at.addColumn(VisualItem.POLYGON, float[].class);
at.addColumn("id", int.class);
// add nodes to aggregates
// create an aggregate for each 3-clique of nodes
Iterator nodes = vg.nodes();
for ( int i=0; i<3; ++i ) {
AggregateItem aitem = (AggregateItem)at.addItem();
aitem.setInt("id", i);
for ( int j=0; j<3; ++j ) {
aitem.addItem((VisualItem)nodes.next());