public CreatingLineInformation(VisualUnit first, VisualUnit last)
        {
            FirstUnit = first;
            LastUnit  = last;
            Drawing   = new DrawingVisual();

            FirstUnit.PositionChanged += UnitPositionChanged;
            LastUnit.PositionChanged  += UnitPositionChanged;
        }
 public CreatingLineInformation(VisualUnit first) : this(first, new VisualThumb(first.Position))
 {
 }