function lng2map(lon) { return (((lon+180)/360*Math.pow(2,0))); }
function lat2map(lat)  { return (((1-Math.log(Math.tan(lat*Math.PI/180) + 1/Math.cos(lat*Math.PI/180))/Math.PI)/2 *Math.pow(2,0))); }

function svg_map(svg,p) { return new svg_map_obj(svg,p)  }

function svg_map_obj(svg,p) {
    var p = p ? p : {},
        x0 = p.x0 ? p.x0 : 0.1286,  // default x start location [0,1]
        y0 = p.y0 ? p.y0 : 0.33066,  // default y start location [0,1]
        zoom = p.zoom ? p.zoom : 6,  // default zoom at 6
        update_delay = p.update_freq ? p.update_freq :  50,   // How fast we look for new tiles
        zoom_delay = p.zoom_delay ? p.zoom_delay : 1000,      // How long we keep old tiles when zooming
        tiles = [], keepTiles = [],  // variables holding the tile ids
        mapLayer = svg.append("svg:g").attr("class","mapLayer"),
        viewBox = svg[0][0].viewBox.baseVal;
    
    function PixelWidthSVG()  { return svg[0][0].clientWidth ? svg[0][0].clientWidth  : svg[0][0].parentNode.clientWidth;}
    function PixelHeightSVG() { return svg[0][0].clientHeight ? svg[0][0].clientHeight : svg[0][0].parentNode.clientHeight;}

    function resize() {
        new_zoom = Math.floor(checkZoom());
        viewBox.width  = PixelWidthSVG() / (Math.pow(2,new_zoom)*256);
        viewBox.height = PixelHeightSVG()  / (Math.pow(2,new_zoom)*256);
        loadTiles();
    }
        
    checkZoom = function() {
            return Math.min(Math.max(Math.log(PixelWidthSVG()/(viewBox.width*256))/Math.log(2),0),18);
    }

    loadTiles = function() {
        new_zoom = Math.floor(checkZoom());
        if (zoom != new_zoom) {
            zoom = new_zoom;
            if (keepTiles.length == 0) {
                keepTiles = tiles.slice();
                setTimeout(function (){ keepTiles = []},1000)
            }
        }
        no_x = Math.floor(PixelWidthSVG()  / 256)+3;
        no_y = Math.floor(PixelHeightSVG()  / 256)+3;

        firstX = Math.max(Math.floor(viewBox.x * Math.pow(2,zoom)-1),0);
        firstY = Math.max(Math.floor(viewBox.y * Math.pow(2,zoom)-1),0);
      
        tiles = [];
        
        for (x=Math.max(firstX,0); x<Math.min(firstX+no_x,Math.pow(2,zoom));x++) {
            for (y=Math.max(firstY,0); y <Math.min(firstY+no_y,Math.pow(2,zoom));y++) {
                tiles.push({x:x,y:y,zoom:zoom});
            };
        };
        
        images = mapLayer.selectAll("image").data(tiles.concat(keepTiles),function(d) { return d.zoom+"/"+d.x+"/"+d.y;});
        images.enter()
            .append("svg:image")
            .attr("x",function(d) { return (d.x) / Math.pow(2,zoom);})
            .attr("y",function(d) { return (d.y)/ Math.pow(2,zoom);})
            .attr("height",1/Math.pow(2,zoom))
            .attr("width",1/Math.pow(2,zoom))
            .property("shape-rendering","crispEdges")
            .attr("xlink:href",function(d) { 
                    return "http://b.tile.cloudmade.com/"+p.api_key+"/1/256/"+zoom+"/"+d.x+"/"+d.y+".png";})
                    
        images.exit().remove();
    }
    svg.attr("viewBox",x0+" "+y0+" "+"0.1 0.1")
        .attr("preserveAspectRatio", "xMinYMin meet");  // Ensure a viewbox exists with fixed aspect ratio
    resize();
    setInterval(loadTiles,update_delay);  // Keep looking for new tiles and discard old
    svg.svg_map = {checkZoom:checkZoom,resize:resize,loadTiles:loadTiles};
    return svg.map_data;
}