Determine if a list of points are in clockwise order

[sonomirco]

https://stackoverflow.com/questions/1165647/how-to-determine-if-a-list-of-polygon-points-are-in-clockwise-order.

public static bool IsClockwise(IList<Point3> points)
{

    double sum = 0;

    for (int i = 0; i < points.Count - 1; i++)
    {

        sum += (points[i + 1].X - points[i].X) * (points[i + 1].Y + points[i].Y);

    if (sum == 0.0)
    {
        throw new ArgumentException("The points are on a straight line or are creating a closed loop.");
    }

    return sum > 0;
}

public static bool IsClockwise(IList<Point3> points, Plane pl)
{
    var projectedPts = points.Select(pt => pl.ClosestPoint(pt, out _)).ToList();
    return IsClockwise(projectedPts);
}