[Openstreetmap] SVG, JavaScript, DOM, AJAX and web mapping

[SteveC]

* @ 05/07/05 07:57:53 PM richard at systemeD.net wrote:
> On 5 Jul 2005, at 15:20, Nick Whitelegg wrote:
> 
> >This is an interesting concept and got me wondering about how it could 
> >be
> >used for web mapping. An approach where...
> >
> >1) User navigates the map by pressing an arrow key, e.g. moves left
> >2) Client (JavaScript ) sends server an HTTP request for data in the 
> >new
> >grid square
> >3) Server sends back the data in the new grid square as XML embedded 
> >within
> >an HTTP response
> >4) JavaScript processes the data. Map is stored client-side as an SVG
> >document. JavaScript redraws the map by manipulating the Document 
> >Object
> >Model of the SVG.
> 
> This is very similar to what we're doing at waterscape.com, except with 
> Flash rather than SVG/JavaScript.
> 
> The user opens a page containing an SWF client (non-dynamic) which 
> sends the HTTP request for data in the new grid square, as per above. A 
> 'responder' script on the server sends back the data (in query string 
> format, not XML... my feelings on XML are roughly equivalent to 
> http://ex-parrot.com/~chris/sucks/trainwreck.html ).


I'm no fan of XML, but RSS and whatever perls problems are, arn't XMLs
problems.


> 
> This data comprises two things: a list of icons, each with grid 
> reference, and a list of waterways. The SWF client has all the icons 
> embedded in its 'symbol library', so can place these on the map 
> instantly. For the waterways, which are vector data, a further call to 
> the server results in a dynamically-generated SWF (courtesy of Ming, 
> ming.sourceforge.net) which can be overlaid on the map.
> 
> There's a third element of the map: the raster tiles, which form the 
> backdrop to all of this. These follow a consistent naming convention 
> and therefore can simply be loaded in as JPEGs directly from the 
> server, without any need to consult the responder.
> 
> The client<->server communication is pretty simple call-and-response 
> stuff. Flash actually has a much nicer facility for opening up sockets 
> and 'talking' on those, but unfortunately, most corporate firewalls 
> seem to block the port range chosen by Macromedia. Since our map has to 
> be accessible to the general consumer, this rules it out for us. 
> (That's also why we've used Flash rather than SVG.)
> 
> cheers
> Richard
> 
> 
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have fun,

SteveC steve at fractalus.com http://www.fractalus.com/steve/