[OpenLayers-Users] Tiles outside maxExtent being loaded

[Jon Blower]

Hi all,

I've noticed that in my application OpenLayers is requesting tiles
outside the maximum extent of my overlay layer (which is in EPSG:4326
and hence has a maxExtent of -180,-90,180,90).  I've checked using the
Firebug console that the maxExtent is correctly set.  wrapDateLine is
set true.

My map div has dimensions 512px x 400px (width x height).  When zoomed
such that the whole world is visible, I expect 2 tiles to be loaded
(with size 256x256), one for each of the western and eastern
hemispheres.  Instead, OL loads 8 tiles: the two "correct" tiles and
six other tiles - four above and two below the map.  I.e. it is
loading tiles with impossible latitudes.

The incorrect tiles have bounding boxes:
-180,90,0,270 (tile "above" western hemisphere)
0,90,180,270 (above E hem)
-180,-270,0,-90 (below W hem)
0,-270,180,-90 (below E hem)
-180,270,180,450 (two tiles above W hem)
0,270,180,450 (two tiles above E hem)

Is there any way of preventing these tiles from being loaded?  You can
see this effect at http://www.reading.ac.uk/godiva2 (load the web
page, then select an item from the LH menu to create an overlay).

Cheers, Jon


-- 
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Dr Jon Blower Tel: +44 118 378 5213 (direct line)
Technical Director Tel: +44 118 378 8741 (ESSC)
Reading e-Science Centre Fax: +44 118 378 6413
ESSC Email: jdb at mail.nerc-essc.ac.uk
University of Reading
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Reading RG6 6AL, UK
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