On Sep 2, 2010, at 10:18 AM, ext Nigel Pickering wrote: > Hi > > I use OL with GeoServer and Apache web server (right now on localhost). I > want help clarifying my understanding of how projections work with OpenLayers: > > - If the layer projection is different from the map projection then > the layer will be automatically re-projected. Correct?
The map object projection is used as a default for all layers that don't specify their own projection. The base layer of the map will control the projection used to request images from WMS-based overlays (so changing the base layer changes the requests, which acts as reprojection). Many other overlay datasources (TMS, etc.) don't support reprojection, and OpenLayers can't do anything about htat. > - Without GeoServer the re-projection is done on the client side by > OL - vector layers but not images. Correct? OpenLayers has support to transform vector layers that are overlays to the projection of the map. > - With GeoServer the re-projection is done on the server side – both > vector and images (but images are slow). Correct? Not always true. You can configure vectors to be converted either on the server or the client depending on your settings. > > So if I want to offer both Google base layers (requires map projection of > 900913) and other base layers (not in 900913), then it can be done with > OL/GeoServer, but the re-projection of the non-Google images is slow. To > speed things up, would it possible to change the map projection on the fly to > match the new base layer? The re-projection of image layers in a WMS typically isn't that slow. (Slower than not doing so, but not usually that noticible, in my experience.) I don't understand the last question, however. If you are combining two sets of images in different projections, the server will need to transform one set. -- Chris > > Thanks, > > Nigel > > <ATT00001..txt> _______________________________________________ Users mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/openlayers-users
