public void Add(CurveGraphModel model)
        {
            if (Items != null)
            {
                Items.Clear();
                modelitems = null;
            }
            else
            {
                Items      = new ObservableCollection <FrameworkElement>();
                modelitems = new CurveGraphModel();
            }

            modelitems = model;

            GraphGrid grid = DrawGrid.RenderGrid(model, camera);

            model.Item.Grid = grid;

            if (UpdateRender != null)
            {
                UpdateRender(this, EventArgs.Empty);
            }
        }