# VTKHDF format

**URL:** https://discourse.paraview.org/t/vtkhdf-format/13203
**Category:** ParaView Support
**Created:** [November 8, 2023, 7:13am UTC](https://discourse.paraview.org/t/vtkhdf-format/13203 "2023-11-08T07:13:17Z")
**Posts on this page:** 5
**Page:** 1

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### Author: ![Frankx9](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/f/3e96dc/32.png) [@Frankx9](https://discourse.paraview.org/u/Frankx9)
#### Post date: [November 8, 2023, 7:13am UTC](https://discourse.paraview.org/t/vtkhdf-format/13203/1 "2023-11-08T07:13:17Z")

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Hello,

I have two VTKHDF dataset, one with the full flowfield and one with only surface data, is there a way to combine those dataset into one VTKHDF? If so, can this be done also at writing time? What should be the VTKHDF file structure to achieve that?

Best regards

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### Author: ![mwestphal](https://discourse.paraview.org/user_avatar/discourse.paraview.org/mwestphal/32/17_2.png) [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [November 8, 2023, 8:32am UTC](https://discourse.paraview.org/t/vtkhdf-format/13203/2 "2023-11-08T08:32:35Z")

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@Lucas_Givord

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### Author: ![Lucas\_Givord](https://discourse.paraview.org/user_avatar/discourse.paraview.org/lucas_givord/32/6851_2.png) [@Lucas\_Givord](https://discourse.paraview.org/u/Lucas_Givord)
#### Post date: [November 8, 2023, 8:45am UTC](https://discourse.paraview.org/t/vtkhdf-format/13203/3 "2023-11-08T08:45:51Z")

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Hello @Frankx9,

What datatype are you using for these 2 vtkhdf file? PolyData? UnstructuredGrid?

We actively work on extending the VTKHDF file format to have composite data set, the design proposal is here:

> **[Composite Data Sets for the VTKHDF format](https://discourse.vtk.org/t/composite-data-sets-for-the-vtkhdf-format/12190)**
>
> This thread is dedicated to proposing a new design for the VTKHDF format that would describe vtkPartitionedDataSetCollections and vtkMultiBlockDataSets. The general idea is to have an Assembly group in the file that describes the composite data...

So when it will be done, the best way to handle your use case will be to use it.

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### Author: ![Frankx9](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/f/3e96dc/32.png) [@Frankx9](https://discourse.paraview.org/u/Frankx9)
#### Post date: [November 8, 2023, 8:47am UTC](https://discourse.paraview.org/t/vtkhdf-format/13203/4 "2023-11-08T08:47:40Z")

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Hello,

I’m using unstructured grids at the moment

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### Author: ![Lucas\_Givord](https://discourse.paraview.org/user_avatar/discourse.paraview.org/lucas_givord/32/6851_2.png) [@Lucas\_Givord](https://discourse.paraview.org/u/Lucas_Givord)
#### Post date: [November 8, 2023, 8:53am UTC](https://discourse.paraview.org/t/vtkhdf-format/13203/5 "2023-11-08T08:53:09Z")

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ok, so the best way still be to use the future composite support in vtkhdf file format which will contained your 2 UnstruturedGrid.

I will keep you up to date about any improvement in vtkhdf file format regarding your use case