[OSM-talk] gdalwarp question

Jukka Rahkonen jukka.rahkonen at mmmtike.fi
Sun May 3 13:11:06 BST 2009


Torsten Mohr <tmohr <at> s.netic.de> writes:

> 
> Hello,
> 
> thanks for that hint.
> 
> Right, the chosen projection won't work around the poles, i don't expect
> that.  In the call to gdalwarp i gave the source projection (EPSG:4326 or
> WGS84) and as target projection i gave the projection used in osm.xml.
> 

Hi,

Your target projection is the so called Google projection, or epsg:900913, or
nowadays officially epsg:3785.  It is the projection used in OSM slippy map, but
the native OSM data are in epsg:4326.  Therefore you should warp the downloaded
images _into_ epsg:4326, not from that.  Unfortunately I cannot say what would
be the correct source projection definition for your original images.

An easy way to test your warped images is to download some OSM data in shapefile
format and in epsg:4326 projection from Geofabrik.de, open the warped image with
some GIS program like QGis or OpenJUMP together with OSM shapefile and see if
they suit well together.  

Gdalwarp options are documented at http://gdal.org/gdalwarp.html but some
further reading may be necesssary to understand what all the options mean.

-Jukka Rahkonen-






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