade to users that enables EGNOS, e.g. on power up.

Posted by Rene Wagner on October 06, 2009 at 07:15 PM BST #

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