# Npy transform matrix

**URL:** <https://discourse.slicer.org/t/npy-transform-matrix/18152>\
**Category:** Support\
**Tags:** registration, python\
**Created:** [June 15, 2021, 9:25pm UTC](https://discourse.slicer.org/t/npy-transform-matrix/18152 "2021-06-15T21:25:07Z")\
**Posts on this page:** 1\
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**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:** [June 16, 2021, 5:35pm UTC](https://discourse.slicer.org/t/npy-transform-matrix/18152/2 "2021-06-16T17:35:49Z")

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Slicer uses all data in LPS coordinate system in files (following conventions set by DICOM, ITK, and most other modern medical image computing software), while uses RAS in the scene (for backward compatibility). You need to apply LPS\<-\>RAS basis transform if you import an LPS transform as shown [here](https://slicer.readthedocs.io/en/latest/developer_guide/script_repository.html#convert-between-itk-and-slicer-linear-transforms). You also need to be aware of the transform direction (modeling/resampling; from/to parent).

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