# How to convert xyz to RAS

**URL:** <https://discourse.slicer.org/t/how-to-convert-xyz-to-ras/42688>\
**Category:** Support\
**Tags:** dicom\
**Created:** [April 25, 2025, 4:06pm UTC](https://discourse.slicer.org/t/how-to-convert-xyz-to-ras/42688 "2025-04-25T16:06:59Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![zxy630](https://avatars.discourse-cdn.com/v4/letter/z/e480ec/32.png) [@zxy630](https://discourse.slicer.org/u/zxy630)\
**Post date:** [April 25, 2025, 4:06pm UTC](https://discourse.slicer.org/t/how-to-convert-xyz-to-ras/42688/1 "2025-04-25T16:06:59Z")

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I have an xyz coordinate of 31.4, -39.6, -216.4, but the corresponding RAS coordinates are -34.88, 38.816, -204.997. I find that there are deviations in the coordinates when importing. This is not just a simple relationship of reversing the xy axes. Could anyone please tell me what the cause is and how to solve it?  
My dicom’s detail is as follows:

 ![detail](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/2/2/22bfc5d8a81b023b0c21346b6f43aedb21eba614.png)

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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:** [April 25, 2025, 4:07pm UTC](https://discourse.slicer.org/t/how-to-convert-xyz-to-ras/42688/2 "2025-04-25T16:07:51Z")

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What coordinate system do you refer to as XYZ? What are the origin, spacing, and axis directions?

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**Author:** ![zxy630](https://avatars.discourse-cdn.com/v4/letter/z/e480ec/32.png) [@zxy630](https://discourse.slicer.org/u/zxy630)\
**Post date:** [April 26, 2025, 2:54am UTC](https://discourse.slicer.org/t/how-to-convert-xyz-to-ras/42688/3 "2025-04-26T02:54:55Z")

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Actually, i don’t know the origin coordinate system. I only know the coordinate is from FluoroCT, and we want to import the mark to 3Dslicer now. The spacing is [0.43, 0. 43, 0.625]. The origin is [78.132, 153.069, -275.262]. Can you give me some advice?

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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:** [April 26, 2025, 12:25pm UTC](https://discourse.slicer.org/t/how-to-convert-xyz-to-ras/42688/4 "2025-04-26T12:25:17Z")

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Assuming that by “FluoroCT” you mean CBCT reconstruction by a fluoro (C-arm) that is saved in DICOM, the coordinates are in LPS coordinate system. You can convert between LPS and RAS coordinate systems by inverting the sign of the first two coordinates.