Question

I saved group of points on my panel to List<MyVector> savedPoints, then I calculated the the point with lowest coordinate y :

 public void searchLowest()  
    {
        MyVector temp;
        double ylon = savedPoints[0].getY();
        for (int i = 0; i < savedPoints.Count; i++)
        {
            if (savedPoints[i].getY() > ylon)
            {
                ylon = savedPoints[i].getY();
                lowest = i;
            }
        }

        temp = savedPoints[lowest];
    }

after this I made a method to calculate polar angles :

public static double angle(MyVector vec1, MyVector vec2) 
        {
            double angle = Math.Atan2(vec1.getY() - vec2.getY(), vec1.getX() - vec2.getX());
            return angle;
        }

now don’t know how to use Gift wrapping algorithm in my case. The pseudocode on WikiPedia link is not really understandable for me, so I’m asking for help here.

I’m using C# and win forms (net.framework 4.0)

Thanks for any help.

Answer 1

Using this as a reference, here is teh code:

namespace GiftWrapping
{
    using System.Drawing;
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;

    class Program
    {
        static void Main(string[] args)
        {
            List<Point> test = new List<Point>(
                new Point[]
                    {
                        new Point(200,200), new Point(300,100), new Point(200,50), new Point(100,100),
                        new Point(200, 100), new Point(300, 200), new Point(250, 100), 
                    });

            foreach (Point point in ConvexHull(test))
            {
                Console.WriteLine(point);
            }

            Console.ReadKey();

        }

        public static List<Point> ConvexHull(List<Point> points)
        {
            if (points.Count < 3)
            {
                throw new ArgumentException("At least 3 points reqired", "points");
            }

            List<Point> hull = new List<Point>();

            // get leftmost point
            Point vPointOnHull = points.Where(p => p.X == points.Min(min => min.X)).First();

            Point vEndpoint;
            do
            {
                hull.Add(vPointOnHull);
                vEndpoint = points[0];

                for (int i = 1; i < points.Count; i++)
                {
                    if ((vPointOnHull == vEndpoint)
                        || (Orientation(vPointOnHull, vEndpoint, points[i]) == -1))
                    {
                        vEndpoint = points[i];
                    }
                }

                vPointOnHull = vEndpoint;

            }
            while (vEndpoint != hull[0]);

            return hull;
        }

        private static int Orientation(Point p1, Point p2, Point p)
        {
            // Determinant
            int Orin = (p2.X - p1.X) * (p.Y - p1.Y) - (p.X - p1.X) * (p2.Y - p1.Y);

            if (Orin > 0)
                return -1; //          (* Orientation is to the left-hand side  *)
            if (Orin < 0)
                return 1; // (* Orientation is to the right-hand side *)

            return 0; //  (* Orientation is neutral aka collinear  *)
        }
    }
}

adaptation to your private classes, would be your homework.