using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Windows.Forms;

using System.Text;

using Autodesk.Navisworks.Api.Controls;

      static public Point3D GetCentrePointOfSelection()
      {
         Point3D centreOfBox = null;

         //check that selection is valid
         if (!Autodesk.Navisworks.Api.Application.ActiveDocument.CurrentSelection.IsEmpty)
         {
            //Get bounding box of the selection
            BoundingBox3D bb3d =
               Autodesk.Navisworks.Api.Application.ActiveDocument.CurrentSelection.SelectedItems.BoundingBox();

            //get the centre point
            centreOfBox = bb3d.Center;
         }

         //return the vector
         return centreOfBox;
      }