static bool IsPointInPolygon(Geo x, Geo center, IList<Geo> poly)
{
// do this only once and pass it in for the math.
// Geo c = Limits.center(poly);
// bail out if the point is more than 90 degrees off the
// centroid
var d = x.DistanceRadians(center);
if (d >= (Math.PI / 2))
{
return false;
}
// ray is normal to the great circle from c to x. reusing c to hold ray
// info
var ray = center.CrossNormalize(x);
/*
* side is a point on the great circle between c and x. It is used to
* choose a direction.
*/
var side = x.CrossNormalize(ray);
var isIn = false;
// Why do we need to allocate new Geos?
// Geo p1 = new Geo(poly[0]);
// Geo p2 = new Geo(poly[0]);
var p1 = new Geo(poly[0]);
Geo p2;
var polySize = poly.Count;
for (var i = 1; i < polySize; i++)
{
p2 = new Geo(poly[i]);
/*
* p1 and p2 are on different sides of the ray, and the great acircle
* between p1 and p2 is on the side that counts;
*/
if ((p1.Dot(ray) < 0.0) != (p2.Dot(ray) < 0.0) && new GeoSegment(p1, p2).GreatCircleIntersection(ray).Dot(side) > 0.0)
{
isIn = !isIn;
}
p1 = new Geo(p2);
}
// Check for unclosed polygons, if the polygon isn't closed,
// do the calculation for the last point to the starting
// point.
if (!poly[0].Equals(p1))
{
p2 = new Geo(poly[0]);
if ((p1.Dot(ray) < 0.0) != (p2.Dot(ray) < 0.0) && new GeoSegment(p1, p2).GreatCircleIntersection(ray).Dot(side) > 0.0)
{
isIn = !isIn;
}
}
return isIn;
}
/// <summary>
/// Treating the passed in GeoSegments as planar vectors, return the dot product
/// </summary>
/// <param name="segment1"></param>
/// <param name="segment2"></param>
/// <returns></returns>
public static double Dot(this GeoSegment segment1, GeoSegment segment2)
{
// Using Geo only for convenience, these are NOT Geos, really!
// X is delta longitude, Y is delta latitude, Z is always zero.
var vec1 = new Geo(segment1[1].Longitude - segment1[0].Longitude, segment1[1].Latitude - segment1[0].Latitude, 0).Normalized;
var vec2 = new Geo(segment2[1].Longitude - segment2[0].Longitude, segment2[1].Latitude - segment2[0].Latitude, 0).Normalized;
return vec1.Dot(vec2);
}
