[OSM-talk] Invisible waypoints

Andrew Findlay andrew at findlay.org
Sun Mar 26 00:07:54 GMT 2006


On Sat, Mar 25, 2006 at 08:42:23PM +0000, nick at hogweed.org wrote:

> > 1)	I had to edit MainWindow2.cpp to set the name of my serial
> > 	device. This needs to be read from a config file and/or set in
> > 	the GUI.
> 
> True --- again one of those little things I've been meaning to do but never 
> got round to. Will do for the new version.

Great, thanks.

> > 2)	Having read in a lot of tracks from the GPS, the window was
> > 	blank because it had chosen an origin and zoom that did not
> > 	include any data points. This was probably made worse by the
> > 	fact that the data includes tracks from both the UK and New
> > 	Zealand! Interestingly, it was not very far off the NZ tracks
> > 	and I was able to scroll across to a known point.
> 
> It sets the location to the average of all nodes read in from the .osm file, 
> so I'm guessing you have more New Zealand data than UK.

Lots more. The UK data was not really supposed to be there, but as I
was in the UK when I downloaded it the GPS was recording a UK location
at the time! A geometric mean or an arithmetic median might be a
better choice, with the scale set to include a reasonable proportion
of the data points on-screen.

> > 3)	When I saved the data in .osm format and read it in again, the
> > 	track points were grouped in vertical lines. It looks as if
> > 	the save process limits the number of *significant figures*
> > 	rather than the number of *decimal places* on lat/long data.
> > 	Thus, for places in NZ we get lines like:
> >
> > 	<node lat='-36.1602' lon='175.355' uid='-12' tags='class=trackpoint;'/>
> >
> I've never noticed this precision giving me a problem. However I have (just 
> now) altered it in the code - the reason why it was 6 significant figures was 
> that that is the default value for the QTextStream (Qt output stream). I've 
> changed it to 10.

Good. This would not be a problem for UK data as the Lat is around 53
(two digits) and Long very close to zero (one digit at most). By
comparison, in NZ the Longitude is always three digits (approx -175)
which does not leave enough after the decimal point to match the
precision of the GPS receiver.

Andrew
-- 
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