[OSM-dev] Projection Issues

Christopher Schmidt crschmidt at crschmidt.net
Wed May 31 19:30:23 BST 2006


On Wed, May 31, 2006 at 06:45:35PM +0100, Nick Whitelegg wrote:
> >At this point, I'm largely just confused, and I'm willing to
> >admit that I think with the current setup, OSM and OpenLayers simply
> >aren't going to work together. I don't claim to understand projections
> >well enough to know what's going on, and without knowing that, I can't
> >begin to create a tile system that will grab tiles in the same format as
> >OSM currently is.
> 
> Having seen this talk of OpenLayers, I was going to experiment with it 
> this evening to see if it will talk to the new renderer (see recent dev 
> posts). Will OpenLayers accept the URL of a simple WMS-compliant server 
> i.e. a script which accepts bbox, width, height and layers parameters? I 
> note that the examples e.g. the Boston Free Map take a ".map" file which 
> is (I believe) a configuration file for Mapserver, but presumably 
> OpenLayers will talk to any WMS server.

Yep. The mapfile is just a configuration file, but OL will talk to any
WMS. 

The problem I was having with the new renderer is a 'zoom' parameter,
which I wasn't sure what effect it had :) But it does seem that the new
dev renderer works fine in OL:

http://crschmidt.net/projects/openstreetmap/devrender

The only modification I had to make to the OL code was to change bbox to
BBOX, etc.: Capitalizing keys in the URL request. Note that this is
against the WMS spec -- params are case insensitive -- so you should
probably just lowercase or uppercase all your param values, with
something like : 

foreach(array_keys($_GET) as $key) {
    $_GET[strtoupper($key)] = $_GET[$key];
}

to be compatible with as many WMS clients as possible. (Is this code in
SVN? I couldn't find it, or I'd have attached a patch.)

In any case, if this new renderer is actually going to be deployed in
the relatively near future, messing around with any of the other code is
probably not worthwhile.

-- 
Christopher Schmidt
Web Developer




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