Android的檢查，如果我的緯度/經度位置withing給定區域

Question

假設我有以下的緯度/經度，在地圖上創建區域的多邊形

39.888932, -95.557237 
42.156511, -101.347921 
40.322707, -101.040304 
38.299884, -100.447042 
36.731433, -96.623800 

現在，我怎麼檢查是否40.356203, -97.304952這個緯度/經度爲在該給定區域內還是沒有。

我該怎麼做？

Answer 1

剛剛嘗試識別多邊形中的點的Ray Casting算法。這工作完美。

參考http://en.wikipedia.org/wiki/Point_in_polygon的光線投射

private boolean isPointInPolygon(LatLng tap, ArrayList<LatLng> vertices) { 
     int intersectCount = 0; 
     for (int j = 0; j < vertices.size() - 1; j++) { 
      if (rayCastIntersect(tap, vertices.get(j), vertices.get(j + 1))) { 
       intersectCount++; 
      } 
     } 

     return ((intersectCount % 2) == 1); // odd = inside, even = outside; 
    } 

    private boolean rayCastIntersect(LatLng tap, LatLng vertA, LatLng vertB) { 

     double aY = vertA.latitude; 
     double bY = vertB.latitude; 
     double aX = vertA.longitude; 
     double bX = vertB.longitude; 
     double pY = tap.latitude; 
     double pX = tap.longitude; 

     if ((aY > pY && bY > pY) || (aY < pY && bY < pY) 
       || (aX < pX && bX < pX)) { 
      return false; // a and b can't both be above or below pt.y, and a or 
          // b must be east of pt.x 
     } 

     double m = (aY - bY)/(aX - bX); // Rise over run 
     double bee = (-aX) * m + aY; // y = mx + b 
     double x = (pY - bee)/m; // algebra is neat! 

     return x > pX; 
    }