WMS: bbox berechnen

Hallo,

ich frage mich, warum diese beiden WMS-Server (bei 26° Azimut der bbox Koordinaten) unterschiedliche Tiles liefern:

DTK10 ca. 26° Azimut (Tiles ueberlappen):
http://www.geoserver.nrw.de/GeoOgcWms1.3/servlet/DTK10?SERVICE=WMS&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&LAYERS=Raster:DTK10:Dtk10G&SRS=EPSG:4326&STYLES=,&FORMAT=image/png&TRANSPARENT=TRUE&WIDTH=500&HEIGHT=500&BBOX=6.72913,51.5836,6.73462,51.5863
http://www.geoserver.nrw.de/GeoOgcWms1.3/servlet/DTK10?SERVICE=WMS&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&LAYERS=Raster:DTK10:Dtk10G&SRS=EPSG:4326&STYLES=,&FORMAT=image/png&TRANSPARENT=TRUE&WIDTH=500&HEIGHT=500&BBOX=6.72913,51.5808,6.73462,51.5836

DTK10 45° Azimut (Tiles passen aneinander):
http://www.geoserver.nrw.de/GeoOgcWms1.3/servlet/DTK10?SERVICE=WMS&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&LAYERS=Raster:DTK10:Dtk10G&SRS=EPSG:4326&STYLES=,&FORMAT=image/png&TRANSPARENT=TRUE&WIDTH=500&HEIGHT=500&BBOX=6.72913,51.58360000,6.73462000,51.58909168
http://www.geoserver.nrw.de/GeoOgcWms1.3/servlet/DTK10?SERVICE=WMS&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&LAYERS=Raster:DTK10:Dtk10G&SRS=EPSG:4326&STYLES=,&FORMAT=image/png&TRANSPARENT=TRUE&WIDTH=500&HEIGHT=500&BBOX=6.72913,51.57810845,6.73462000,51.58360000

DGK5 ca. 26° Azimut (Tiles passen aneinander):
http://www.wms.nrw.de/geobasis/adv_dgk5?REQUEST=GetMap&VERSION=1.1.1&SRS=EPSG:4326&LAYERS=Grundriss%2CHoehen&STYLES=&FORMAT=image/png&WIDTH=500&HEIGHT=500&BBOX=6.72913,51.5836,6.73462,51.5863
http://www.wms.nrw.de/geobasis/adv_dgk5?REQUEST=GetMap&VERSION=1.1.1&SRS=EPSG:4326&LAYERS=Grundriss%2CHoehen&STYLES=&FORMAT=image/png&WIDTH=500&HEIGHT=500&BBOX=6.72913,51.5808,6.73462,51.5836

DGK5 45° Azimut (Tiles passen aneinander):
http://www.wms.nrw.de/geobasis/adv_dgk5?REQUEST=GetMap&VERSION=1.1.1&SRS=EPSG:4326&LAYERS=Grundriss%2CHoehen&STYLES=&FORMAT=image/png&WIDTH=500&HEIGHT=500&BBOX=6.72913,51.58360000,6.73462000,51.58909168
http://www.wms.nrw.de/geobasis/adv_dgk5?REQUEST=GetMap&VERSION=1.1.1&SRS=EPSG:4326&LAYERS=Grundriss%2CHoehen&STYLES=&FORMAT=image/png&WIDTH=500&HEIGHT=500&BBOX=6.72913,51.57810845,6.73462000,51.58360000

Vielen Dank, Dirk