public override string ToString()
{
BitStream bits = new BitStream();
StringBuilder sb = new StringBuilder();
sb.Append( "RECT " );
sb.AppendFormat( "{0:d}Bits/entry, ", bits.CountMaximumBits( _x_min, _x_max, _y_min, _y_max ) );
sb.AppendFormat( "Xmin {0:d} / Xmax {1:d} / Ymin {2:d} / Ymax {3:d}",
_x_min, _x_max, _y_min, _y_max );
return sb.ToString();
}