Calculates the convex hull from a given list of Revit points

ConvexHull.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Autodesk.Revit.DB;


namespace Geometry
{
  / /// <summary>
  /// Adapted from http://en.wikibooks.org/wiki/Algorithm_Implementation/Geometry/Convex_hull/Monotone_chain
  /// </summary>
  public static class ConvexHull
  {
    private static double cross(XYZ O, XYZ A, XYZ B)
    {
      return (A.X - O.X) * (B.Y - O.Y) - (A.Y - O.Y) * (B.X - O.X);
    }
    public static List<XYZ> CalcConvexHull(List<XYZ> points)
    {
      points.OrderBy(p => p.X).ThenBy(p => p.Y);

      var lower = new List<XYZ>();
      for (var i = 0; i < points.Count; i++)
      {
        while (lower.Count >= 2 && cross(lower[lower.Count - 2], lower[lower.Count - 1], points[i]) <= 0)
        {
          lower.RemoveAt(lower.Count - 1);
        }
        lower.Add(points[i]);
      }

      var upper = new List<XYZ>();
      for (var i = points.Count - 1; i >= 0; i--)
      {
        while (upper.Count >= 2 && cross(upper[upper.Count - 2], upper[upper.Count - 1], points[i]) <= 0)
        {
          upper.RemoveAt(upper.Count - 1);
        }
        upper.Add(points[i]);
      }

      upper.RemoveAt(upper.Count - 1);
      lower.RemoveAt(lower.Count - 1);
      return lower.Concat(upper).ToList();
    }
  }
}