在这先说点题外话，本人在研究webgl 三维球过程中惊人发现，openlayers 的开发人员也在研究webgl并经证实他们也正在研发基于
webgl的三维gis开源平台，这可能是首个开源的三维平台，在现在三维大趋势下，看来 openlayers 前景还是一片大好，闲话少说，静候佳音。
在这将分4篇文章来系统的详细的介绍openlayers 是怎么来加载本地及服务器瓦片，为了提高开发人员的工作效率 采用倒叙，
在第一篇先给实用的算法及简单的参数说明，后面介绍原理，彻底的理解其工作原理。
第一篇 ：加载瓦片的算法类
第二篇 ：瓦片制作
第三篇 ：瓦片参数确定
第四篇 ：openlayers 加载的瓦片投影
第一篇加载瓦片的算法类
1、先给个类图简单的介绍下
我们在客户端看到的瓦片其实是一个图片列表 也就是上面的grid 类 ，每张图片都是通过http从后来请求过来的图片也就是方法getURL（bound），
每张图片都有自己的url 也就是他的请求地址，而且grid的列表的每个单元格都有边框也就是bound，那要获取每个单元格中正确的图片都是通过bound来计
算而获取到相应的图片，如想要加载自己瓦片就需要重写grid中的getURL(bound)方法，这也就是最下排6个不同类型的瓦片根据自己的瓦片特点及地图服务
的特点编写的类，如果你有自己的瓦片却跟上面的几种都不相同也不相似，那你可以选择重写grid类，如果你的瓦片操作跟下面的6中服务相同或者类似，那
可以根据自己工作考虑重写那面6个类中的其中某一个中的getURL(bound)的方法。在计算的过程中能涉及到多个参数将在下篇来详细介绍，在这给几个重写
getURL(bound)的例子, 第一个例子是网上的不过在工作中验证过，绝对可用，写的还不错给大家个参考。
1、重写grid类中的getURL(bound)方法加载本地图片(天地图)
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"
});
测试页面
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0">
<meta name="apple-mobile-web-app-capable" content="yes">
<title>OpenLayers Tiled Map Service Example</title>
<link rel="stylesheet" href="../theme/default/style.css" type="text/css">
<link rel="stylesheet" href="style.css" type="text/css">
<script src="../lib/OpenLayers.js"></script>
<script type="text/javascript"> var map, layer; function init(){
var extent = new OpenLayers.Bounds(-180.0, -90.0, 180.0, 90.0);
var tempScales = [295497593.05875003,147748796.52937502,73874398.264687508,36937199.132343754,18468599.566171877];
var mapOptions = {
maxExtent: extent
};
var options= {
mapType:"EMap",
topLevel: 3,
bottomLevel: 20 };
map = new OpenLayers.Map("map",mapOptions); layer = new OpenLayers.Layer.TiandituLayer("qincy", "http://tile0.tianditu.com/DataServer",options);
map.addLayer(layer);
map.addControls([new OpenLayers.Control.MousePosition()]); map.setCenter(new OpenLayers.LonLat(106,39), 3); }
</script>
</head>
<body onload="init()">
<div id="map" style="width:1000px;height:500px"></div>
</body>
</html>
2、重写TileCache类加载本地图片。
/**
* 对自定义规则切割的图片进行拼装的类
*/
SimpleTileCache=OpenLayers.Class(OpenLayers.Layer.TileCache,{
initialize:function(name,url,options){
var tempoptions = OpenLayers.Util.extend(
{'format': 'image/png',isBaseLayer:true},options);
OpenLayers.Layer.TileCache.prototype.initialize.apply(this,[name, url, {}, tempoptions]);
this.extension = this.format.split('/')[1].toLowerCase();
this.extension = (this.extension == 'jpg') ? 'jpeg' : this.extension;
this.transitionEffect="resize";
this.buffer=2;
},
/**
* 按地图引擎切图规则实现的拼接方式
*/
getURL: function(bounds) {
var res = this.map.getResolution();
var bbox = this.map.getMaxExtent();
var size = this.tileSize;
//计算列号
var tileX = Math.round((bounds.left - bbox.left) / (res * size.w));
//计算行号
var tileY = Math.round((bbox.top-bounds.top) / (res * size.h));
//当前的等级
var tileZ = this.map.zoom;
if(tileX<0) tileX=tileX+Math.round(bbox.getWidth()/bounds.getWidth());
if(tileY<0) tileY=tileY+Math.round(bbox.getHeight()/bounds.getHeight());
return this.getTilePic(tileX,tileY,tileZ);
},
getTilePic: function(tileX,tileY,tileZ){
var dir = '';
if(tileZ > 6) {
var delta = Math.pow(2,tileZ-5);
var rowDir = 'R'+ Math.floor(tileY /delta);
var colDir = 'C'+Math.floor(tileX /delta);
dir = tileZ + "/" + rowDir + "/" + colDir + "/";
} else {
dir= tileZ + '/';
}
var tileNo = tileZ + "-" + tileX + "-" + tileY;
var sUrl = this.url + dir + tileNo + '.png';
return sUrl;
},
clone: function (obj) {
if (obj == null) {
obj = new SimpleTileCache(this.name,this.url,this.options);
}
obj = OpenLayers.Layer.TileCache.prototype.clone.apply(this, [obj]);
return obj;
},
CLASS_NAME: "SimpleTileCache"
});
3、直接修改TileCache类中的getURL方法
修改后 的 TileCache.js
OpenLayers.Layer.TileCache = OpenLayers.Class(OpenLayers.Layer.Grid, {
isBaseLayer: true,
format: 'image/png',
serverResolutions: null,
initialize: function(name, url, layername, options) {
this.layername = layername;
OpenLayers.Layer.Grid.prototype.initialize.apply(this,
[name, url, {}, options]);
this.extension = this.format.split('/')[1].toLowerCase();
