# Normals of slices not appearing in the calculator filter
**URL:** https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104
**Category:** ParaView Support
**Created:** [September 30, 2021, 3:31pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104 "2021-09-30T15:31:47Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@TimJim](https://discourse.paraview.org/u/TimJim)
#### Post date: [September 30, 2021, 3:31pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/1 "2021-09-30T15:31:47Z")
Hi - this might be a simple question but is it possible to get surface normals that are usable in calculator filters from slices?
Normally, for a 3D surface, I can do Extract Surface → Generate Surface Normal → Calculator and Normals\_X, Normals\_Y, and Normals\_Z are available, but when I tried to first take a slice first, and then do the pipeline on the slice, I can’t seem to access normals any more.
Is this the expected behaviour? If so, what would the correct way to extract normals from a closed 2D slice? In my case, I have sliced a wing, so I have a aerofoil section.
Thanks!
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### Author:  [@wascott](https://discourse.paraview.org/u/wascott)
#### Post date: [September 30, 2021, 4:19pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/2 "2021-09-30T16:19:52Z")
Generate surface normals? The following works for me. Please give us the exact steps and a small dataset to try if this doesn’t work.
- 5.10.0-RC1
- Load disk\_out\_ref.exo from the Examples directory. Apply.
- Slice. Apply. Turn off the plane tool visibility.
- Generate Surface Normals.
The reason we probably need a dataset is there may be an incompatibility between your data type and generate surface normals?
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### Author:  [@TimJim](https://discourse.paraview.org/u/TimJim)
#### Post date: [September 30, 2021, 4:43pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/3 "2021-09-30T16:43:28Z")
Hi Walter. Where are the examples located? I searched for them in my Paraview directory paths but was able to find any .exo files.
In the meantime, please see attached for a PVSM state file [slice\_wing\_no\_normal.pvsm](https://discourse.paraview.org/uploads/short-url/lRHRtJU1oAu7CqDdPynjwVeaQQR.pvsm) (360.2 KB)
and here for the flow surface: [surface\_flow\_0.vtu](https://drive.google.com/file/d/15OftxGAl2hwp84CjgYlvvVBNw23ZNHX_/view?usp=sharing)
I’m running Paraview 5.8.1 and in the state file, I have done slice, generate surface normals, and opened a calculator to check if there are any normals. In my case, they are not present under the Vectors dropdown.
(The surface flow file was output from SU2.)
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### Author:  [@wascott](https://discourse.paraview.org/u/wascott)
#### Post date: [September 30, 2021, 4:57pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/4 "2021-09-30T16:57:45Z")
File/ Open / Upper left corner.
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### Author:  [@TimJim](https://discourse.paraview.org/u/TimJim)
#### Post date: [September 30, 2021, 5:05pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/5 "2021-09-30T17:05:48Z")
I did see you post that before but unfortunately, I don’t have it.
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### Author:  [@wascott](https://discourse.paraview.org/u/wascott)
#### Post date: [September 30, 2021, 5:16pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/6 "2021-09-30T17:16:21Z")
It’s because you have built your own ParaView., or are connected to a cluster.
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### Author:  [@TimJim](https://discourse.paraview.org/u/TimJim)
#### Post date: [September 30, 2021, 6:48pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/7 "2021-09-30T18:48:29Z")
Thanks for the hint - I downloaded the 5.9.1 binary for testing and I can confirm that using the .exo, the normals are present in the Calculator filter after calling Generate Surface Normals on a Slice, but not the .vtu geometry I had attached in the above post.
Would you be able to confirm if you are also unable to extract the normals on the .vtu geometry?
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### Author:  [@wascott](https://discourse.paraview.org/u/wascott)
#### Post date: [September 30, 2021, 6:59pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/8 "2021-09-30T18:59:14Z")
@mwestphal @cory.quammen Hi guys. This dataset, a vtu file (Unstructured Grid) doesn’t let us run the Generate Surface Normals filter. Any idea why? Shouldn’t it just natively run? The dataset is a 3d surface unstructured grid.
