查找最近距离geohash算法（增加周边邻近编号）

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查找最近距离geohash算法（增加周边邻近编号）

2024-10-23 23:00:02 212人阅读

接着上一篇文章：查找附近网点geohash算法及实现（Java版本） http://blog.csdn.net/sunrise_2013/article/details/42024813

参考文档：

http://www.slideshare.net/sandeepbhaskar2/geohash 介绍geohash原理及例子

http://geohash.gofreerange.com/ 演示实例

http://geohash.gofreerange.com/ 周边8格子实例

由于存在部分网点丢失的情况，为了解决边缘问题，需要计算这个块周围的八个格子，补充代码，实现周边8个编码的最近编码。

根据一个geohash值获取周围8个geohash值的代码。

例如在方格4的左下部分的点和大方格1的右下部分的点离的很近，可是它们的geohash值一定是相差的相当远，因为头一次的分块就相差太大了，很多时候我们对geohash的值进行简单的排序比较，结果貌似真的能够找出相近的点，并且似乎还是按照距离的远近排列的，可是实际上会有一些点被漏掉了。
上述这个问题，可以通过搜索一个格子，周围八个格子的数据，统一获取后再进行过滤。这样就在编码层次解决了这个问题。

技术分享

主要代码：

<span style="font-family: Arial, Helvetica, sans-serif;">public static String[] getGeoHashExpand(String geohash) {</span></span>

 		try {
 			String geohashTop = calculateAdjacent(geohash, TOP);
 			String geohashBottom = calculateAdjacent(geohash, BOTTOM);
 			String geohashRight = calculateAdjacent(geohash, RIGHT);
 			String geohashLeft = calculateAdjacent(geohash, LEFT);
 	
 			String geohashTopLeft = calculateAdjacent(geohashLeft, TOP);
 			String geohashTopRight = calculateAdjacent(geohashRight, TOP);
 			String geohashBottomRight = calculateAdjacent(geohashRight, BOTTOM);
 			String geohashBottomLeft = calculateAdjacent(geohashLeft, BOTTOM);
 	
 			String[] expand = { geohash, geohashTop, geohashBottom, geohashRight, geohashLeft, geohashTopLeft,
 					geohashTopRight, geohashBottomRight, geohashBottomLeft };
 			return expand;
 		} catch (Exception e) {
 			//logger.error("GeoHash Error",e);
 			return null;
 		}
 	}

</pre><pre code_snippet_id="571887" snippet_file_name="blog_20150105_5_8338259" name="code" class="java">

public static String calculateAdjacent(String srcHash, int dir) {
             srcHash = srcHash.toLowerCase();
             char lastChr = srcHash.charAt(srcHash.length() - 1);
             int type = (srcHash.length() % 2) == 1 ? ODD : EVEN;
             String base = srcHash.substring(0, srcHash.length() - 1);
             if (BORDERS[dir][type].indexOf(lastChr) != -1) {
                     base = calculateAdjacent(base, dir);
             }
             return base + BASE32.charAt(NEIGHBORS[dir][type].indexOf(lastChr));
     }

全部代码实例：

Geohase.java

package com.DistTest;

//Geohash.java
//Geohash library for Java
//ported from David Troy's Geohash library for Javascript
//- http://github.com/davetroy/geohash-js/tree/master
//(c) 2008 David Troy
//(c) 2008 Tom Carden
//Distributed under the MIT License

public class Geohash {

     public static int BITS[] = { 16, 8, 4, 2, 1 };

     public static String BASE32 = "0123456789bcdefghjkmnpqrstuvwxyz";

     public static int RIGHT = 0;
     public static int LEFT = 1;
     public static int TOP = 2;
     public static int BOTTOM = 3;

     public static int EVEN = 0;
     public static int ODD = 1;

     public static String[][] NEIGHBORS;
     public static String[][] BORDERS;

     static {
             NEIGHBORS = new String[4][2];
             BORDERS = new String[4][2];

             NEIGHBORS[BOTTOM][EVEN] = "bc01fg45238967deuvhjyznpkmstqrwx";
             NEIGHBORS[TOP][EVEN] = "238967debc01fg45kmstqrwxuvhjyznp";
             NEIGHBORS[LEFT][EVEN] = "p0r21436x8zb9dcf5h7kjnmqesgutwvy";
             NEIGHBORS[RIGHT][EVEN] = "14365h7k9dcfesgujnmqp0r2twvyx8zb";

             BORDERS[BOTTOM][EVEN] = "bcfguvyz";
             BORDERS[TOP][EVEN] = "0145hjnp";
             BORDERS[LEFT][EVEN] = "prxz";
             BORDERS[RIGHT][EVEN] = "028b";

