// making this a global variable so that it is accessible for
// debugging/inspecting in Firebug
var map = null;

function get_osm_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 limit = Math.pow(2, z);
	
	if (y < 0 || y >= limit)
	{
		return null;
	}
	else
	{
		x = ((x % limit) + limit) % limit;
		
		var path = z + "/" + x + "/" + y + "." + this.type; 
		var url = this.url;
		if (url=="http://tah.openstreetmap.org/~ojw/Tiles/cycle.php/") {
			if (z<12) url="http://tah.openstreetmap.org/~ojw/Tiles/cycle.php/"
			else url="http://tah.openstreetmap.org/Tiles/tile/"
		}
		if (url instanceof Array) {
			url = this.selectUrl(path, url);
		}
		return url + path;
	}
}