# Q-criterion calculation for cell-based .pvtu files

**URL:** https://discourse.paraview.org/t/q-criterion-calculation-for-cell-based-pvtu-files/15742
**Category:** ParaView Support
**Created:** [November 19, 2024, 6:14am UTC](https://discourse.paraview.org/t/q-criterion-calculation-for-cell-based-pvtu-files/15742 "2024-11-19T06:14:02Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![CFDER-HF](https://discourse.paraview.org/user_avatar/discourse.paraview.org/cfder-hf/32/15557_2.png) [@CFDER-HF](https://discourse.paraview.org/u/CFDER-HF)
#### Post date: [November 19, 2024, 6:14am UTC](https://discourse.paraview.org/t/q-criterion-calculation-for-cell-based-pvtu-files/15742/1 "2024-11-19T06:14:03Z")

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Dear all,  
I am attempting to calculate the Q-criterion for my cell-based data stored in a `.pvtu` file along with its associated `.vtu` files. After converting the cell-based data to point data, I used the ‘Gradient’ filter on the velocity vector to compute the Q-criterion. However, the resulting values are globally zero, which appears to be caused by a mismatch between the point data and the corresponding coordinates.  
Any insights or suggestions would be greatly appreciated!  
Best regards,  
Y.X.Wang

 ![image](https://discourse.paraview.org/uploads/default/original/2X/3/35224888482b4add87f9f511b48aa8260a67d8a3.jpeg)  
The case is flow over a 3D cylinder, and the above is the U distribution  
 ![image](https://discourse.paraview.org/uploads/default/original/2X/f/fc4c14c5ac3dd34e33495d67d995b43515327d55.jpeg)  
This is the result of Q-criterion calculation