 chart for vertex labels
				var graphConvertValueToString = graph.convertValueToString;
				graph.convertValueToString = function(cell)
				{
					if (this.model.isVertex(cell))
					{
						var node = document.createElement('canvas');
						node.setAttribute('width', cell.geometry.width);
						node.setAttribute('height', cell.geometry.height);
						
						// Document for empty output if not in DOM
						document.body.appendChild(node);
						
						var ctx = node.getContext("2d");
						new Chart(ctx, c