How to calculate Convex hull?

[GangHan]

Hi, I want to calucate the convex hull of the point set and get the points of the convex hull polygon. The code is as follows:
public ArrayList ConvexHull(ArrayList pts)
        {
            IGeometryCollection geomCol = null;
            object missing = Type.Missing;
            IPoint geom;

            geom = new PointClass();
            geomCol = new MultipointClass();

            for (int i = 0; i < pts.Count; i++)
            {
                geom.X = ((MyPoint)pts).x;
                geom.Y = ((MyPoint)pts).z;
                geomCol.AddGeometry(geom as IGeometry, ref missing, ref missing);
            }           
           
            ITopologicalOperator topoOP =geomCol as ITopologicalOperator;
            if (!topoOP.IsSimple) topoOP.Simplify();
            IGeometry convexHull = topoOP.ConvexHull();
            IPointCollection ps = (convexHull as IPolygon) as IPointCollection;
            ArrayList c=new ArrayList();
            for (int i = 0; i < ps.PointCount; i++)
            {
                c.Add(ps.get_Point(i));
            }
            return c;
        }
But I didn't get right result. Why? Thank you very much.

[NeilClemmons]

You're adding the same point object over and over.  The For loop is just changing the coordinates of that one point object.

geom = new PointClass();

This should be inside your For loop.

[GangHan]

That's right. Thank you very much.

You're adding the same point object over and over.  The For loop is just changing the coordinates of that one point object.

geom = new PointClass();

This should be inside your For loop.