[2011 September] UPDATE : new Openlayers 2.11 works quite well on iPad/iPhone.
I have experimented with OpenLayers 2.9 using touch.js extension for capturing touch events from iPhone/iPad. Although stripped down version of OL is about 184KB, the performance is very bad. If you have iPhone/iPad check this experiment: http://www.sumbera.com/lab/iphone/katastr.htm (note it will not work from desktop browser)
Meanwhile I have tested new GoogleMaps v3 how it works on iPhone/iPad. despite few problems (stability, problems with cached tiles or disconnected JavaScirpt to load new tiles -iPad) it works pretty well . Check yourself this page from your mobile touch device (iPhone.iPad,Android): http://www.ikatastr.cz/iKatastrM.htm
Conclusion : Google Maps v3 wins on mobile over the Openlayers 2.9
Is it possible to display WMS (EPSG:4326) over the Google (EPSG:900913) in Openlayers ? Yes ! thanks to the great img ‘feature’ that enables you to shrink/expand your return image based on defined image size. That means that if your map view is rectangular or you request WMS as tiles (rectangular too) you get proper overlay of EPSG:4326 on EPSG:900913) . Example of various image sizes follows (these are actually WMS GetMap requests):
Here is the way how to implement it in OpenLayers – very simplified:
Playing with OL context and OLON (OpenLayers Object Notation) that is based on JSON I have found that the sample provided on the OLON sandbox in OL repository doesn’t work well with vectors, in fact it ignores vectors at all. Reading through the code it was quite easy to discover the problem – vector.js (layer) didn’t serialize “features”, moreover during deserialization, features were nulled. To make OLON properly work in OL 2.7 for vectors, add following to the vector.js (lib\OpenLayers\Layer\Vector.js)
I have put together preview for visually shaking maps where you don’t get just map layer names, but also preview of layers ! Somehow I couldn’t find any page on internet that would allow you to display layers from GetCapabilities WMS as image thumbnails. I’ve kept this idea for a long time and actually it started with yahoo pipes year ago – why not to visually display GetCapabilities as RSS feed with image thumbnails referenced as media type in the feed ? after little experimenting I realized that the value is in combination of position and WMS information, so the use case is “I am here on this place and hey WMS servers, give me all you know about this place…”