_book.createDrawingGroup();
_sheet.aggregateDrawingRecords(_book.getDrawingManager(), true);
EscherAggregate agg = (EscherAggregate) _sheet.findFirstRecordBySid(EscherAggregate.sid);
HSSFPatriarch patriarch = new HSSFPatriarch(this, agg);
agg.clear(); // Initially the behaviour will be to clear out any existing shapes in the sheet when
// creating a new patriarch.
agg.setPatriarch(patriarch);
return patriarch;
}