[OSM-dev] Slippy map tiles mismatch

Jon Burgess jburgess777 at googlemail.com
Tue Feb 23 23:29:16 GMT 2010


On Tue, 2010-02-23 at 16:46 -0500, Matt Hampel wrote:
> On Tue, Feb 23, 2010 at 2:18 PM, Jon Burgess <jburgess777 at googlemail.com> wrote:
> > On Tue, 2010-02-23 at 11:31 -0500, Matt Hampel wrote:
> >> That's certainly possible, but I'm still not sure how to get closer to
> >> a solution for pre-rendered tiles. To render the tiles, I'm following
> >> steps at
> >> http://wiki.openstreetmap.org/wiki/Slippy_Map and
> >> http://wiki.openstreetmap.org/wiki/Mapnik#Rendering_tiles
> >> using a shapefile extract instead of the full OSM export in PostGIS
> >
> > It should not make any difference whether you go down the pre-render
> > route or not.
> >
> > What projection do you have in the <Map> element of your style?
> >
> > What does the definition of the shapefile datasource look like?
> >
> 
> I have tried using two shapefiles (one reprojected into NAD83) and two
> corresponding projections in the Map element.
> 
> NAD83:
> <Map srs="+proj=latlong +ellps=NAD83 +datum=NAD83 +no_defs">

The default osm.xml map style uses the google-style 900913 projection.
If you want to generate a latlong map then you will also have to update
the projection string in generate_tiles.py. Have you done this?


> Layer SRS WKT:
> GEOGCS["GCS_North_American_1983",
>     DATUM["North_American_Datum_1983",
>         SPHEROID["GRS_1980",6378137.0,298.257222101]],
>     PRIMEM["Greenwich",0.0],
>     UNIT["Degree",0.0174532925199433]]
> 

That should be OK, but I wanted to see the <Datasource> block in your
style for this shapefile. There are some easy mistakes which can be made
in setting up the layer projection and extent.

	Jon







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