Openlayers离线加载天地图

概述：

经过一个春节的休整，今天终于开始了！不论什么时候，都不要忘记学习，学习是一辈子的事情！今天，我来说说如何实现天地图的离线以及Openlayers加载离线数据实现天地图数据的展示。

实现：

1、获取天地图的数据

可以通过网络上下载各大地图的工具将天地图的数据下载下来，并制作成mbtiles文件。制作过程在此就不详述，将已经制作好的一个文件上传到了百度网盘，需要的童鞋可以下载哦~~~~

下载链接：http://pan.baidu.com/s/1dEmNtnF 密码：xqd8

2、读取mbtiles并返回到页面

mbtiles其实就是一个sqllite数据库， 其详细可移步至http://www.cnblogs.com/i-gps/p/3919475.html查看详细。在此方案中，我用了一个servlet，具体的实现代码如下：

package com.lzugis.web;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * Created by Administrator on 2016/2/27.
 */
@WebServlet(description = "tian ditu tile", urlPatterns =  {"/tdttile"})
public class TiandituTile extends HttpServlet {
    private String tilepath = "D:/data/tdt/";
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String tile_column = request.getParameter("X");
        String tile_row = request.getParameter("Y");
        String zoom_level = request.getParameter("L");
        String layer = request.getParameter("T");
        // TODO Auto-generated method stub
        try {
            Class.forName("org.sqlite.JDBC");
        }
        catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            // e.printStackTrace();
            System.out.println("数据库驱动未找到!");
        }
        // 得到连接 会在你所填写的目录建一个你命名的文件数据库
        Connection conn;
        try {
            String conurl = "jdbc:sqlite:"+tilepath+layer+".mbtiles";
            conn = DriverManager.getConnection(conurl,null,null);
            // 设置自动提交为false
            conn.setAutoCommit(false);
            Statement stmt = conn.createStatement();
            //判断表是否存在
            ResultSet rsTables = conn.getMetaData().getTables(null, null, "tiles", null);
            if(!rsTables.next()){
                System.out.println("表不存在");
            }
            // 得到结果集
            String sql = "SELECT * FROM tiles WHERE zoom_level = "+zoom_level+
                    " AND tile_column = "+tile_column+
                    " AND tile_row = "+tile_row;
            ResultSet rs = stmt.executeQuery(sql);
            if(rs.next()) {
                byte[] imgByte = (byte[]) rs.getObject("tile_data");
                InputStream is = new ByteArrayInputStream(imgByte);
                OutputStream os = response.getOutputStream();
                try {
                    int count = 0;
                    byte[] buffer = new byte[1024 * 1024];
                    while ((count = is.read(buffer)) != -1) {
                        os.write(buffer, 0, count);
                    }
                    os.flush();
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    os.close();
                    is.close();
                }
            }
            else{
                System.out.println(sql);
                System.out.println("未找到图片！");
            }
            rs.close();
            conn.close();
        }
        catch (SQLException e) {
            e.printStackTrace();
            System.out.println("SQL异常!");
        }
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

其中，请求地址为：http://localhost:8081/lzugis/tdttile?T=vec_c&L=5&X=25&Y=3，请求的结果如下所示：

3、openlayers调用

从网上拔了下openlayers加载天地图的代码，并稍作修改，扩展了一个openlayers图层TiandituLayer，其代码如下：

OpenLayers.Layer.TiandituLayer = OpenLayers.Class(OpenLayers.Layer.Grid,{
	mapType : null,
	mirrorUrls : null,
	topLevel : null,
	bottomLevel : null,
	
	//用于标识是本地天地图切片库还是访问在线天地图
	isOnline:true,

	topLevelIndex : 0,
	bottomLevelIndex : 20,
	topTileFromX : -180,
	topTileFromY : 90,
	topTileToX : 180,
	topTileToY : -270,

	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.TiandituLayer(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 x_num = this.topTileFromX < this.topTileToX ? Math
				.round((bounds.left - this.topTileFromX) / coef) : Math
				.round((this.topTileFromX - bounds.right) / coef);
		var y_num = this.topTileFromY < this.topTileToY ? Math
				.round((bounds.bottom - this.topTileFromY) / coef)
				: Math.round((this.topTileFromY - bounds.top) / coef);

		var type = this.mapType;
		var url = this.url;
		if (this.mirrorUrls != null) {
			url = this.selectUrl(x_num, this.mirrorUrls);
		}
		return this.getFullRequestString({
			T : type,
			X : x_num,
			Y : y_num,
			L : level
		}, url);
	},
	getFullRequestString: function(params, url){
		url = url+'?T='+params.T+'&L='+params.L+'&X='+params.X+'&Y='+params.Y;
		return 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)
	},
	CLASS_NAME : "OpenLayers.Layer.TiandituLayer"
}); 

在代码中新建一个TiandituLayer，并添加到map中即可实现，代码如下：

<!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 MapQuest Demo</title>
    <link rel="stylesheet" href="../../../../plugin/OpenLayers-2.13.1/theme/default/style.css" type="text/css">
    <script src="../../../../plugin/OpenLayers-2.13.1/OpenLayers.js"></script>
    <script src="TiandituLayer-src.js"></script>
    <style type="text/css">
        html, body, #map{
            padding:0;
            margin:0;
            height:100%;
            100%;
            overflow: hidden;
        }
    </style>
    <script type="text/javascript">
        var map;
        function init(){
            var vec_c = new OpenLayers.Layer.TiandituLayer("vec_c", "http://localhost:8081/lzugis/tdttile",{
                mapType:"vec_c",
                topLevel: 2,
                bottomLevel: 10,
                isBaseLayer:true,
                isOnline:false
            });
            var cva_c = new OpenLayers.Layer.TiandituLayer("cva_c", "http://t0.tianditu.com/DataServer",{
                mapType:"cva_c",
                topLevel: 0,
                bottomLevel: 18,
                isBaseLayer:false,
                isOnline:true
            });
            map = new OpenLayers.Map({
                div: "map",
                projection: "EPSG:4326",
                layers: [cva_c,vec_c,img_c],
                numZoomLevels:20,
                center: [103.847, 36.0473],
                zoom: 2
            });
            map.addControl(new OpenLayers.Control.LayerSwitcher());
            map.addControl(new OpenLayers.Control.MousePosition());
        }
    </script>
</head>
<body onload="init()">
<div id="map"></div>
</body>

说明：

1、代码中vec_c为天地图矢量层，cva_c为天地图标注层，与天地图的名称相一致；

2、vec_c为离线的地图，cva_c为在线的，通过参数isOnline区分其为离线还是在线；

完成后效果：