[OSM-talk] find corners of exported maps

Dirk-Lüder Kreie osm-list at deelkar.net
Thu Dec 4 15:55:56 GMT 2008


Olav Kvittem schrieb:
> Hi,
> 
> I wonder how I compute the coordinates of the corners of the images 
> received from the web export function
> for an osmarender image. I specify geodetic center position(degrees), 
> zoom level and image size and get at nice map image.
> The projection is of cource Mercator and I can linearly map mercator 
> coordinates onto the image.
> But how do I know the coordinates of the corners of the returned image ?
> 
> The url I use is :
> http://server.tah.openstreetmap.org/MapOf/index.php?long=10.17456&lat=56.01566&z=6&w=500&h=592&format=png' 
> 
> 
> The tile-size for each level is 256x256 so given the zoom-level I could 
> compute the pixel density from the
> world map size in mercator projection.
> That works for east direction which is linear, but for the northern 
> direction the projection is nonlinear and
> I am not sure if the geodetic center that I specify is at the center of 
> the returned image or not.

have a look at the debugHelper.pl in tiles at home. it will give you the
latlon center of the tile bbox and the latlon of the center of the tile.



-- 

Dirk-Lüder "Deelkar" Kreie
Bremen - 53.0952°N 8.8652°E

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