# How to understand the SliceToRAS matrix?

**URL:** <https://discourse.slicer.org/t/how-to-understand-the-slicetoras-matrix/10630>\
**Category:** Development\
**Created:** [March 10, 2020, 10:39pm UTC](https://discourse.slicer.org/t/how-to-understand-the-slicetoras-matrix/10630 "2020-03-10T22:39:04Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Illusion](https://avatars.discourse-cdn.com/v4/letter/i/e19b73/32.png) [@Illusion](https://discourse.slicer.org/u/Illusion)\
**Post date:** [March 10, 2020, 10:39pm UTC](https://discourse.slicer.org/t/how-to-understand-the-slicetoras-matrix/10630/1 "2020-03-10T22:39:04Z")

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Hello,

It seems that there are a lot of coordinate systems involved in Slicer. 😀  
I was trying to find a tutorial explaining the different coordinate systems and transformations among each other, however, failed to find a good one.

Specifically,

1. How many Coordinate Systems (CSs) are involved Slicer? (e.g., IJK, XYZ, SliceNode? VolumeNode? RAS? LAS, LPI, RPI…)

2. How are those CSs employed in Slicer? (e.g., what exactly is a coordinate of Slice? and what does the matrix of SliceToRAS do?)

3. Any resource or tutorial that explains how the principles of different transformation matrixes mathematically?

Thank you very much!

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**Author:** ![pieper](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/pieper/32/8_2.png) [@pieper](https://discourse.slicer.org/u/pieper)\
**Post date:** [March 11, 2020, 12:38am UTC](https://discourse.slicer.org/t/how-to-understand-the-slicetoras-matrix/10630/2 "2020-03-11T00:38:39Z")

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Hi -

This is a good place to start: [https://www.slicer.org/wiki/Coordinate\_systems](https://www.slicer.org/wiki/Coordinate_systems)

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**Author:** ![Illusion](https://avatars.discourse-cdn.com/v4/letter/i/e19b73/32.png) [@Illusion](https://discourse.slicer.org/u/Illusion)\
**Post date:** [March 11, 2020, 7:09pm UTC](https://discourse.slicer.org/t/how-to-understand-the-slicetoras-matrix/10630/3 "2020-03-11T19:09:47Z")

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Thank you for providing this link, Pieper!

Yes, that is a good place to start; though it could not answer my questions systematically. 😜