# Stepping through Group Import in Volume Representation

**URL:** https://discourse.paraview.org/t/stepping-through-group-import-in-volume-representation/8692
**Category:** ParaView Support
**Tags:** python
**Created:** [December 24, 2021, 8:58am UTC](https://discourse.paraview.org/t/stepping-through-group-import-in-volume-representation/8692 "2021-12-24T08:58:33Z")
**Posts on this page:** 1
**Page:** 1

<div class="post-metadata">

### Author: ![waveman](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/w/e95f7d/32.png) [@waveman](https://discourse.paraview.org/u/waveman)
#### Post date: [December 24, 2021, 8:58am UTC](https://discourse.paraview.org/t/stepping-through-group-import-in-volume-representation/8692/1 "2021-12-24T08:58:33Z")

</div>

My process is as follows:

1. Import a group of .vtk data
2. Change the Represtation to Volume
3. The coloring automatically changes to the data array name (there is only one per file).
4. Go to the next time (data) step.

Coloring immediately has a problem:

```auto
ERROR: In /builds/gitlab-kitware-sciviz-ci/build/superbuild/paraview/src/VTK/Common/ExecutionModel/vtkCompositeDataPipeline.cxx, line 154
vtkPVDataRepresentationPipeline (0x1a3f7960): Can not execute simple algorithm without output ports

ERROR: In /builds/gitlab-kitware-sciviz-ci/build/superbuild/paraview/src/VTK/Rendering/VolumeOpenGL2/vtkSmartVolumeMapper.cxx, line 279
vtkSmartVolumeMapper (0x18a39a90): Could not find the requested vtkDataArray! 3, 1, -1, data0001

```

I have used multiple different strategies to avoid this, but can’t seem to get it right. I know the extent of the data but have not found a way to properly create a LUT for this.

```auto
my_lut = pv.MakeBlueToRedLT(0, 1)

array_info = reader.PointData[data_array_name]
display1.RescaleTransferFunctionToDataRange(True, False)
AssignLookupTable(array_info, my_lut)

```

This results in a new error:

```auto
Traceback (most recent call last):
  File "<string>", line 37, in <module>
  File "/home/.../src/animate_data.py", line 73, in prepare_animation
    pv.AssignLookupTable(array_info, self.wf_lut)
  File ".../ParaView-5.9.1-MPI-Linux-Python3.8-64bit/lib/python3.8/site-packages/paraview/simple.py", line 1761, in AssignLookupTable
    if not presets.HasPreset(lutName):
TypeError: HasPreset argument 1: string or None required

```

Does anyone have an idea to get around the coloring TransferFunction catch22?