Check if lat/long point is inside polygons

Question

**Hi , I need help to Check if  array of lat/long point is inside polygons in map.**

Answer 1

Hello,​

Welcome to our Microsoft Q&A platform!

Xamarin.Forms.Maps do not have this API to check the point is inside polygons, but we can judge it by ourselves. I refer to this thread, then I change it get following answer.

   public bool IsPointInPolygon(Position p, Position[] polygon)  
           {  
               double minX = polygon[0].Latitude;  
               double maxX = polygon[0].Latitude;  
               double minY = polygon[0].Longitude;  
               double maxY = polygon[0].Longitude;  
               for (int i = 1; i < polygon.Length; i++)  
               {  
                   Position q = polygon[i];  
                   minX = Math.Min(q.Latitude, minX);  
                   maxX = Math.Max(q.Latitude, maxX);  
                   minY = Math.Min(q.Longitude, minY);  
                   maxY = Math.Max(q.Longitude, maxY);  
               }  
     
               if (p.Latitude < minX || p.Latitude > maxX || p.Longitude < minY || p.Longitude > maxY)  
               {  
                   return false;  
               }  
     
               // https://wrf.ecse.rpi.edu/Research/Short_Notes/pnpoly.html  
               bool inside = false;  
               for (int i = 0, j = polygon.Length - 1; i < polygon.Length; j = i++)  
               {  
                   if ((polygon[i].Longitude > p.Longitude) != (polygon[j].Longitude > p.Longitude) &&  
                        p.Latitude < (polygon[j].Latitude - polygon[i].Latitude) * (p.Longitude - polygon[i].Longitude) / (polygon[j].Longitude - polygon[i].Longitude) + polygon[i].Latitude)  
                   {  
                       inside = !inside;  
                   }  
               }  
     
               return inside;  
           }  

Best Regards,

Leon Lu

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