之前加载的百度地图，偏移较大，一直没有再测试，于是将腾讯、高德、天地图的整理一下，方便查看。
腾讯js代码：
1 OpenLayers.Layer.QQ = OpenLayers.Class(OpenLayers.Layer.TileCache, { 2 sateTiles: !1, 3 initialize: function(a, b, c) { 4 var d = OpenLayers.Util.extend({ 5 format: "image/png", 6 isBaseLayer: !0 7 }, 8 c); 9 OpenLayers.Layer.TileCache.prototype.initialize.apply(this, [a, b, {}, 10 d]), 11 this.extension = this.format.split("/")[1].toLowerCase(), 12 this.extension = "jpg" == this.extension ? "jpeg": this.extension, 13 this.transitionEffect = "resize", 14 this.buffer = 0 15 }, 16 getURL: function(a) { 17 var b = this.map.getResolution(), 18 c = this.map.getMaxExtent(), 19 d = this.tileSize, 20 e = this.map.zoom, 21 f = Math.round((a.left - c.left) / (b * d.w)), 22 g = Math.round((c.top - a.top) / (b * d.h)), 23 h = new Array(0, 0, 0, 0, 0, 3, 0, 3, 0, 3, 0, 3, 0, 7, 0, 7, 0, 15, 0, 15, 0, 31, 0, 31, 0, 63, 4, 59, 0, 127, 12, 115, 0, 225, 28, 227, 356, 455, 150, 259, 720, 899, 320, 469, 1440, 1799, 650, 929, 2880, 3589, 1200, 2069, 5760, 7179, 2550, 3709, 11520, 14349, 5100, 7999, 23060, 28689, 10710, 15429, 46120, 57369, 20290, 29849, 89990, 124729, 41430, 60689, 184228, 229827, 84169, 128886), 24 i = 4 * e, 25 j = h[i++], 26 k = h[i++], 27 l = h[i++], 28 h = h[i], 29 m = this.sateTiles ? ".jpg": ".png"; 30 if (f >= j && k >= f && g >= l && h >= g) { 31 g = Math.pow(2, e) - 1 - g; 32 var n = 'z=' + e + '&x=' + f + '&y=' + g + '&type=vector&style=0&v=1.1.1' 33 } 34 var o = this.url; 35 return OpenLayers.Util.isArray(o) && n && (o = this.selectUrl(n, o)), 36 o + n 37 }, 38 clone: function(a) { 39 return null == a && (a = new OpenLayers.Layer.QQ(this.name, this.url, this.options)), 40 a = OpenLayers.Layer.TileCache.prototype.clone.apply(this, [a]) 41 }, 42 CLASS_NAME: "OpenLayers.Layer.QQ" 43 });