protected virtual Size ComputeCellSize()

The CellSize, unless one or both of its width and height are Double.NaN or zero. If that is the case, it uses the width and/or height from the node's Northwoods.GoXam.Part.ResizeCellSize. But if one or both of the width and height are still Double.NaN or zero, it searches for a grid snapping node behind the AdornedNode, one that is Northwoods.GoXam.Part.DragOverSnapEnabled, and uses its Northwoods.GoXam.Part.DragOverSnapCellSize. If it cannot find such a grid snapping node, or one or both of the width and height are NaN, it uses the diagram's Northwoods.GoXam.Diagram.GridSnapCellSize if the diagram is Northwoods.GoXam.Diagram.GridSnapEnabled. Finally, it defaults to 1x1.