Opening LIGGGTHS output VTK files in Python ↩

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created: 2022-07-08 16:01:55
modified: 2022-07-08 16:27:24

For this, we first need to install the vtk package using pip:

pip3 install vtk

Also numpy is needed, because we will load the files into numpy arrays:

pip3 install numpy

Then we can import them in the Python file along with the vtk_to_numpy function:

import numpy as np
import vtkmodules.all as vtk
from vtkmodules.util.numpy_support import vtk_to_numpy

Now we can create a reader and open the file. As an example:

reader = vtk.vtkPolyDataReader()
reader.SetFileName(f"../outfiles/{foldername}/{filename}")
reader.Update()
output = reader.GetOutput()

# Then retrieve the coordinate, velocity and orientation matrix of each particle
coords = vtk_to_numpy(output.GetPoints().GetData())
vs = vtk_to_numpy(output.GetPointData().GetArray(3))
orientations = vtk_to_numpy(output.GetPointData().GetArray(8))

Depending on the output file, we can also get other properties, like size, angular momentum, etc. If we want to figure out the index of a given property is, we need to print the properties of the reader. We can do it like this:

print(output.GetPointData())

And an example result of this, showing us the names and indices of properties:

...
  Array 0 name = id
  Array 1 name = type
  Array 2 name = mass
  Array 3 name = v
  Array 4 name = omega
  Array 5 name = shapex
  Array 6 name = shapey
  Array 7 name = shapez
  Array 8 name = TENSOR
  Array 9 name = blockiness1
  Array 10 name = blockiness2
...

The TENSOR member is the orthogonal matrix describing the orientation of the particle and the blockiness values are related to superquadrics.