# Transformation graph for quick calculation of concatenated transforms

**URL:** <https://discourse.slicer.org/t/transformation-graph-for-quick-calculation-of-concatenated-transforms/326>\
**Category:** Development\
**Created:** [May 16, 2017, 5:23pm UTC](https://discourse.slicer.org/t/transformation-graph-for-quick-calculation-of-concatenated-transforms/326 "2017-05-16T17:23:41Z")\
**Posts on this page:** 1\
**Showing post:** 10

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**Author:** ![xxzhou](https://avatars.discourse-cdn.com/v4/letter/x/13edae/32.png) [@xxzhou](https://discourse.slicer.org/u/xxzhou)\
**Post date:** [September 11, 2018, 3:15pm UTC](https://discourse.slicer.org/t/transformation-graph-for-quick-calculation-of-concatenated-transforms/326/10 "2018-09-11T15:15:30Z")

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Hi! I am new for 3D Slicer, and when I to used your method to calculate the transform matrix, I found that  
a = getNode().GetParentTransformNode,  
a is NONE, same as b. This resulted in transformAToB equaled to Identity Matrix.

But if I directly use  
a,b = getNode(),  
transformAToB = slicer.vtkMRMLTransformNode()  
slicer.vtkMRMLTransformNode.GetTransformBetweenNodes(a, b, transformAToB)

I was told method requires a vtkMRMLTransformNode, a vtkMRMLScalarVolumeNode was provided.

I am wondering if anyone could help me find out why this problem comes out.

Appreciate your help!  
Thank you.  
Cheers,  
xxzhou

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