GpsCardGatewayPosition/GpsCardGatewayPosition.Common/Helper/ChinaPolygon.cs

using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace GpsCardGatewayPosition.Common.Helper
{
    public class ChinaPolygon
    {
        private static readonly PolyGon China;
        private const string ChinaStr = 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        static ChinaPolygon()
        {
            China = JsonConvert.DeserializeObject<PolyGon>(ChinaStr);
        }

        public static bool IsInChina(double lat, double lng)
        {
            return China.FindPoint(lat, lng);
        }
        /// <summary>
        /// 
        /// </summary>
        private class Point
        {
            public double X { get; set; } = 0;
            public double Y { get; set; } = 0;
        }
        /// <summary>
        /// 
        /// </summary>
        private class PolyGon
        {
            public List<Point> myPts = new List<Point>();
            public PolyGon()
            {
            }
            public PolyGon(List<Point> points)
            {
                foreach (Point p in points)
                {
                    myPts.Add(p);
                }
            }
            public void Add(Point p)
            {
                myPts.Add(p);
            }

            private int Count()
            {
                return myPts.Count;
            }


            //  The function will return true if the point x,y is inside the polygon, or
            //  false if it is not.  If the point is exactly on the edge of the polygon,
            //  then the function may return true or false.

            public bool FindPoint(double X, double Y)
            {
                int sides = Count() - 1;
                int j = sides - 1;
                bool pointStatus = false;
                for (int i = 0; i < sides; i++)
                {
                    if (myPts[i].Y < Y && myPts[j].Y >= Y || myPts[j].Y < Y && myPts[i].Y >= Y)
                    {
                        if (myPts[i].X + (Y - myPts[i].Y) / (myPts[j].Y - myPts[i].Y) * (myPts[j].X - myPts[i].X) < X)
                        {
                            pointStatus = !pointStatus;
                        }
                    }
                    j = i;
                }
                return pointStatus;
            }
        }
    }
}