# Find Pixel Coordinates of 3D Volume (DICOM) Before and After Multi-planar Reformatting (MPR) with vtkImageReslice

**URL:** https://discourse.vtk.org/t/find-pixel-coordinates-of-3d-volume-dicom-before-and-after-multi-planar-reformatting-mpr-with-vtkimagereslice/1872
**Category:** Support
**Created:** [October 4, 2019, 8:41pm UTC](https://discourse.vtk.org/t/find-pixel-coordinates-of-3d-volume-dicom-before-and-after-multi-planar-reformatting-mpr-with-vtkimagereslice/1872 "2019-10-04T20:41:29Z")
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### Author: ![lassoan](https://discourse.vtk.org/user_avatar/discourse.vtk.org/lassoan/32/50_2.png) [@lassoan](https://discourse.vtk.org/u/lassoan)
#### Post date: [October 5, 2019, 3:08am UTC](https://discourse.vtk.org/t/find-pixel-coordinates-of-3d-volume-dicom-before-and-after-multi-planar-reformatting-mpr-with-vtkimagereslice/1872/2 "2019-10-05T03:08:16Z")

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What works for us every time for solving such problems, without any trial and error, is the following process:

- Define all coordinate systems in your application: a short unique name, origin, axes unit, and axes directions. You can describe these in a table and it usually helps if you draw a sketch. See an example [here](http://perk-software.cs.queensu.ca/plus/doc/nightly/user/ApplicationfCalCoordinateSystemDefinitions.html). Your coordinate systems will be something like: InputVolumeIJK, InputVolumeLPS, AlignedVolumeLPS, SliceView.
- Name all your transforms consistently, as transforms between two coordinate systems (e.g., AtoBTransform). Just by looking at your coordinate system definitions, it should be always simple to determine transformation matrix between two coordinates systems. These pair of transforms will connect all your transforms in a graph.
- You can get transforms between any two coordinate systems by multiplying the transformation matrices that get you from one coordinate system to the other (this is where the sketch that you draw in the first step is particularly useful).

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