I have some problems with my WMS layer (UTMZ32N, EPSG:25832) hosted using
either GeoServer 2.1.4 or 2.2b2. When I overlay my WMS layer with a tile from
the same dataset, there is a slight offset between them (0-2pixels I estimate).
The direction of the offset seems to vary - probably depending on the extent
(see image 1 from QGIS).
I visualized the same area in OpenJump and inserted a couple of points in a
separate vector layer (for georeference) seen in image 2. The pixel border
should be going through the two left most visible crosses but they aren't.
I created a direct request to GeoServer base on image 2 and the displayed
coordinates from OpenJump (captured by hovering over the corners if the map -
which at least gives me millimeter accuracy):
http://myserver:8080/geoserver/ows?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&BBOX=530999.95,6154999.8404,531000.1592,6155000.0001&CRS=EPSG:25832&WIDTH=619&HEIGHT=473&LAYERS=niras:ddo2010_rgb&STYLES=&FORMAT=image/jpeg
The result from the request in seen in image 3, where the pixel intersection
clearly is off especially on the northing axis (since top is 6155000.0001 and
the intersection should be at 6155000.0000).
Why is there an offset and where does it come from?
Is it because I expect too much from GeoServer with regards to accuracy and
machine accuracy (rounding errors)? Though I don't know if it explains the
0-2pixels offset I experience on a normal zoom level.
Regards from Casper
[1] - http://i49.tinypic.com/2ikv53o.jpg
[2] - http://i50.tinypic.com/2eatbvo.jpg
[3] - http://i46.tinypic.com/fubcx3.jpg
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