class_docstr: Provides methods to allow conversion between sheet and matrix
  coordinates.
code: def __get_ydensity(self):
      return self.__ydensity
  
imports: import numpy
  from .boundingregion import BoundingBox
  from .util import datetime_types
label_desc: Use image node_id 2 for calling the SheetCoordinateSystem obj's underlying member method code with example usage: obj.__get_ydensity() and returns: self