this.extension = (this.extension == 'jpg') ? 'jpeg' : this.extension;
},
clone: function (obj) {
if (obj == null) {
obj = new OpenLayers.Layer.TileCache(this.name,
this.url,
this.layername,
this.getOptions());
}
//get all additions from superclasses
obj = OpenLayers.Layer.Grid.prototype.clone.apply(this, [obj]);
// copy/set any non-init, non-simple values here
return obj;
},
getURL: function(bounds) {
var res = this.map.getResolution();
var x = Math.round ((bounds.left - this.maxExtent.left) / (res * this.tileSize.w));
var y = Math.round ((this.maxExtent.top - bounds.top) / (res * this.tileSize.h));
var z = this.map.getZoom();
var path =z+9+ "/" + x + "/" + y + "." + this.type;
var url = this.url;
if (url instanceof Array) {
url = this.selectUrl(path, url);
}
//我用resin 发布的地图瓦片的位置
url="http://192.168.0.90:88/roadmap2/"+path;
return url
},
/*getURL: function(bounds) {
var res = this.getServerResolution();
var bbox = this.maxExtent;
var size = this.tileSize;
var tileX = Math.round((bounds.left - bbox.left) / (res * size.w));
var tileY = Math.round((bounds.bottom - bbox.bottom) / (res * size.h));
var tileZ = this.serverResolutions != null ?
OpenLayers.Util.indexOf(this.serverResolutions, res) :
this.map.getZoom();
var components = [
this.layername,
OpenLayers.Number.zeroPad(tileZ, 2),
OpenLayers.Number.zeroPad(parseInt(tileX / 1000000), 3),
OpenLayers.Number.zeroPad((parseInt(tileX / 1000) % 1000), 3),
OpenLayers.Number.zeroPad((parseInt(tileX) % 1000), 3),
OpenLayers.Number.zeroPad(parseInt(tileY / 1000000), 3),
OpenLayers.Number.zeroPad((parseInt(tileY / 1000) % 1000), 3),
OpenLayers.Number.zeroPad((parseInt(tileY) % 1000), 3) + '.' + this.extension
];
var path = components.join('/');
var url = this.url;
if (OpenLayers.Util.isArray(url)) {
url = this.selectUrl(path, url);
}
url = (url.charAt(url.length - 1) == '/') ? url : url + '/'; //url+path
//alert(url+path);
return "http://192.168.0.90:88/roadmap/1/0/0.png"
},*/
CLASS_NAME: "OpenLayers.Layer.TileCache"
});
测试页面
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0">
<meta name="apple-mobile-web-app-capable" content="yes">
<title>OpenLayers TileCache Example</title>
<link rel="stylesheet" href="../theme/default/style.css" type="text/css">
<link rel="stylesheet" href="style.css" type="text/css">
<script src="../lib/OpenLayers.js"></script>
<script src="../lib/Firebug/firebug.js"></script>
<script type="text/javascript">
//alert("adsf");
var proj='EPSG:900913'; //900913
var map, layer;
var proj2 = new OpenLayers.Projection("EPSG:4326");
var agsTileOrigin = new OpenLayers.LonLat(-180,85);
agsTileOrigin.transform(proj2, new OpenLayers.Projection("EPSG:900913"));
//alert(agsTileOrigin.);
var mapExtent = new OpenLayers.Bounds(-20037508.34,-20037508.34,20037508.34,20037508.34);
function init(){ //添加编辑图层 图层名称为editLayer
var EditLayer=new OpenLayers.Layer.Vector("EidtLayer");
//添加地图
map = new OpenLayers.Map( 'map', {
numZoomLevels:3, //缩放级别
resolutions:[305.7481,152.8741,76.437], //分别率 单位是米
controls:[
new OpenLayers.Control.EditingToolbar(EditLayer), //添加编辑控件
new OpenLayers.Control.Navigation(),
new OpenLayers.Control.PanZoomBar(),
new OpenLayers.Control.LayerSwitcher({'ascending':false}),
new OpenLayers.Control.Permalink(),
new OpenLayers.Control.ScaleLine(),
new OpenLayers.Control.Permalink('permalink'),
new OpenLayers.Control.MousePosition(),
new OpenLayers.Control.OverviewMap(),
new OpenLayers.Control.KeyboardDefaults()
]
});
layer = new OpenLayers.Layer.TileCache("TileCache Layer",
"http://c0.tilecache.osgeo.org/wms-c/cache/",
"basic",
{
serverResolutions:[305.7481,152.8741,76.437],
projection:proj,
type:'png'
}
); map.addLayers([layer, EditLayer]);
var lob_ll=new OpenLayers.LonLat(121.34457, 31.329235);
map.setCenter(lob_ll.transform(proj2, new OpenLayers.Projection("EPSG:900913")), 0);
}
</script>
<style type="text/css">
html,body{width:100%;height:100%;margin:0;}
</style>
</head>
<body onload="init()">
<div id="map" class="smallmap" style="width:100%; height:100%; backround-color:Red;"></div>
</body>
</html>