[ gpsdrive ] Mapnik Projection used by gpsdrive

[Jan-Benedict Glaw]

On Tue, 2008-09-23 14:46:32 +0200, Guenther Meyer <d.s.e at sordidmusic.com> wrote:
> Am Dienstag 23 September 2008 schrieb Jan-Benedict Glaw:
> > On Mon, 2008-09-22 15:37:01 +0200, Guenther Meyer <d.s.e at sordidmusic.com> 
> wrote:
> > osm2pgsql was changed. The "old" version wrote something that's
> > compatible with the "short" projection string, while up-to-date
> > versions (eg. *not* those of the osm2pgsql Debian package....) write
> > something that's compatible with the "long" string. The newer
> > osm2pgsql versions can also behave like the old versions, if the "-M"
> > command line option is used.
> >
> > But since OSM switched, I think the best way for gpsdrive would be to
> > also use the "new" scheme and to force users to update their
> > databases, caches and osm2pgsql. The benefit would be that they only
> > need one database for general OSM/Mapnik use and gpsdrive, instead of
> > two. (Or fiddle with projection parameters.)
>
> that's right.
> but it's not a good solution to use a fixed projection. who knows how often 
> they will change it?

Nobody, unfortunately.

> so the best way is to read the projection from the database, if possible, or 
> to store it somewhere on database creation.

A quick look at the osm2pgsql code tells me that this isn't stored
anywhere, but I may be wrong. Though, it probably would be nice to add
another table with at least the used SRS, or even the whole projection
string.

> > As a side note: If you use (or want to follow) the *current* osm.xml
> > from OSM SVN, you'll loose the amenity layer (eg. parking places,
> > recycling boxes, ...) because the current osm2pgsql's default.style
> > converts an additional column, which is missing from the old version
> > and required by up-to-date osm.xml files (from SVN).
> additional column? which one? so osm2pgsql won't create the amenity column 
> anymore?

`power_source' was added. It's referenced in the filter rule for
electric generators based on wind mills. But this seems to break
generation of the whole Mapnik layer.

> > Unfortunately, 
> > Mapnik fails quietly if a filter references a non-existing column and
> > doesn't draw the whole layer.
>
> that's bad.
> I mean, we don't need mapnik to draw those data, because gpsdrive has its own 
> layer for that. but failing and drawing nothing is really bad...

I'd like to get some box to test Mapnik SVN vs. released 0.5.1 version
(as of Debian's packages). Maybe that bug is even fixed, but I *try*
to only install software with Debian packages.

If anybody of you has Mapnik SVN installed, please modify one filter
rule (in osm.xml) to reference a non-existing tag name (each tag name
is converted to a SQL column.)  If the layer fails to draw, current
SVN Mapnik is still buggy. (I suggest modify one of the amenity rules
and s/amenity/amenity_not_in_database/ and just try to find a Parking
symbol :)

MfG, JBG

-- 
      Jan-Benedict Glaw      jbglaw at lug-owl.de              +49-172-7608481
Signature of: 17:45 <@Eimann> Hrm, das E90 hat keinen Lebenszeit Call-Time Counter mehr
the second  : 17:46 <@jbglaw> Eimann: Wofür braucht man das?
              17:46 <@jbglaw> Eimann: Für mich ist an 'nem Handy wichtig, daß ich mein
                              Gegeüber hören kann. Und daß mein Gegenüber mich versteht...
              17:47 <@KrisK> jbglaw: was du meinst ist wodka.
              17:47 <@KrisK> jbglaw: es klingelt und man hört stimmen
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