[Openstreetmap] GPS point submission format

Matt Amos matt at matt-amos.uklinux.net
Mon Nov 15 00:09:56 GMT 2004


On Saturday 13 November 2004 12:56, SteveC wrote:
> * Petter Reinholdtsen (pere at hungry.com) wrote:
> > Unrelated to this, it would be useful if the format used would
> > include the raw satellite information, with enough information to
> > make it possible to post-process the GPS data using differential
> > GPS data to increase the accuracy of the measurements.  Check out
> > <URL:http://www.wsrcc.com/wolfgang/gps/dgps-ip.html> for more
> > info on this.  It would be able to remove most of the error
> > introduced by the selective availability, and might even be able
> > to reduce the error introduced by the disturbances from the
> > atmosphere as well.
>
> Matt has been thinking/doing things in this direction, maybe he can
> fill us in?

for certain chipsets you can pull pseudo range and availability info 
out of the GPS unit (i have a SiRF-based and it works with SiRF 
binary protocol, but i hear it works with Garmin's protocol as well).

this allows you to post-process later, assuming the availability of 
fixed listening stations "near" you. (where "near" means they see the 
same satellites - they can be up to 300 miles away, iirc).

there are models available online under the GPSToolkit aegis which can 
do sophisticated offline DGPS and atmospheric modelling. this can 
bring your position down to within 2m, alledgely. personally, i 
havent finished writing the SiRF drivers yet, so i couldnt say.

also the system is gonna have problems in a multi-bounce environment, 
since that is an additional (sometimes very large) source of error 
which cannot be subtracted out.

cya,

matt
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