# Contour Filter vs ISO Volume filter

**URL:** https://discourse.paraview.org/t/contour-filter-vs-iso-volume-filter/12355
**Category:** ParaView Support
**Created:** [June 21, 2023, 2:01pm UTC](https://discourse.paraview.org/t/contour-filter-vs-iso-volume-filter/12355 "2023-06-21T14:01:40Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![phismith](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/p/a9adbd/32.png) [@phismith](https://discourse.paraview.org/u/phismith)
#### Post date: [June 21, 2023, 2:01pm UTC](https://discourse.paraview.org/t/contour-filter-vs-iso-volume-filter/12355/1 "2023-06-21T14:01:40Z")

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Hello,  
I was wondering why the surface of the contour filter is so much smoother that that of the iso volume filter? Can the same algorithm that is used to generate the surface area of the contour filter be used to generate the surface of the iso volume filter? This way the iso volume filter surface would look better and be more uniform. We could also match the contour and iso volume filter more constantly. I have attached an image that compares the iso volume filter with the contour filer for your reference. The contour filter is on the right and the Iso volume filter is being used on the left. This was constructed using disk\_out\_ref.ex2

 ![image](https://discourse.paraview.org/uploads/default/original/2X/3/3bfab47c433ba8dad2afab82a1b9c7973f71eaa1.jpeg)

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### Author: ![Kenneth\_Moreland](https://discourse.paraview.org/user_avatar/discourse.paraview.org/kenneth_moreland/32/15033_2.png) [@Kenneth\_Moreland](https://discourse.paraview.org/u/Kenneth_Moreland)
#### Post date: [June 21, 2023, 2:36pm UTC](https://discourse.paraview.org/t/contour-filter-vs-iso-volume-filter/12355/2 "2023-06-21T14:36:46Z")

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The output of the `Contour` filter is not any more smooth than `Iso Volume`. It just looks that way because the `Contour` filter is generating surface normals that provide smoother shading during rendering.

If you add the `Extract Surface` and then `Generate Surface Normals` filters to the output of `Iso Volume`, you will see that the added normals make the result look the same as `Contour`. Likewise, if you change the representation of both to `Surface With Edges`, you will notice that the two filters provide surfaces with the same facets (except that `Contour` triangulates its surface).

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### Author: ![wascott](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/w/8e8cbc/32.png) [@wascott](https://discourse.paraview.org/u/wascott)
#### Post date: [June 27, 2023, 2:17am UTC](https://discourse.paraview.org/t/contour-filter-vs-iso-volume-filter/12355/3 "2023-06-27T02:17:35Z")

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Thanks Ken. You nailed it, I wonder why I didn’t think of normals. The question actually came out of one of my classes, my trusty cohort Phil write it up.