[Openstreetmap] london free maps...

Matt Amos matt at matt-amos.uklinux.net
Tue Nov 16 20:24:42 GMT 2004

On Monday 15 November 2004 00:34, Petter Reinholdtsen wrote:
> [Matt Amos]
> > any set of algorithms we put together is going to have
> > difficiencies, so i think it might be good to have Hough as stage
> > 1 out of N of the automatic processes?
> Yes.  It might work fairly well for cities. :)

on the assumption that streets in cities are generally straight. it'd 
work better in the States than in the UK, i think ;-)

> > from what i've heard GPSX doesn't allow for extra fields, such as
> > DOP, PR, ephemeris to be included and i really think that we want
> > these fields, if at all possible, to increase our accuracy.
> It includes dilution of precision and a number of other fields. 
> Look for hdop and vdop.  I have no idea what you mean with PR and
> ephemeris, so I suspect those are missing from GPX.

having actually read the format in detail i can say: it does support 
PR and ephemeris, in the extensions field. PR (pseudo-range) is a 
measure of time for signals to reach you from each satellite. its the 
raw data from which the GPS unit calculates your position. ephemeris 
is positional data about the orbits of the satellites.


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