public void geometricOverlayUpdate(AnnoListItem item, AnnoScheme.TYPE type, int pos = -1)
        {
            WriteableBitmap overlay = null;

            IMedia video = mediaList.GetFirstVideo();

            if (video != null)
            {
                overlay = video.GetOverlay();
            }
            else
            {
                return;
            }

            overlay.Lock();
            overlay.Clear();

            switch (type)
            {
            case AnnoScheme.TYPE.POINT:
                foreach (PointListItem p in item.Points)
                {
                    if (p.XCoord != -1 && p.YCoord != -1)
                    {
                        Color color = item.Color;
                        //color.A = 128;
                        overlay.FillEllipseCentered((int)p.XCoord, (int)p.YCoord, 1, 1, color);
                    }
                }
                break;

            case AnnoScheme.TYPE.POLYGON:
                break;

            case AnnoScheme.TYPE.GRAPH:
                break;

            case AnnoScheme.TYPE.SEGMENTATION:
                break;
            }

            overlay.Unlock();
        }