On Aug 30, 2010, at 03:38 , Gabriel Roldan wrote: > But there's a thing I need to polish. For all this to actually work, we need > to ensure that the client's layer resolutions match the ones in GWC (and also > the tileOrigin?). > > So I'd appreciate some advise on how to ensure that to the extent possible. > How do the OL clients figure out the tile origin and resolutions when dealing > with the regular WMS? do them just use the CRS area of validity?
OpenLayers sets up the grid for each zoom level based on the maxExtent the layer is configured with, and the current resolution (which is a factor-of-2 subdivision of the maxResolution of the map's base layer). I think this does not work with GWC, because the resolutions come from a different layer than the extent. As David already pointed out, in GeoNode, we take the maxExtent for each layer from the WMS capabilities. And the tileOrigin vendor param is configured on the application level for the layer, as the lower left corner of this maxExtent. > Would it help if we enhance the GeoServer WMS GetCapabilities document to > supply the WMS-C VendorSpecificCapabilities if the GetCapabilities request > comes with TILED=true? We would not benefit from that, because the resolutions array is always determined by the map's base layer, not the layer itself. In my opinion, our best option would be to always configure the map with the validity extent of the CRS and a maxResolution that fits the maxExtent's width in the CRS map units to 256 pixels (or whatever resolution assumption is made - this is the one for EPSG:900913). All layers should request tiles that match this grid. The question is: how crucial is the tilesorigin vendor param to avoid duplicated labels? If the tilesorigin can also be the origin of the CRS validity extent, we wouldn't even have to parse GetCapabilities for WMS at all. -Andreas. > > > Desperately looking for your help :) > Gabriel. > > Gabriel Roldan > [email protected] > Expert service straight from the developers > -- Andreas Hocevar OpenGeo - http://opengeo.org/ Expert service straight from the developers.
