On Sat, Jan 19, 2008 at 01:16:15PM +0100, Andrea Maschio wrote: > > Il giorno 18/gen/08, alle ore 13:02, Christopher Schmidt ha scritto: > > > >The "X" in AJAX is for XML/XMLHttpRequest. XMLHttpRequest is not > >neccesary to receive tiles -- instead, the proper URL is simply stuck > >into an <img> tag, which (of course) can be loaded from other sites. > > Ok, so as I understand except fo wfs-t (that means transactional web > feature service and it's supposed to edit geometries and for this to > interact with the server) all other types of OL visualizations are > based on an image that is generated by the application server and > provided with layer information and other useful visualization stuff > in the xml file generated.
Close. By default (/ in the common case), OL has *no* interaction with XML -- only with images. It uses the local Javascript configuration to figure out how it should request those images. > Sorry if it is obvious, but i'm trying to figure out what i need and > if OL covers my purposes. Because I need to select some feature and > then with the information collected by a selection (with the mouse) > dialog with the server to do some operation on data. I wasn't clear enough before: There are always ways *around* the Same Origin Policy. Specifically, you can set up a proxy on any server that you're serving from, such that all requests go through a specific URL (which is local) which does the actual talking to the server. This is a reasonably common use case: this is why wfs.html shows points on http://openlayers.org/dev/examples/wfs.html , even though the points are from a remote server. > Do I need wfs-t for this or maybe is better to collect the data in non > httprequest-way and then treat the data as parameters for a query. I > mean: in wfs-t is there a simpler way to edit data than collecting all > the gids of the features and then building a query with these ids? Even if you did, unless you only wanted to see them (as an image) you would still need to make a request to get the raw feature data: You will need to use a Proxy, or host your HTML in the same "Origin" as your server: see http://en.wikipedia.org/wiki/Same_origin_policy . > >OpenLayers takes as a core tenet: "You can not talk to the server." > >This > >means you can't use XMLHttpRequest to do anything that is crucial to > >functionality unless there is no other way. All configuration, for > >example, is not taken from the WMS GetCapabilities, but is instead > >taken > >from local Javascript configuration -- duplicating information, but an > >unfortunate consequence of the Same Origin Policy. > > Probably I didn't understood how things go in OL. When I instantiate a > map and then a layer and then add a layer to the map, how goes the > communication with the WFS server? Relatively few maps have WFS servers in use. Most of them use WMS -- and in that case, the only communication is putting <img src="http://wms.example.com/"; /> tags into the page. For WFS, if the server is local, the server just uses XMLHttpRequest to open "/cgi-bin/mapserv?foo=bar" or what have you -- essentially, if you can form a valid relative URL to the server from the HTML page, you can talk to it with XMLHttpRequest. If the server is remote, a ProxyHost variable is set, which tells OpenLayers to send all its XMLHttpRequests through a single proxy first, which then passes on the request to the final destination. Does this help answer your questions? In general, I consider WFS a relative 'corner case' -- OpenLayers users seldom use it compared to the number of WMS users, for exactly the reasons you describe, so I apologize if my first email was less than clear. Regards, -- Christopher Schmidt MetaCarta _______________________________________________ Users mailing list [email protected] http://openlayers.org/mailman/listinfo/users
