code: public void _updateXYImpl(boolean bExact) {
  		m_envelope.setEmpty();
  		AttributeStreamOfDbl stream = (AttributeStreamOfDbl) m_vertexAttributes[0];
  		Point2D pt = new Point2D();
  		for (int i = 0; i < m_pointCount; i++) {
  			stream.read(2 * i, pt);
  			m_envelope.merge(pt);
  		}
  	}
docs: \internal Updates x, y intervals.