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### Author:  [@wascott](https://discourse.paraview.org/u/wascott)
#### Post date: [September 30, 2021, 7:01pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/9 "2021-09-30T19:01:06Z")
Hey Tim. The issue is that the dataset isn’t compatible with the input needs of the Generate Surface Normals filter. Run the Extract Surface filter on it (converting from Unstructured to Polygonal mesh), THEN the Generate Surface Normals filter.
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### Author:  [@TimJim](https://discourse.paraview.org/u/TimJim)
#### Post date: [September 30, 2021, 7:04pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/10 "2021-09-30T19:04:04Z")
Hi Walter - I did try that on the previous version. I just double checked on 5.9.1 and it still doesn’t work for me:
Did you see the normals on your installation?
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### Author:  [@TimJim](https://discourse.paraview.org/u/TimJim)
#### Post date: [September 30, 2021, 7:15pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/11 "2021-09-30T19:15:32Z")
I just experimented with clip instead of slice. If I set a very thin box clip, then I can extract surface normals but would this be a bad approach in terms of memory?
For example if I create several hundred cuts along the wing to integrate the pressures on each sectional cut, (since my end goal is to integrate each section), would this be better done with many slices or many very slim box clips?
To stay on thread - what makes slice behave differently from clip? Thanks.
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### Author:  [@wascott](https://discourse.paraview.org/u/wascott)
#### Post date: [September 30, 2021, 7:26pm UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/12 "2021-09-30T19:26:08Z")
Don’t do the slice. You already have your surface. Here is what I did.
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### Author:  [@TimJim](https://discourse.paraview.org/u/TimJim)
#### Post date: [October 1, 2021, 5:54am UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/13 "2021-10-01T05:54:49Z")
Hi Walter - sorry, I don’t think I understood you (or I explained the target poorly). My goal is to get slices so that I can see the local cross-sectional pressures. Then would like to integrate each 2D slice for a local lift coefficient, so that I can produce a plot like this:
Did you mean that I could achieve the same thing without taking slices? Thanks.
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 1, 2021, 8:08am UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/14 "2021-10-01T08:08:21Z")
so you want to produce slices like this one ? :
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### Author:  [@TimJim](https://discourse.paraview.org/u/TimJim)
#### Post date: [October 1, 2021, 8:32am UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/15 "2021-10-01T08:32:16Z")
Hi Mathieu, thanks - yes, just in the the Y-normal axis! So Like this:
So that I can get something like this for each section:
Then I can integrate each section for the desired local lift.
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 1, 2021, 8:42am UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/16 "2021-10-01T08:42:23Z")
So what is missing for you here ?
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### Author:  [@TimJim](https://discourse.paraview.org/u/TimJim)
#### Post date: [October 1, 2021, 8:43am UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/17 "2021-10-01T08:43:27Z")
I can’t get the normals from a slice in the calculator filter!
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 1, 2021, 8:49am UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/18 "2021-10-01T08:49:20Z")
Ok, got it, do as follows:
- Open surface\_flow.vtu, Apply
- ExtractSurface, Apply
- GenerateSurfaceNormals, Apply
- Slice, Y axis, Apply
- (Optinal, Glyph with normals, Apply)
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### Author:  [@TimJim](https://discourse.paraview.org/u/TimJim)
#### Post date: [October 1, 2021, 9:02am UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/19 "2021-10-01T09:02:34Z")
Fantastic, that solved the issue. Thanks for your help Walter & Mathieu! So the solutions is to extract the surface and get the normals before slicing.
How come for a clip, we can still get the normals after clipping? Is this because slices loose surface information as they are ‘infinitely thin’? Thanks for your help.
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 1, 2021, 9:07am UTC](https://discourse.paraview.org/t/normals-of-slices-not-appearing-in-the-calculator-filter/8104/20 "2021-10-01T09:07:23Z")
> [@TimJim](#):
>
> How come for a clip, we can still get the normals after clipping? Is this because slices loose surface information as they are ‘infinitely thin’? Thanks for your help.
Yes.