Add possiblity to create ".pvd"-files in vtk-writer

Currently, the files that are written in pystencil's vtk-writer are stored as vtkImageData (.vti) only. It would be great if the vtk-writer was able to create a file in ParaView Data format (.pvd) which contains the path to each .vti-file and the (LBM) time step at which the file was written.

In ParaView, "time" would then actually represent the (LBM) time step instead of being equal to the index, i.e., number of the loaded ".vti"-file.

added feature label

Do you have a simple jupyter notebook or python script as a test case?

assigned to @holzer

changed milestone to %Release 1.1

I had totally forgotten about this issue - sorry for not-answering earlier.

Consider the following example:

import numpy as np
import pystencils as ps

dh = ps.create_data_handling(domain_size=(1, 1))
src_field = dh.add_array("array", values_per_cell=1, ghost_layers=0)
src = dh.fill("array", 0.0)

vtk_writer = dh.create_vtk_writer("vtk-out/", ["array"])
vtk_output_frequency  = 10

timesteps = 50

for t in range(timesteps):
    if(t % vtk_output_frequency == 0):
        vtk_writer(t)

Assume that the value of t has a physical or numerical meaning. In the code snippet above, 6 .vti files with filename corresponding to the variable t are created. However, when loading this file-series in ParaView, the Time ranges from 0 to 5 and the filename, i.e., t is ignored.

For this purpose, there exists the ParaView Data format (.pvd). There, a variable named timestep specifies which Time is displayed when opening this file. For the example above, the .pvd file could look like:

<?xml version="1.0"?>
<VTKFile type="Collection">
	<Collection>
		<DataSet timestep="0" group="" part="0" file="_00000000.vti" />
		<DataSet timestep="10" group="" part="0" file="_00000010.vti" />
		<DataSet timestep="20" group="" part="0" file="_00000020.vti" />
                <DataSet timestep="30" group="" part="0" file="_00000030.vti" />
		<DataSet timestep="40" group="" part="0" file="_00000040.vti" />
		<DataSet timestep="50" group="" part="0" file="_00000050.vti" />
	</Collection>
</VTKFile>

Note, that the actual filename can be arbitrary and must not be identical to timestep.

In summary, it would be great if pystencils offered functionality to automatically create such .pvd-files. Especially for LBM simulations with lbmpy, a correctly displayed Time in ParaView simplifies the user-experience quite significantly.

assigned to @hoenig and unassigned @holzer

assigned to @holzer and unassigned @hoenig