             NEIGHBORS[BOTTOM][ODD] = NEIGHBORS[LEFT][EVEN];
             NEIGHBORS[TOP][ODD] = NEIGHBORS[RIGHT][EVEN];
             NEIGHBORS[LEFT][ODD] = NEIGHBORS[BOTTOM][EVEN];
             NEIGHBORS[RIGHT][ODD] = NEIGHBORS[TOP][EVEN];

             BORDERS[BOTTOM][ODD] = BORDERS[LEFT][EVEN];
             BORDERS[TOP][ODD] = BORDERS[RIGHT][EVEN];
             BORDERS[LEFT][ODD] = BORDERS[BOTTOM][EVEN];
             BORDERS[RIGHT][ODD] = BORDERS[TOP][EVEN];
     }

     private static void refine_interval(double[] interval, int cd, int mask) {
             if ((cd & mask) > 0) {
                     interval[0] = (interval[0] + interval[1]) / 2.0;
             } else {
                     interval[1] = (interval[0] + interval[1]) / 2.0;
             }
     }

     public static String calculateAdjacent(String srcHash, int dir) {
             srcHash = srcHash.toLowerCase();
             char lastChr = srcHash.charAt(srcHash.length() - 1);
             int type = (srcHash.length() % 2) == 1 ? ODD : EVEN;
             String base = srcHash.substring(0, srcHash.length() - 1);
             if (BORDERS[dir][type].indexOf(lastChr) != -1) {
                     base = calculateAdjacent(base, dir);
             }
             return base + BASE32.charAt(NEIGHBORS[dir][type].indexOf(lastChr));
     }
     
     
     

 	public static String[] getGeoHashExpand(String geohash) {
 		try {
 			String geohashTop = calculateAdjacent(geohash, TOP);
 			String geohashBottom = calculateAdjacent(geohash, BOTTOM);
 			String geohashRight = calculateAdjacent(geohash, RIGHT);
 			String geohashLeft = calculateAdjacent(geohash, LEFT);
 	
 			String geohashTopLeft = calculateAdjacent(geohashLeft, TOP);
 			String geohashTopRight = calculateAdjacent(geohashRight, TOP);
 			String geohashBottomRight = calculateAdjacent(geohashRight, BOTTOM);
 			String geohashBottomLeft = calculateAdjacent(geohashLeft, BOTTOM);
 	
 			String[] expand = { geohash, geohashTop, geohashBottom, geohashRight, geohashLeft, geohashTopLeft,
 					geohashTopRight, geohashBottomRight, geohashBottomLeft };
 			return expand;
 		} catch (Exception e) {
 			//logger.error("GeoHash Error",e);
 			return null;
 		}
 	}
     

     public static double[][] decode(String geohash) {
             boolean is_even = true;
             double[] lat = new double[3];
             double[] lon = new double[3];

             lat[0] = -90.0;
             lat[1] = 90.0;
             lon[0] = -180.0;
             lon[1] = 180.0;
             double lat_err = 90.0;
             double lon_err = 180.0;

             for (int i = 0; i < geohash.length(); i++) {
                     char c = geohash.charAt(i);
                     int cd = BASE32.indexOf(c);
                     for (int j = 0; j < BITS.length; j++) {
                             int mask = BITS[j];
                             if (is_even) {
                                     lon_err /= 2.0;
                                     refine_interval(lon, cd, mask);
                             } else {
                                     lat_err /= 2.0;
                                     refine_interval(lat, cd, mask);
                             }
                             is_even = !is_even;
                     }
             }
             lat[2] = (lat[0] + lat[1]) / 2.0;
             lon[2] = (lon[0] + lon[1]) / 2.0;

             return new double[][] { lat, lon };
     }

     public static String encode(double latitude, double longitude) {
             boolean is_even = true;
             int i = 0;
             double lat[] = new double[3];
             double lon[] = new double[3];
             int bit = 0;
             int ch = 0;
             int precision = 12;
             String geohash = "";

             lat[0] = -90.0;
             lat[1] = 90.0;
             lon[0] = -180.0;
             lon[1] = 180.0;

             while (geohash.length() < precision) {
                     if (is_even) {
                             double mid = (lon[0] + lon[1]) / 2.0;
                             if (longitude > mid) {
                                     ch |= BITS[bit];
                                     lon[0] = mid;
                             } else {
                                     lon[1] = mid;
                             }
                     } else {
                             double mid = (lat[0] + lat[1]) / 2.0;
                             if (latitude > mid) {
                                     ch |= BITS[bit];
                                     lat[0] = mid;
                             } else {
                                     lat[1] = mid;
                             }
                     }
                     is_even = !is_even;
                     if (bit < 4) {
                             bit++;
                     } else {
                             geohash += BASE32.charAt(ch);
                             bit = 0;
                             ch = 0;
                     }
             }
             return geohash;
     }

