Using Custom Tile Sources / Google-like Tile Layer Support

If you have tiles which are set up according to the 'Google' tile schema -- that is, based on x,y,z and starting in the upper left corner of the world -- you can load these tiles with the TMS layer with a slightly modified get_url function. (Note that in the past there was a 'LikeGoogle' layer in SVN -- this is the appropriate replacement for that code/functionality.)

First, define a getURL function that you want to use: it should accept a bounds as an argument, and will look something like this:

    function get_my_url (bounds) {
        var res = this.map.getResolution();
        var x = Math.round ((bounds.left - this.maxExtent.left) / (res * this.tileSize.w));
        var y = Math.round ((this.maxExtent.top - bounds.top) / (res * this.tileSize.h));
        var z = this.map.getZoom();

        var path = z + "/" + x + "/" + y + "." + this.type; 
        var url = this.url;
        if (url instanceof Array) {
            url = this.selectUrl(path, url);
        }
        return url + path;
        
    }

Then, when creating your TMS layer, pass in options like:

  new OpenLayers.Layer.TMS("Name", "http://example.com/", { 'type':'png', 'getURL':get_my_url });

This will cause the getURL function to be overridden by your function, thus requesting your inverted google-like tiles instead of standard TMS tiles.

Note that the map configuration options for a Google-like layer should be:

 {
   maxExtent: new OpenLayers.Bounds(-20037508.3427892,-20037508.3427892,20037508.3427892,20037508.3427892), 
   numZoomLevels:18, 
   maxResolution:156543.0339, 
   units:'m', 
   projection: "EPSG:900913",
   displayProjection: new OpenLayers.Projection("EPSG:4326")
 } 

To transform from WGS84 long/lat to mercator-projected meters as in the setCenter example:

  var lonLat = new OpenLayers.LonLat(-100, 40) ;
  lonLat.transform(map.displayProjection,map.getProjectionObject());
  map.setCenter(lonLat, 5);

This would center the map on WGS84 coordinates long -100 lat 40 at zoom level 5.

Note: Projection.js is available as "trunk" code until 2.6 becomes stable.