# How does 3D Slicer coordinates work?

**URL:** <https://discourse.slicer.org/t/how-does-3d-slicer-coordinates-work/7519>\
**Category:** Support\
**Created:** [July 11, 2019, 3:39am UTC](https://discourse.slicer.org/t/how-does-3d-slicer-coordinates-work/7519 "2019-07-11T03:39:36Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![pmaquino](https://avatars.discourse-cdn.com/v4/letter/p/7993a0/32.png) [@pmaquino](https://discourse.slicer.org/u/pmaquino)\
**Post date:** [July 11, 2019, 3:39am UTC](https://discourse.slicer.org/t/how-does-3d-slicer-coordinates-work/7519/1 "2019-07-11T03:39:36Z")

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I have two 3D images. One image is much bigger because the other image is cropped from the bigger image. Let’s say I random crop a 50x50x50 image from the 100x100x100. How would I be able to know the coordinates of the smaller image (inside the bigger image) using python when I import both of those?

I tried using the RAS method but it seems that the coordinates I am getting are wrong.

Thank you!

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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:** [July 11, 2019, 3:04pm UTC](https://discourse.slicer.org/t/how-does-3d-slicer-coordinates-work/7519/2 "2019-07-11T15:04:43Z")

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