tile_naming_algorithms.js

var mapBounds = new OpenLayers.Bounds(	-20037508.34, -20037508.34,
										 20037508.34,  20037508.34);		

/*
	Converts TMS tile coordinates to Microsoft QuadTree.
*/
function tmsToQuadTree(/* int */ tx, /* int */ ty, /* int */ zoom) {
	var quadKey = []; 
	
	// ISSUE: When using VirtualEarth or Google, need to put a '0' before the quadkey 
	// to compensate for those providers zoom level being reported as 0.
	// When using CloudMade, the 0 is correctly calculated.
	if( typeof window.QUADKEY_INITIAL_HACK == "number" ) { 
            quadKey.push( window.QUADKEY_INITIAL_HACK ); 
        }
	
	ty = ( Math.pow(2, zoom) - 1 ) - ty;
	for (var i = zoom; i > 0; i--) {
		var digit = 0;
		var mask = 1 << (i - 1);
		if ((tx & mask) != 0)
			digit += 1;
		if ((ty & mask) != 0)
			digit += 2;
		quadKey.push(digit);
	}
	return quadKey.join("");
}

/*
	Given a bounds object, return the 
	full URL path to the tile using the 
	Microsoft Quadtree organisation.
*/
function getQuadTreeURL( bounds, layer ) {
	var tms 	= getTMS( bounds, layer ),
	    quadKey	= tmsToQuadTree( tms.x, tms.y, tms.z ),
	    // layer.type -> 'png'
	    path	= quadKey + "." + layer.type,
	    // layer.url -> '/haiti/tiles/'
	    url 	= layer.url + path;
	
	return url;
}

/*
	Return x, y, z position for a tile 
	using the TMS specification.
*/
function getTMS( bounds, layer ) {
	bounds = layer.adjustBounds(bounds);
	var res = layer.map.getResolution(),
	    x = Math.round((bounds.left - layer.tileOrigin.lon) / (res * layer.tileSize.w)),
	    y = Math.round((bounds.bottom - layer.tileOrigin.lat) / (res * layer.tileSize.h)),
	    z = layer.map.getZoom();
	
	return { x:x, y:y, z:z };
}

/*
	Given a bounds object and map layer, return the full URL 
	path for the tile using the TMS specification.
*/
function getTMSURL( bounds, layer ) {
	var tms = getTMS( bounds, layer );
	var path = layer.serviceVersion + "/" + layer.layername + "/" + tms.z + "/" + tms.x + "/" + tms.y + "." + layer.type;
	var url = layer.url;
	
	if ( mapBounds.intersectsBounds( bounds ) && tms.z >= mapMinZoom && tms.z <= mapMaxZoom) {
	   return layer.url + path;
	} else {
	   return "http://localhost/none.png";
	}
}

/*
	This is passed to an instance of OpenLayers.Layer.TMS
	to provide a URL for a single tile.
*/
function getURL( bounds ) {
	//var url = getTMSURL( bounds, this );
	var url = getQuadTreeURL( bounds, this );
	return url;
}