# Paraview Opacity problem
**URL:** https://discourse.paraview.org/t/paraview-opacity-problem/9329
**Category:** ParaView Support
**Tags:** vtk
**Created:** [April 2, 2022, 3:43am UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329 "2022-04-02T03:43:07Z")
**Posts on this page:** 12
**Page:** 1
### Author:  [@Yang](https://discourse.paraview.org/u/Yang)
#### Post date: [April 2, 2022, 3:43am UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329/1 "2022-04-02T03:43:07Z")
Hi, I am using ParaView to show a box. When I selected the opacity, it showed like below. How to get rid of the tetrahedron face?
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### Author:  [@Kenneth\_Moreland](https://discourse.paraview.org/u/Kenneth_Moreland)
#### Post date: [April 4, 2022, 1:12pm UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329/2 "2022-04-04T13:12:25Z")
It would help if you shared your data, but using the `Clean to Grid` filter might fix your problem.
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### Author:  [@Yang](https://discourse.paraview.org/u/Yang)
#### Post date: [May 14, 2022, 3:58am UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329/3 "2022-05-14T03:58:22Z")
Thanks for your suggestion. That works for me.
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### Author:  [@Yang](https://discourse.paraview.org/u/Yang)
#### Post date: [May 14, 2022, 5:27am UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329/4 "2022-05-14T05:27:33Z")
Hi Kenneth, that works well on a single server process, but when I start the server with mpi, e.g. `mpiexec -n 4`, the `clean to grid` won’t merge points on different processes. How to handle this case?
A data set is attached. Thanks!
[test.zip](https://discourse.paraview.org/uploads/short-url/sp6OAoekPGW6IYheF4cHxE51p5w.zip) (31.3 KB)
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### Author:  [@GregVernon](https://discourse.paraview.org/u/GregVernon)
#### Post date: [May 14, 2022, 6:16pm UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329/5 "2022-05-14T18:16:56Z")
> [@Yang](#):
>
> Hi Kenneth, that works well on a single server process, but when I start the server with mpi, e.g. `mpiexec -n 4`, the `clean to grid` won’t merge points on different processes. How to handle this case?
You might try the `D3` or `Redistribute DataSet` filters – I feel like one of those fixed this same issue I had several years ago.
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### Author:  [@Yang](https://discourse.paraview.org/u/Yang)
#### Post date: [May 15, 2022, 4:24am UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329/6 "2022-05-15T04:24:23Z")
@GregVernon The `D3` filter fixed this issue. Thank you very much!
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### Author:  [@GregVernon](https://discourse.paraview.org/u/GregVernon)
#### Post date: [May 18, 2022, 12:00am UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329/7 "2022-05-18T00:00:54Z")
@Kenneth_Moreland – while we’re on the topic… what is the reasoning behind the name of the `D3` filter? I’d argue that it’s impossible to know what it does from it’s name, it’s as useful as if it were named `H8`.
Is `D3` equivalent to the `Redistribute DataSet` filter? If so, should `D3` be removed / deprecated? At the very least, it seems like it should at least be renamed to `Repartition DataSet` [per its documentation](https://gitlab.kitware.com/paraview/paraview/-/blob/master/Remoting/Application/Resources/filters_filtersparallel.xml):
```xml
The D3 filter is
available when ParaView is run in parallel. It operates on
any type of data set to evenly divide it across the
processors into spatially contiguous regions. The output
of this filter is of type unstructured
grid.
```
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### Author:  [@wascott](https://discourse.paraview.org/u/wascott)
#### Post date: [May 18, 2022, 12:32am UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329/8 "2022-05-18T00:32:18Z")
Yang and Greg,
I believe there is a bit of confusion going on here.
The Redistribute Dataset filter does what it sounds like - it redistributes a dataset among multiple back end processors/cores/ranks, when using MPI. You really don’t want to use this to get rid of internal boundaries.
The Clean to Grid filter gets rid of redundant points within the files of one rank. When it is run on a butiltn server, it works on all of the dataset. This should get rid of internal boundaries between files. It will not get rid of boundaries between ranks.
The Ghost Cell Generator filter will effectively remove the boundaries between files on different ranks. Ken created a really good write-up on this in the Self Directed Tutorial (Help/ Self Directed Tutorial). Note that the Ghost Cell Generator filter has had some warts in the past, but is quite clean in master and the upcoming 5.11.0 release.
The D3 filter is older than dirt. It is basically a combination of the Redistribute Dataset filter and the Ghost Cell Generator (well, older versions of same). It is slow and takes lots of memory, but has been a very reliable tool for a lot of years. When the Ghost Cell Generator has had a year or so to prove it’s stability, D3 is slated to fade into the sunset.
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### Author:  [@Yang](https://discourse.paraview.org/u/Yang)
#### Post date: [May 21, 2022, 11:52am UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329/9 "2022-05-21T11:52:10Z")
@wascott Thank you so much for your detailed explanation!
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### Author:  [@Yang](https://discourse.paraview.org/u/Yang)
#### Post date: [May 22, 2022, 12:38pm UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329/10 "2022-05-22T12:38:56Z")
Hi @wascott, in my recent case, I need to use the filter `Ghost Cell Generator` twice to remove the boundaries between files on different ranks. Is there some reason behind the scenes?
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### Author:  [@wascott](https://discourse.paraview.org/u/wascott)
#### Post date: [May 23, 2022, 3:39pm UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329/11 "2022-05-23T15:39:47Z")
Hmmm… that is a surprise. You can adjust the number of ghost cell layers, I have never seen a need for this. Anyway, add 2 ghost cells? Alternatively, post an example dataset and include details how to replicate? If the dataset is too big, post screenshots before ghost cell generation, after the first ghost cell generation and again after the second ghost cell generation?
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### Author:  [@Yang](https://discourse.paraview.org/u/Yang)
#### Post date: [February 18, 2023, 2:27pm UTC](https://discourse.paraview.org/t/paraview-opacity-problem/9329/12 "2023-02-18T14:27:58Z")
Sorry for the late reply. 😅
In the new version Paraview 5.11, the problem is still there. I created 5 processes for the server. The screenshot is shown below as well as the data.
[test.tar.bz2](https://discourse.paraview.org/uploads/short-url/u61eKwiljKb9ElbleeuumR7JhuS.bz2) (3.6 MB)
Thank you for your time and attention to this matter.