在某个经纬度附近

1纬度居然有111319.5米

直接判断两个经纬度的距离太麻烦了，于是用了个简单的替代方案

根据距离算单位经纬度，在两个经度和两个纬度之间的就算是附近

public const double DeltLat = 1 / 111319.5;

public static double DeltLong(double lat)
{
    return DeltLat / Math.Cos(lat * Math.PI / 180);
}

public static bool IsNearby(double aOriginalLat, double aOriginalLong, double aLat, double aLong, double aDistence)
{
    var degreeLat = aDistence * DeltLat;
    var degreeLong = aDistence * DeltLong(aOriginalLat);
    return aLat < aOriginalLat + degreeLat && aLat > aOriginalLat - degreeLat &&
           aLong < aOriginalLong + degreeLong && aLong > aOriginalLong - degreeLong;
}