# Extract Surface does not remove internal surfaces

**URL:** https://discourse.paraview.org/t/extract-surface-does-not-remove-internal-surfaces/12552
**Category:** ParaView Support
**Created:** [July 20, 2023, 1:42pm UTC](https://discourse.paraview.org/t/extract-surface-does-not-remove-internal-surfaces/12552 "2023-07-20T13:42:56Z")
**Posts on this page:** 5
**Page:** 1

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### Author: ![Massimiliano\_Leoni](https://discourse.paraview.org/user_avatar/discourse.paraview.org/massimiliano_leoni/32/376_2.png) [@Massimiliano\_Leoni](https://discourse.paraview.org/u/Massimiliano_Leoni)
#### Post date: [July 20, 2023, 1:42pm UTC](https://discourse.paraview.org/t/extract-surface-does-not-remove-internal-surfaces/12552/1 "2023-07-20T13:42:56Z")

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[I originally posted at [https://gitlab.kitware.com/paraview/paraview/-/issues/22185#note\_1378880](https://gitlab.kitware.com/paraview/paraview/-/issues/22185#note_1378880) but I was advised to post here].

I have a file [tried with VTU and Fides] written in parallel [MPI]. When I open it I can see internal surfaces on the borders between the parallel partitions of the mesh. The Extract Surface filter has two options, “Piece Invariant” and “Remove Ghost Interfaces” which from their description more or less sound like they should get rid of the internal surfaces but they actually don’t [nor does any combination of the two].

 ![image](https://discourse.paraview.org/uploads/default/original/2X/d/d9dd62347908de79bbeafd5acb6579495c2eb49a.jpeg)

Is this correct? Am I misunderstanding what these options do?

I tried to use the CleanToGrid and CleanCellsToGrid filters but they didn’t do anything.

I am attaching the file I am using to test this, it’s in Fides BP5 format.  
[uR.bp.zip](https://discourse.paraview.org/uploads/short-url/xha39E4mhkWoAPioKWrtF0HbJQ1.zip) (106.7 KB)

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### Author: ![nicolas.vuaille](https://discourse.paraview.org/user_avatar/discourse.paraview.org/nicolas.vuaille/32/5873_2.png) [@nicolas.vuaille](https://discourse.paraview.org/u/nicolas.vuaille)
#### Post date: [July 20, 2023, 2:49pm UTC](https://discourse.paraview.org/t/extract-surface-does-not-remove-internal-surfaces/12552/2 "2023-07-20T14:49:29Z")

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Did you try the `GhostCellsGenerator` before the `Extract Surface` ?

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### Author: ![Massimiliano\_Leoni](https://discourse.paraview.org/user_avatar/discourse.paraview.org/massimiliano_leoni/32/376_2.png) [@Massimiliano\_Leoni](https://discourse.paraview.org/u/Massimiliano_Leoni)
#### Post date: [July 21, 2023, 8:43am UTC](https://discourse.paraview.org/t/extract-surface-does-not-remove-internal-surfaces/12552/3 "2023-07-21T08:43:37Z")

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I tried it just now and unfortunately it didn’t change anything ☹

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### Author: ![nicolas.vuaille](https://discourse.paraview.org/user_avatar/discourse.paraview.org/nicolas.vuaille/32/5873_2.png) [@nicolas.vuaille](https://discourse.paraview.org/u/nicolas.vuaille)
#### Post date: [July 21, 2023, 9:24am UTC](https://discourse.paraview.org/t/extract-surface-does-not-remove-internal-surfaces/12552/4 "2023-07-21T09:24:33Z")

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My bad, `GhostCellsGenerator` is only a thing if you are running a `pvserver` with MPI.

Can you share the `vtu` file ? Fides is not enabled by default in ParaView

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### Author: ![Massimiliano\_Leoni](https://discourse.paraview.org/user_avatar/discourse.paraview.org/massimiliano_leoni/32/376_2.png) [@Massimiliano\_Leoni](https://discourse.paraview.org/u/Massimiliano_Leoni)
#### Post date: [July 21, 2023, 10:10am UTC](https://discourse.paraview.org/t/extract-surface-does-not-remove-internal-surfaces/12552/5 "2023-07-21T10:10:47Z")

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Sure, here comes!  
[uR.zip](https://discourse.paraview.org/uploads/short-url/3BAVZaWxMmPzezmHKp6vs82XXCI.zip) (441.1 KB)