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. cheers Olav perl code for computing the pixel density # $ol = east length of map section # pix,$piy = pixel size of image # find zoom level my $dnmax=85.0511; # max for osmarender my ($momax, $mnmax)=mercate($dnmax, 180); my $zlevel=int( log( 2*$momax / $ol ) / log(2) + 1); # osm zoom # find real size of map my $ompp=2*$momax/(2**$zlevel)/256; # east meters per pixel for this level my $nmpp=2*$mnmax/(2**$zlevel)/256; # north meters per pixel for this level _______________________________________________ talk mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk
