Sunday, September 20, 2009

WMS and Bing/Yahoo Basemap Overlays

Here is an interesting issue I found today with WMS overlay. When WMS layers are created in either Mapserver or Geoserver then added as overlays to Yahoo or Bing their alignment is wrong.

Let me step back. As mentioned in earlier posts. One can create a WMS layer in geoserver and through the excellent config interface add this as a layer to Google earth.

All align perfectly. Now adding the same WMS to Modest Maps and overlaying it on Yahoo shows the WMS misaligned:

Turning to Openlayers, I find the same problem:

In each of the latter cases the WMS layer also looks stretched. I'll find the fix and post it.


Faridur R Choudhury said...

this usually happens because your WMS layers use SRS 4326 whereas the public map providers like Google, Yahoo and Bing uses SRS 900913. You'll need to add additional parameters to your WMS request string to reproject on-the-fly. Geoserver understands 900913 but Mapserver needs to be told by adding a line in the projection definition file. let me know if you need details on how to do it.

Faridur R Choudhury said...

've a look at my blog post "‘Bing’ oh! – ArcGIS, Flex, WMS and Bing" This might give you some pointers.

Matt Sheehan said...

Many thanks for you feedback. I'll take a look and follow up if it is still a problem.