高德地圖變相實現簡單的地理圍欄技術

代碼地址：

• 前端：https://github.com/poemp/geo-fencing-frontend
• 後端：https://github.com/poemp/geo-fencing-frontend

原理

開發 -> Web服務 API -> 開發指南 -> API文檔 -> 地理圍欄

使用規則

配置好數據庫

global:
  datasource:
    service:
      type: com.alibaba.druid.pool.DruidDataSource
      driver-class-name: com.mysql.cj.jdbc.Driver
      url: jdbc:mysql://90service:2019/geo-fencing?useUnicode=true&characterEncoding=UTF-8&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=Asia/Shanghai
      username: root
      password: 123456 
  geo-fencing-backend:
    server-name: geo-fencing-backend
    port: 8081

配置前端地址：

const url = 'http://192.168.30.95:8081'; 
export default {url}

啓動前端：

使用命令 

npm start

瀏覽器打開地址 http://localhost:3333/#/ 可以查看界面

啓動後端

配置好數據庫後，啓動系統

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class GeoFencingBackendApplication {

    public static void main(String[] args) {
        SpringApplication.run(GeoFencingBackendApplication.class, args);
    }

}

使用

打開界面後，首先點擊編輯圍欄

開始畫區域，雙擊鼠標完成畫圖，點擊結束編輯圍欄後，數據後傳輸到後臺

最後，拖動座標，可以查看座標是不是在多邊形裏面。

核心算法

import java.awt.geom.Point2D;
import java.util.List;

public class InOrOutPolygonUtils {

    /**
     * 判斷點是否在多邊形內
     * @param point 檢測點
     * @param pts   多邊形的頂點
     * @return      點在多邊形內返回true,否則返回false
     */
    public static boolean IsPtInPoly(Point2D.Double point, List<Point2D.Double> pts){

        int N = pts.size();
        boolean boundOrVertex = true; //如果點位於多邊形的頂點或邊上，也算做點在多邊形內，直接返回true
        int intersectCount = 0;//cross points count of x
        double precision = 2e-10; //浮點類型計算時候與0比較時候的容差
        Point2D.Double p1, p2;//neighbour bound vertices
        Point2D.Double p = point; //當前點

        p1 = pts.get(0);//left vertex
        for(int i = 1; i <= N; ++i){//check all rays
            if(p.equals(p1)){
                return boundOrVertex;//p is an vertex
            }

            p2 = pts.get(i % N);//right vertex
            if(p.x < Math.min(p1.x, p2.x) || p.x > Math.max(p1.x, p2.x)){//ray is outside of our interests
                p1 = p2;
                continue;//next ray left point
            }

            if(p.x > Math.min(p1.x, p2.x) && p.x < Math.max(p1.x, p2.x)){//ray is crossing over by the algorithm (common part of)
                if(p.y <= Math.max(p1.y, p2.y)){//x is before of ray
                    if(p1.x == p2.x && p.y >= Math.min(p1.y, p2.y)){//overlies on a horizontal ray
                        return boundOrVertex;
                    }

                    if(p1.y == p2.y){//ray is vertical
                        if(p1.y == p.y){//overlies on a vertical ray
                            return boundOrVertex;
                        }else{//before ray
                            ++intersectCount;
                        }
                    }else{//cross point on the left side
                        double xinters = (NumberUtils.sub(p.x , p1.x)) * (NumberUtils.sub(p2.y , p1.y)) / (NumberUtils.sub(p2.x , p1.x)) + p1.y;//cross point of y
                        if(Math.abs(p.y - xinters) < precision){//overlies on a ray
                            return boundOrVertex;
                        }

                        if(p.y < xinters){//before ray
                            ++intersectCount;
                        }
                    }
                }
            }else{//special case when ray is crossing through the vertex
                if(p.x == p2.x && p.y <= p2.y){//p crossing over p2
                    Point2D.Double p3 = pts.get((i+1) % N); //next vertex
                    if(p.x >= Math.min(p1.x, p3.x) && p.x <= Math.max(p1.x, p3.x)){//p.x lies between p1.x & p3.x
                        ++intersectCount;
                    }else{
                        intersectCount += 2;
                    }
                }
            }
            p1 = p2;//next ray left point
        }

        if(intersectCount % 2 == 0){//偶數在多邊形外
            return false;
        } else { //奇數在多邊形內
            return true;
        }

    }
}