int num = aggr.getTupleCount();
if ( num == 0 ) return;
// update buffers
int maxsz = 0;
for ( Iterator aggrs = aggr.tuples(); aggrs.hasNext(); )
maxsz = Math.max(maxsz, 4*2*
((AggregateItem)aggrs.next()).getAggregateSize());
if ( m_pts == null || maxsz > m_pts.length ) {
m_pts = new double[maxsz];
}