Geo Fencing - point inside/outside polygon

Question

I would like to determine a polygon and implement an algorithm which would check if a point is inside or outside the polygon.

Does anyone know if there is any example available of any similar algorithm?

Answer 1

If i remember correctly, the algorithm is to draw a horizontal line through your test point. Count how many lines of of the polygon you intersect to reach your point.

If the answer is odd, you're inside. If the answer is even, you're outside.

Edit: Yeah, what he said (Wikipedia):

Answer 2

C# code

bool IsPointInPolygon(List<Loc> poly, Loc point) {     int i, j;     bool c = false;     for (i = 0, j = poly.Count - 1; i < poly.Count; j = i++)     {         if ((((poly[i].Lt <= point.Lt) && (point.Lt < poly[j].Lt))                  || ((poly[j].Lt <= point.Lt) && (point.Lt < poly[i].Lt)))                  && (point.Lg < (poly[j].Lg - poly[i].Lg) * (point.Lt - poly[i].Lt)                      / (poly[j].Lt - poly[i].Lt) + poly[i].Lg))         {              c = !c;         }     }      return c; } 

Location class

public class Loc {     private double lt;     private double lg;      public double Lg     {         get { return lg; }         set { lg = value; }     }      public double Lt     {         get { return lt; }         set { lt = value; }     }      public Loc(double lt, double lg)     {         this.lt = lt;         this.lg = lg;     } }