[OpenLayers-Dev] WMS request mod

Dominik Mikiewicz dominikmikiewicz at o2.pl
Fri May 20 03:33:26 EDT 2011

Yeah, I should have added - large scales are fine (> 1m, 500k), small are

-----Original Message-----
From: andreas.hocevar at gmail.com [mailto:andreas.hocevar at gmail.com] On Behalf
Of Andreas Hocevar
Sent: Friday, May 20, 2011 9:26 AM
To: Dominik Mikiewicz
Cc: Ray Di Ciaccio; openlayers-dev at lists.osgeo.org
Subject: Re: [OpenLayers-Dev] WMS request mod

This approach will only work well for tiles that are near the equator,
or don't span over a wide range of latitudes. It is basically the same
thing that happens when you use the not recommended reproject: true
option for Layer.WMS.


On Fri, May 20, 2011 at 8:54 AM, Dominik Mikiewicz
<dominikmikiewicz at o2.pl> wrote:
> This should work just fine. There won't be a serious performance hit
either as you only recalculate bbox and change srs on the clientside. I do
it quite often and even extended a wms layer class so I can quickly set up
my 4326 layers to work with spherical Mercator.
> However you may experience some issues with tile caching as sometimes the
precision may vary from browser to browser. Another thing is the
getFeatureInfo request - make sure you send correct cords if you are going
to use it.
> dom
> -----Original Message-----
> From: openlayers-dev-bounces at lists.osgeo.org
[mailto:openlayers-dev-bounces at lists.osgeo.org] On Behalf Of Ray Di Ciaccio
> Sent: Thursday, May 19, 2011 6:00 PM
> To: openlayers-dev at lists.osgeo.org
> Subject: [OpenLayers-Dev] WMS request mod
> Sorry for the previous messed up message. Let me try this again:
> Hi all,
> I'm in what I'm guessing is a fairly common situation -- I'm using
> Google Maps as my baselayer (so map is in EPSG:9009l3 projection) and
> I'm trying to load an overlay from a WMS which I have no control over.
> It only offers data in EPSG:4326. The WMS request generated by
> OpenLayers will be for CRS=EPSG:900913 and the BBOX values will be in
> EPSG:900913. This obviously won't work if the WMS only offers EPSG:4326.
> My solution to this problem was to override
> OpenLayers.Layer.WMS.getFullRequestString() so that it uses the
> projection that I set for that particular layer -- it changes the
> CRS/SRS param to whatever the layer projection is, and it transforms the
> BBOX values from the map projection to the layer's projection. This way
> I get a valid request for the WMS and it's loaded in the correct
> location on the basemap. My question is whether this is the right
> approach to this situation and whether there may be unforeseen
> repercussions to these changes I made.
> Thanks!
> - Ray
> --
> Ray Di Ciaccio
> MIT LL, Group 42
> 781-981-2024
> ray.diciaccio at ll.mit.edu
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Andreas Hocevar
OpenGeo - http://opengeo.org/
Expert service straight from the developers.

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