[ gpsdrive ] Mapnik maps offset by a few meters

[Enigma]

On Thu, Apr 30, 2009 at 5:00 AM, Hamish <hamish_b at yahoo.com> wrote:

>
> Enigma wrote:
> > I recently upgraded the OS on my GPS
> > computer and I am seeing a problem with mapnik maps.  No
> > matter how I load the data in osm2pgsql the maps in GPSDrive
> > are off by about 10 meters to the north and 10 meters to the
> > west.  My GPS position, as well as tracks, POIs, waypoints,
> > etc. are all displaced on the map by a few meters.  I am
> > using the latest SVN for GPSDrive, mapnik 0.6.0 and the OSM
> > tools are from SVN.  I have seen the issue where the no
> > projection was used causing positions to be off by many
> > kilometers, but this off by a few meters issue is a new one
> > for me.  Has osm2pgsql changed the projection they use like
> > described here:
> http://lists.gpsdrivers.org/pipermail/gpsdrive/2008-September/001420.html
> > ?
>
> to be technical, I think that is a matter of datum transform rather than
> map projection.


I'm no cartographer - I'll take your word on that.


>
>
> > Do I need to use an older version of mapnik or osm2pgsql
> > to be compatible with GPSDrive?  I am seeing this issue on
> > 2 different computers so I don't think it is unique, is
> > anyone else seeing anything like this?
>
> I don't know if it applies to Mapnik support, but see this bug report:
>
> http://sourceforge.net/tracker/?func=detail&aid=2203405&group_id=148048&atid=770280
>
> what map scale?
> is it a constant 10m to N+W all over the map for all maps?
>

It looks to be constant.  I first noticed it at close scales but if I zoom
out the offset is still there.  It doesn't look like it gets bigger with the
wider scales - it stays at about 10m offset.  I'm fairly sure that it is not
in the actual data because I was using the same extracts for my old
installation that was displaying correctly.  I am loading some data for a
slightly lower latitude right now to see if the behavior changes at all.

Josh



>
>
> Hamish
>
>
>
>
>
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