# Need to convert vtkMRMLScalarVolumeNode and vtkMRMLCommandLineVolumeNode to Numpy Array

**URL:** <https://discourse.slicer.org/t/need-to-convert-vtkmrmlscalarvolumenode-and-vtkmrmlcommandlinevolumenode-to-numpy-array/226>\
**Category:** Support\
**Created:** [April 28, 2017, 9:01pm UTC](https://discourse.slicer.org/t/need-to-convert-vtkmrmlscalarvolumenode-and-vtkmrmlcommandlinevolumenode-to-numpy-array/226 "2017-04-28T21:01:41Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![siddiqueodu](https://avatars.discourse-cdn.com/v4/letter/s/9fc348/32.png) [@siddiqueodu](https://discourse.slicer.org/u/siddiqueodu)\
**Post date:** [April 28, 2017, 9:01pm UTC](https://discourse.slicer.org/t/need-to-convert-vtkmrmlscalarvolumenode-and-vtkmrmlcommandlinevolumenode-to-numpy-array/226/1 "2017-04-28T21:01:41Z")

</div>

I am using slicer module in my own module to get bias corrected volume. The following function is working correctly.

```auto
def biascorrection(volumeNode1):
  parameters = {}
  parameters["inputImageName"] = volumeNode1.GetID()
  outModel = slicer.vtkMRMLScalarVolumeNode()
  slicer.mrmlScene.AddNode(outModel)
  parameters["outputImageName"] = outModel.GetID()
  biascorrect = slicer.modules.n4itkbiasfieldcorrection
  return (slicer.cli.run(biascorrect, None, parameters))

Vol1_biasCorrect = biascorrection(nodet1)

```

Output node is (vtkCommonCorePython.vtkMRMLCommandLineModuleNode)0x7fc11452a808. To get numpy array of this vtk node, I have been used the following code:

```auto
Vol1_biasCorrectNode = slicer.util.getNode('Volume')
Vol1_biasCorrect_array = slicer.util.array(Vol1_biasCorrectNode.GetID())

```

The following error appears:

```auto
File "/home/siddique/Slicer-4.6.2-linux-amd64/bin/Python/slicer/util.py", line 583, in array
    shape = list(n.GetImageData().GetDimensions())
AttributeError: 'NoneType' object has no attribute 'GetDimensions'

```

As output volume is created as `vtkMRMLScalarVolumeNode()`, I think this volume should be converted to numpy array. Please help me to get the numpy array of bias corrected volume.

---

<div class="post-metadata">

**Author:** ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)\
**Post date:** [April 28, 2017, 9:30pm UTC](https://discourse.slicer.org/t/need-to-convert-vtkmrmlscalarvolumenode-and-vtkmrmlcommandlinevolumenode-to-numpy-array/226/2 "2017-04-28T21:30:03Z")

</div>

Specify wait\_for\_completion=True to block execution until the CLI execution is complete. See details here: [https://www.slicer.org/wiki/Documentation/Nightly/Developers/Python\_scripting#Running\_a\_CLI\_from\_Python](https://www.slicer.org/wiki/Documentation/Nightly/Developers/Python_scripting#Running_a_CLI_from_Python)