[Openstreetmap] london free maps...

[Matt Amos]

On Friday 12 November 2004 18:44, Petter Reinholdtsen wrote:
> [Matt Amos]
> > determining how to convert raw GPS tracks into something more
> > useful is something i've been giving a lot of thought to,
> > recently. unfortunately, i haven't managed to think of anything
> > beyond the obvious, so far. its a Difficult Problem ;-)
>
> One idea I had from image processing is to use the Hough transform
> to locate lines in the set of points.  A quick search on Google
> gave me these references:

Hough transforms are a good idea, especially if you take into account 
the DOP-sphere of the GPS point.

however, my concern is that they wouldnt pick up on routes which are 
highly non-straight, such as twisty country/mountain roads, etc...

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?

> I do not have that much yet, because I do not want to collect lots
> of points if the information collected is lacking accuracy info.

i know what you mean, but i think lots of innacurate info is probably 
as good as lots of accurate info. its just that little accurate info 
is much better than little innaccurate info.

> Converting my database to GPX should be fairly easy, so I'll try to
> hack something together in the near future.  Is there a good
> reference explaining GPX?  The doc available from
> <URL:http://www.topografix.com/GPX/1/1/> isn't too good.

i only found out about this really on saturday night, but it seems 
like the Right Tool for the Job. i had already put down some notes on 
"a nice format for tracks" and it looked eerily similar ;-)

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.

what i'm proposing is that we extend GPSX to have optional fields for 
these and (maybe) give it a full XML DTD, then contribute it back to 
GPSX so that it is "standard" in some way. disclaimer: i have done 
very little work with XML before and might be proposing something 
very difficult.

cya,

matt
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