GIS基本算法--03计算点到直线段的最短距离

Author: OrdinarySK

src/algo/MinPointToPolyline.java

@@ -0,0 +1,61 @@
+package algo;
+
+/**
+ * @ClassName MinPointToPolyline
+ * @Description 判断点到线段的最短距离
+ * @Author luokai
+ * @CreateDate 2020/8/16 21:57
+ * @UPpdateUser luokai
+ * @UpdateDate 2020/8/16 21:57
+ * @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;
+
+/***
+ * 原理分析
+ * 点到线段的最短距离  分为三种情况  a.点q的投影点在p1和p2的中间 b.点q的投影点在p1和p2的延长线p2端 c.点q的投影点在p1和p2延长线的p1端
+ *           ---- ----
+ *          (p1q  p1p2)
+ *   r =  ---------------------
+ *           ---- ----
+ *          |p1p2||p1p2|
+ *
+ *          ----
+ *          p1p2    为p1p2的向量
+ *
+ *   c为垂足
+ *    distance   = { |qc|,      0<r<1; }
+ *                { |qp2|,     r>=1; }
+ *                { |qp1|,     r<=0; }
+ *
+ */
+public class MinPointToPolyline {
+
+    public double MinPointToPolyline(Point p1, Point p2, Point q){
+        //两线段的向量点乘
+        double r = (p1.getLon() - q.getLon()) * (p1.getLat() - q.getLat()) + (p2.getLon() - p1.getLon()) * (p2.getLat() - p1.getLat());
+        //d 为p1p2模的平方
+        double d = (p2.getLon() - p1.getLon()) * (p2.getLon() - p1.getLon()) + (p2.getLat() - p1.getLat()) * (p2.getLat() - p1.getLat());
+        double distance ;
+        if(r <= 0){
+            //qp1
+            distance = Math.sqrt((p1.getLon() - q.getLon()) * (p1.getLon() - q.getLon()) + (p1.getLat() - q.getLat()) * (p1.getLat() -q.getLat()));
+        }else if(r >= d){
+            //qp2
+            distance = Math.sqrt((p2.getLon() - q.getLon()) * (p2.getLon() - q.getLon()) + (p2.getLat() - q.getLat()) * (p2.getLat() -q.getLat()));
+        }else{
+            //利用点到直线的公式   cx和cy为垂足点的xy坐标
+            double ra = r / d;
+            double cx = p1.getLon() + (p2.getLon() - p1.getLon()) * ra;
+            double cy = p1.getLat() + (p2.getLat() - p1.getLat()) * ra;
+            distance = Math.sqrt((q.getLon() - cx) * (q.getLon() - cx) + (q.getLat() - cy) * (q.getLat() - cy));
+        }
+
+        return distance;
+    }
+
+}