GIS基本算法--02判断折线段的第二段的拐向

Author: OrdinarySK

src/algo/PolylineDirection.java

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+package algo;
+
+/**
+ * @ClassName PolylineDirection
+ * @Description 判断折线的方向
+ * @Author luokai
+ * @CreateDate 2020/8/16 17:37
+ * @UPpdateUser luokai
+ * @UpdateDate 2020/8/16 17:37
+ * @UpdateRemark
+ * @Version 1.0
+ * Copyright (c) 2019,武汉中地云申科技有限公司
+ * All rights reserved.
+ **/
+
+import entity.Point;
+
+/**
+ * 折线段的拐向判断方法可以直接由矢量叉积的性质推出。对于有公共端点的线段p0p1和p1p2，通过计算(p2 - p0)× (p1 - p0)的符号便可以确定折线段的拐向：
+ * 若(p2 - p0)× (p1 - p0) > 0,则p0p1在p1点拐向右侧后得到p1p2。
+ * 若(p2 - p0)× (p1 - p0) < 0,则p0p1在p1点拐向左侧后得到p1p2。
+ * 若(p2 - p0)× (p1 - p0) = 0,则p0、p1、p2三点共线
+ * 左侧 右侧是指 相对于po---p1方向
+ */
+public class PolylineDirection {
+    private final String right = "右拐";
+    private final String left = "左拐";
+    private final String line = "共线";
+
+    public String PolylineDirection(Point p0, Point p1, Point p2){
+
+        String location = null;
+        if((p2.getLon() - p0.getLon()) * (p1.getLat() - p0.getLat()) - (p2.getLat() - p0.getLat()) * (p1.getLon() - p0.getLon()) > 0){
+            location = right;
+        }else if((p2.getLon() - p0.getLon()) * (p1.getLat() - p0.getLat()) - (p2.getLat() - p0.getLat()) * (p1.getLon() - p0.getLon()) < 0){
+            location = left;
+        }else if((p2.getLon() - p0.getLon()) * (p1.getLat() - p0.getLat()) - (p2.getLat() - p0.getLat()) * (p1.getLon() - p0.getLon()) == 0){
+            location = line;
+        }
+        return location;
+    }
+
+}

src/test/Test02.java

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+package test;
+
+import algo.PolylineDirection;
+import entity.Point;
+
+/**
+ * @ClassName Test02
+ * @Description TODO
+ * @Author luokai
+ * @CreateDate 2020/8/16 18:11
+ * @UPpdateUser luokai
+ * @UpdateDate 2020/8/16 18:11
+ * @UpdateRemark
+ * @Version 1.0
+ * Copyright (c) 2019,武汉中地云申科技有限公司
+ * All rights reserved.
+ **/
+public class Test02 {
+    public static void main(String args[]){
+        Point p0 = new Point(10,20);
+        Point p1 = new Point(12,20);
+        Point p2 = new Point(15,30);
+
+        PolylineDirection polylineDirection = new PolylineDirection();
+        String text = polylineDirection.PolylineDirection(p0, p1, p2);
+        System.out.println(text);
+    }
+
+}