# Saving non-orthogonal volume in Nifti format

**URL:** https://discourse.itk.org/t/saving-non-orthogonal-volume-in-nifti-format/2760
**Category:** Engineering
**Created:** [February 25, 2020, 4:12am UTC](https://discourse.itk.org/t/saving-non-orthogonal-volume-in-nifti-format/2760 "2020-02-25T04:12:29Z")
**Posts on this page:** 1
**Showing post:** 21

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### Author: ![lassoan](https://discourse.itk.org/user_avatar/discourse.itk.org/lassoan/32/27_2.png) [@lassoan](https://discourse.itk.org/u/lassoan)
#### Post date: [March 3, 2020, 12:27pm UTC](https://discourse.itk.org/t/saving-non-orthogonal-volume-in-nifti-format/2760/21 "2020-03-03T12:27:36Z")

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As the equation above illustrates, DICOM only specifies image plane I and J axis directions. Applications often define a third (K) axis. For a single plane, you can always choose this K axis direction so that IJK axes form an orthogonal basis. However, you do not have the freedom of choosing arbitrary K axis direction if you want to describe geometry of a gantry-tilt multi-slice volume with a single 4x4 matrix. See for example this [FAQ](http://gdcm.sourceforge.net/wiki/index.php/Gantry_Tilt) and [computation of the shear matrix](https://github.com/rordenlab/dcm2niix/blob/f54be46667fce7994d2062e2623d12253c1bd968/console/nii_dicom_batch.cpp#L4905-L4928).

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