}

测试实例：

package com.DistTest;
  
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Connection;
import java.sql.Statement;
 
 
public class sqlTest {
	
        public static void main(String[] args) throws Exception {
        Connection conn = null;
        String sql;
        String sql1;
        String url = "jdbc:mysql://132.97.194.62/test?"
                + "user=root&password=sheng&useUnicode=true&characterEncoding=UTF8";
 
        try {
            Class.forName("com.mysql.jdbc.Driver");// 动态加载mysql驱动
            // System.out.println("成功加载MySQL驱动程序");
            // 一个Connection代表一个数据库连接
            conn = DriverManager.getConnection(url);
            // Statement里面带有很多方法，比如executeUpdate可以实现插入，更新和删除等
            Statement stmt = conn.createStatement();
                               
	  	    double lon1=109.0145193757;  
	  	    double lat1=34.236080797698;
	  	    //根据地理坐标，生成geohash编码
      	   // Geohash ghash = new Geohash();
    	   // String gcode=Geohash.encode(lat1, lon1).substring(0, 4);
      	    String gcode="wqj6z";
      	    
      	    String[] neargcode=Geohash.getGeoHashExpand(gcode);
      	    
	      	  for(int i=0;i<neargcode.length;i++)
	      	{
	      		System.out.println(neargcode[i]);
	      	}

            sql = "select * from retailersinfotable where geohash like "
            		+ "'"+neargcode[0]+"%' or '"+neargcode[1]+"%' or '"+neargcode[2]+"%' "
            		+ "or '"+neargcode[3]+"%' or '"+neargcode[4]+"%' or '"+neargcode[5]+"%' "
            		+ "or '"+neargcode[6]+"%' or '"+neargcode[7]+"%' or '"+neargcode[8]+"%'";
            System.out.println(sql);
            ResultSet rs = stmt.executeQuery(sql);// executeQuery会返回结果的集合，否则返回空值
            rs.last();
            int rowCount = rs.getRow(); //获得ResultSet的总行数
            System.out.println(rowCount);
            rs.beforeFirst();
            
            System.out.println("当前位置：经度"+lon1+" 维度："+lat1);
            int i=0;
    		String[][] array = new String[rowCount][3];
            while (rs.next()){
            		//从数据库取出地理坐标
            		double lon2=Double.parseDouble(rs.getString("Longitude"));
            		double lat2=Double.parseDouble(rs.getString("Latitude"));
            		
            		//根据地理坐标，生成geohash编码
	          	    Geohash geohash = new Geohash();
	        	    String geocode=geohash.encode(lat2, lon2).substring(0, 9);
	        	    
	        	    //计算两点间的距离
	      	        int dist=(int) Test.GetDistance(lon1, lat1, lon2, lat2); 
	      	        
	      			array[i][0]=String.valueOf(i);
	    			array[i][1]=geocode;
	    			array[i][2]=Integer.toString(dist);
	      			
	      			i++;
        
            	//	System.out.println(lon2+"---"+lat2+"---"+geocode+"---"+dist);	
                }

            array=sqlTest.getOrder(array); //二维数组排序
            sqlTest.showArray(array);        //打印数组

            
            
            
        } catch (SQLException e) {
            System.out.println("MySQL操作错误");
            e.printStackTrace();
        } finally {
            conn.close();
        }
 
    } 
    /*
     * 二维数组排序，比较array[][2]的值，返回二维数组
     * */
    public static String[][] getOrder(String[][] array){
		for (int j = 0; j < array.length ; j++) {
			for (int bb = 0; bb < array.length - 1; bb++) {
				String[] ss;
				int a1=Integer.valueOf(array[bb][2]);  //转化成int型比较大小
				int a2=Integer.valueOf(array[bb+1][2]);
				if (a1>a2) {
					ss = array[bb];
					array[bb] = array[bb + 1];
					array[bb + 1] = ss;
					
				}
			}
		} 
		return array;
    }
    
    /*打印数组*/
    public static void showArray(String[][] array){
    	  for(int a=0;a<array.length;a++){
      		for(int j=0;j<array[0].length;j++)
      			System.out.print(array[a][j]+" ");
      		System.out.println();
      	}
    }

 /*   public static void main(String[] args)
    {
    	String aaa="wxsfdf";
    	Geohash geohash = new Geohash();
    	String[] str = geohash.getGeoHashExpand(aaa);
    	for(int i=0;i<str.length;i++)
    	{
    		System.out.println(str[i]);
    	}
    
    }*/
    
}

查找最近距离geohash算法（增加周边邻近编号）

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