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我以往使用arcgis for js 3.19加载天地图，使用的都是默认的坐标系：4326。现在因为客户提供的地图，都是4490的，没办法，只能全部使用4490，否则不同坐标系的图层，没办法叠在一起。

4490是CGCS2000坐标系的WKID，4326是WGS84的WKID。有关它们的区别与联系，请阅读尾部的参考文章。有说法称，4490比4326更适合我们多一些。

以下是加载天地图的完整代码，写成了arcgis插件的形式：

define(["dojo/_base/declare","esri/layers/tiled"],function(declare) {
   	return declare(esri.layers.TiledMapServiceLayer, {
   		constructor: function(path, option) {
   			this.baseUrl = path;			this.layerType = option ? option.mode : null;			if(option.name){
   				this.id = option.name;			}			this.tk = getTk(option);			this.spatialReference = new esri.SpatialReference({
   				wkid: 4490			});			this.initialExtent = (this.fullExtent = new esri.geometry.Extent(45.0, -27.0, 163.0,45.0,				this.spatialReference));//中国及周边范围			this.tileInfo = getTileInfo();			this.loaded = true;			this.onLoad(this);						function getTk(option){
   				var tk;								if(option.tk){
   					tk = option.tk;				} else {
   					console.error("欠缺天地图的TK！！！");				}								return tk;			}			function getTileInfo(){
   				return new esri.layers.TileInfo({
   					/*						titleInfo可从图层中获取					*/					"dpi": 96,					"rows": 256,					"cols": 256,					"compressionQuality": 0,					"origin": {
   						x: -180,						y: 90					},					"spatialReference": {
   						"wkid": 4490,						"latestWkid": 4490					},					/*						scale:比例尺 ，resolution:分辨率					*/    					"lods": [ 						{
    level: 0, resolution: 1.40625, scale: 590995197.14166909755553014475 },						{
   							"level": 1,							"resolution": 0.7031250000000002,							"scale": 2.9549759305875003E8						},						{
   							"level": 2,							"resolution": 0.3515625000000001,							"scale": 1.4774879652937502E8						},						{
   							"level": 3,							"resolution": 0.17578125000000006,							"scale": 7.387439826468751E7						},						{
   							"level": 4,							"resolution": 0.08789062500000003,							"scale": 3.6937199132343754E7						},						{
   							"level": 5,							"resolution": 0.043945312500000014,							"scale": 1.8468599566171877E7						},						{
   							"level": 6,							"resolution": 0.021972656250000007,							"scale": 9234299.783085939						},						{
   							"level": 7,							"resolution": 0.010986328125000003,							"scale": 4617149.891542969						},						{
   							"level": 8,							"resolution": 0.005493164062500002,							"scale": 2308574.9457714846						},						{
   							"level": 9,							"resolution": 0.002746582031250001,							"scale": 1154287.4728857423						},						{
   							"level": 10,							"resolution": 0.0013732910156250004,							"scale": 577143.7364428712						},						{
   							"level": 11,							"resolution": 6.866455078125002E-4,							"scale": 288571.8682214356						},						{
   							"level": 12,							"resolution": 3.433227539062501E-4,							"scale": 144285.9341107178						},						{
   							"level": 13,							"resolution": 1.7166137695312505E-4,							"scale": 72142.9670553589						},						{
   							"level": 14,							"resolution": 8.583068847656253E-5,							"scale": 36071.48352767945						},						{
   							"level": 15,							"resolution": 4.2915344238281264E-5,							"scale": 18035.741763839724						},						{
   							"level": 16,							"resolution": 2.1457672119140632E-5,							"scale": 9017.870881919862						},						{
   							"level": 17,							"resolution": 1.0728836059570316E-5,							"scale": 4508.935440959931						},						{
   							"level": 18,							"resolution": 5.364418029785158E-6,							"scale": 2254.4677204799655						}					]				});            			}		}, //end of constructor		baseUrl: null,		layerType: null,		tk: null,		id:null,		getTileUrl: function (level, row, col) {
   			return this.baseUrl 				+ "?SERVICE=WMTS&REQUEST=GetTile&VERSION=1.0.0&STYLE=default&TILEMATRIXSET=c&FORMAT=tiles"				+ "&LAYER=" + this.layerType 				+ "&TILEMATRIX=" + level 				+ "&TILEROW=" + row 				+ "&TILECOL=" + col 				+ "&tk=" + this.tk;		}	});});

代码中，

"lods": [ 			{
    level: 0, resolution: 1.40625, scale: 590995197.14166909755553014475 },			{
   				"level": 1,				"resolution": 0.7031250000000002,				"scale": 2.9549759305875003E8			},

这部分比较神秘。我也不能确定这是啥，但从许多4490图层的信息来看，这应该是一种类似地图切片的方案或比例尺之类。你看，以下是一幅4490坐标系的底图：

参考文章

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