# Computing and accessing normals from cells instead of points

**URL:** https://discourse.slicer.org/t/computing-and-accessing-normals-from-cells-instead-of-points/20174
**Category:** Support
**Tags:** python
**Created:** [October 15, 2021, 3:25pm UTC](https://discourse.slicer.org/t/computing-and-accessing-normals-from-cells-instead-of-points/20174 "2021-10-15T15:25:29Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![adamy](https://avatars.discourse-cdn.com/v4/letter/a/a88e57/32.png) [@adamy](https://discourse.slicer.org/u/adamy)
#### Post date: [October 15, 2021, 3:25pm UTC](https://discourse.slicer.org/t/computing-and-accessing-normals-from-cells-instead-of-points/20174/1 "2021-10-15T15:25:29Z")

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Hi all, I am very new to using Slicer. I would like to generate normals for each cell instead of the default point normals.

I have been able to set the cell normals flag on (and the point cell normals flag off) in the python interactor using `vtk.vtkPolyDataNormals().ComputeCellNormalsOn()` however I am not sure how to actually generate an array of normals after the flags have been set. Using `getNode("Output Volume").GetPolyData().GetCellData().GetArray("Normals")` yields nothing.

Any suggestions on how to generate and access cell normals?