# SPHVolumeInterpolator with cutoff array

**URL:** https://discourse.paraview.org/t/sphvolumeinterpolator-with-cutoff-array/3119
**Category:** ParaView Support
**Created:** [December 4, 2019, 4:24pm UTC](https://discourse.paraview.org/t/sphvolumeinterpolator-with-cutoff-array/3119 "2019-12-04T16:24:11Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![cms](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/c/76d3ee/32.png) [@cms](https://discourse.paraview.org/u/cms)
#### Post date: [December 4, 2019, 4:24pm UTC](https://discourse.paraview.org/t/sphvolumeinterpolator-with-cutoff-array/3119/1 "2019-12-04T16:24:11Z")

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Hi,

I’m trying to use the SPHVolumeInterpolator to create a volume rendering image from a SPH particle  
distribution. I get nice results with a fixed smoothing length (= fixed spatial step).  
However, my simulation uses variable smoothing lengths and I tried to use the smoothing lengths from the simulation as the cutoff array, but all nodes/interpolated values are zero then.  
I’ve found the following information from two years ago and was wondering, if the cutoff array now works:  
[https://public.kitware.com/pipermail/paraview/2017-March/039713.html](https://public.kitware.com/pipermail/paraview/2017-March/039713.html)

So, just to get it right: for a standard SPH kernel sum: rho\_i = \sum\_j m\_j W\_ij(h\_i,h\_j) how do I specify the smoothing lengths in the array selection for density, mass and cutoff array and which spatial step do I have to insert then?

Thanks

Christoph

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### Author: ![jfavre](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/j/b5ac83/32.png) [@jfavre](https://discourse.paraview.org/u/jfavre)
#### Post date: [October 20, 2021, 9:35am UTC](https://discourse.paraview.org/t/sphvolumeinterpolator-with-cutoff-array/3119/2 "2021-10-20T09:35:41Z")

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The following commit [https://gitlab.kitware.com/vtk/vtk/-/commit/cabbdb3ab1f816bd1b2595c21d88de80b26b5895](https://gitlab.kitware.com/vtk/vtk/-/commit/cabbdb3ab1f816bd1b2595c21d88de80b26b5895) corrected previous mis-understandings about the cutoff distance. It supports the fact that the cutoff array should be defined in the input point data, not in the source point data.  
The problem remains with the ParaView GUI (v5.10-RC1 tested). The Array Selections lets you choose _all_ arrays (Density, Mass and Cutoff) from the source point data, and it fails silently if you provide your own smoothing length array’s name, since that array is not attached to the probing object (Line, Plane or Volume).