百度地图TILE算法

var LLBAND2 = [75, 60, 45, 30, 15, 0];

var LL2MC2 = [[-.0015702102444, 111320.7020616939, 0x60e374c3105a3, -0x24bb4115e2e164, 0x5cc55543bb0ae8, -0x7ce070193f3784, 0x5e7ca61ddf8150, -0x261a578d8b24d0, 0x665d60f3742ca, 82.5], [.0008277824516172526, 111320.7020463578, 647795574.6671607, -4082003173.641316, 10774905663.51142, -15171875531.51559, 12053065338.62167, -5124939663.577472, 913311935.9512032, 67.5], [.00337398766765, 111320.7020202162, 4481351.045890365, -23393751.19931662, 79682215.47186455, -115964993.2797253, 97236711.15602145, -43661946.33752821, 8477230.501135234, 52.5], [.00220636496208, 111320.7020209128, 51751.86112841131, 3796837.749470245, 992013.7397791013, -1221952.21711287, 1340652.697009075, -620943.6990984312, 144416.9293806241, 37.5], [-.0003441963504368392, 111320.7020576856, 278.2353980772752, 2485758.690035394, 6070.750963243378, 54821.18345352118, 9540.606633304236, -2710.55326746645, 1405.483844121726, 22.5], [-.0003218135878613132, 111320.7020701615, .00369383431289, 823725.6402795718, .46104986909093, 2351.343141331292, 1.58060784298199, 8.77738589078284, .37238884252424, 7.45]];
function convertorLng(lng, cN) {
	var T = cN[0] + cN[1] * Math.abs(lng);
	T *= (lng < 0 ? -1 : 1);
	return T;
};
function convertorLat(lat, cN) {

	var cL = Math.abs(lat) / cN[9];
	var cO = cN[2] + cN[3] * cL + cN[4] * cL * cL + cN[5] * cL
			* cL * cL + cN[6] * cL * cL * cL * cL + cN[7] * cL
			* cL * cL * cL * cL + cN[8] * cL * cL * cL * cL
			* cL * cL;
	cO *= (lat < 0 ? -1 : 1);
	return cO;
};
function convertorLat2(lat, b) {

	d = Math.abs(lat) / b[9];
	d = b[2] + b[3] * d + b[4] * d * d + b[5] * d * d * d + b[6] * d * d * d * d + b[7] * d * d * d * d * d + b[8] * d * d * d * d * d * d;
	d = d * (0 >  lat ? -1 :1);
	return d;
};
function aa(lng2, lat2, c3) {
	//debugger;
	//var c3 = 18;
	var c1 = 256;
	//var lng = 12684092.41;
	//var lat = 2559234.49;

	var cL = -180;
	var T = 180;

	while (lng2 > T) {
		lng2 -= T - cL
	}
	while (cM < cL) {
		lng2 += T - cL
	}

	lat2 = Math.max(lat2, -74)
	lat2 = Math.min(lat2, 74)
	var cN;
	for (var cM = 0; cM < LLBAND2.length; cM++) {
		if (lat2 >= this.LLBAND2[cM]) {
			cN = this.LL2MC2[cM];
			break;
		}
	}
	if (!cN) {
		for (var cM = LLBAND2.length - 1; cM >= 0; cM--) {
			if (lat2 <= -LLBAND2[cM]) {
				cN = LL2MC2[cM];
				break
			}
		}
	}

	 
	 

	var lng = convertorLng(lng2, cN);
	var lat = convertorLat(lat2, cN);

	var cU = Math.pow(2, (18 - c3));
	var cX = Math.pow(2, (18 - c3)) * c1;
	var cV = Math.ceil(lng / cX);
	var cQ = Math.ceil(lat / cX);
	var cO = [cV, cQ, (lng - cV * cX) / cX * c1,
			(lat - cQ * cX) / cX * c1];
	var width = 0;
	var height = 0;
	var db = cO[0] - Math.ceil((width / 2 - cO[2]) / c1);
	var cN2 = cO[1] - Math.ceil((height / 2 - cO[3]) / c1);
	alert('http://online2.map.bdimg.com/tile/?qt=tile&x=' + db + '&y=' + cN2 + '&z=' + c3 + '&styles=pl&udt=20140314');

	return
}