openlayer加载瓦片图，判断url各属性

1、重写grid类中的getURL(bound)方法加载本地图片(天地图)
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OpenLayers.Layer.TiandituLayer = OpenLayers.Class(OpenLayers.Layer.Grid,
{
TileType : null,
mirrorUrls : null,
topLevel : null,
bottomLevel : null,
topLevelIndex : 0,
bottomLevelIndex : 20,
topTileFromX : -180,
topTileFromY : 90,
topTileToX : 180,
topTileToY : -90,
isBaseLayer : true,
initialize : function(name, url, options) {
options.topLevel = options.topLevel ? options.topLevel
: this.topLevelIndex;
options.bottomLevel = options.bottomLevel ? options.bottomLevel
: this.bottomLevelIndex;
options.maxResolution = this
.getResolutionForLevel(options.topLevel);
options.minResolution = this
.getResolutionForLevel(options.bottomLevel);
var newArguments = [ name, url, {}, options ];
OpenLayers.Layer.Grid.prototype.initialize.apply(this,
newArguments);
},
clone : function(obj) {
if (obj == null) {
obj = new OpenLayers.Layer.TDTLayer(this.name, this.url,
this.options);
}
obj = OpenLayers.Layer.Grid.prototype.clone
.apply(this, [ obj ]);
return obj;
},
getURL : function(bounds) {
var level = this.getLevelForResolution(this.map.getResolution());
var coef = 360 / Math.pow(2, level);
var Row = this.topTileFromX < this.topTileToX ? Math.round((bounds.left - this.topTileFromX) / coef) : Math.round((this.topTileFromX - bounds.right) / coef);
var Col = this.topTileFromY < this.topTileToY ? Math.round((bounds.bottom - this.topTileFromY) / coef): Math.round((this.topTileFromY - bounds.top) / coef);
var type = this.TileType;
if (type == “EMap”) {
if (level >= 2 && level <= 10) {
type = “A0512_EMap”;
} else if (level == 11 || level == 12) {
type = “B0627_EMap1112”;
} else if (level >= 13 && level <= 18) {
type = “siwei0608”;
}
}else if(type==“RMap”){
if (level >= 2 && level <= 7) {
type = “sbsm0210”;
} else if (level >= 8 && level <= 10) {
type = “sbsm0210”;
} else if (level >= 11 && level <= 14) {
type = “e11”;
}else if (level >= 15 && level <= 18) {
type = “sbsm1518”;
}
}
var url = this.url;
if (this.mirrorUrls != null) {
url = this.selectUrl(Row, this.mirrorUrls);
}
return this.getFullRequestString({
T : type,
X : Row,
Y : Col,
L : level
}, url);
},
selectUrl : function(a, b) {
return b[a % b.length]
},
getLevelForResolution : function(res) {
var ratio = this.getMaxResolution() / res;
if (ratio < 1)
return 0;
for ( var level = 0; ratio / 2 >= 1;) {
level++;
ratio /= 2;
}
return level;
},
getResolutionForLevel : function(level) {
return 360 / 256 / Math.pow(2, level);
},
getMaxResolution : function() {
return this.getResolutionForLevel(this.topLevelIndex)
},
getMinResolution : function() {
return this.getResolutionForLevel(this.bottomLevelIndex)
},
addTile : function(bounds, position) {
var url = this.getURL(bounds);
return new OpenLayers.Tile.Image(this, position, bounds, url,
this.tileSize);
},
CLASS_NAME : “OpenLayers.Layer.TiandituLayer”
});

摘自 https://zhidao.baidu.com/question/1770360129860925900.html