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：
里面的数字与代码中是一样的。不过它的Level 0对应了代码中的Level 1。只有代码中这样设置，天地图才能加载得出来。不清楚是什么原因。也许当前（2021年4月）版本的天地图就是这样子的。
参考文章
GIS开发扫盲贴–地理坐标系
