class_docstr: 3D image from a single, supports resampling and reorientation
  (3D image from a set of 2D slices is currently not supported).
class_docstr_tok: ["3D","image","from","a","single",",","supports","resampling","and","reorientation","(","3D","image","from","a","set","of","2D","slices","is","currently","not","supported",")","."]
code: def output_pixdim(self):
      if self._output_pixdim is None:
          self.output_pixdim = None
      return tuple(self._output_pixdim)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  from abc import ABCMeta, abstractmethod
  import nibabel
  import numpy
  import tensorflow
  from six import with_metaclass, string_types
  import niftynet.io.misc_io
  from niftynet.io.image_loader import load_image_obj
  from niftynet.io.misc_io import resolve_file_name, dtype_casting
  from niftynet.utilities.niftynet_global_config import NiftyNetGlobalConfig
label_desc: Use image node_id 2 for calling the SpatialImage3D obj's underlying member method code with example usage: obj.output_pixdim() and returns: tuple