Extract velocity, pressure, and density data on lattices without interpolation

[jjessberger]

Writing point data for each point with CSVwriter, then you have to perform the iteration over the points yourself. It will be slow because of a lack of parallelization. Cf. e.g. examples laminar/poiseuille2d where this is done for a plot-over-line with GnuplotWriter (it works similar + creates a Gnuplot plot).

Vtm files that contain point coordinates + functor data are written by the SuperVtmWriter – this is originally intended for Paraview visualization but you can as well use the datafiles for your own purpose. It includes a parallelized iteration over the lattice points. This is what I’d recommend to use. It’s simpler to run a postprocessing script over the vtm files than to create the output completely on your own.

Since it is made for HPC application, the design for storing the data is rather complex. Well, in the end it all breaks down to arrays. Each BlockLattice holds data (at least provides an interface) to the nodes in that cuboid. If you’re eager, you can have a deep look into what this class does…

[danial]

This might be a bit late to answer but what I found useful when trying to get the data in CSV format in the lattice points and not interpolated points, is to just let OpenLB dump the data into pvd/vtm/vti regularly, then use VTK library in python to read the vti data into numpy arrays. There will be some overlapping points from the MPI tiles and if you need to remove those overlapping points and just end up with unique lattice points that needs another step of processing. The method mentioned in this thread looks interesting though because it doesn’t need python & VTK and can be done within OpenLB c++ codes itself, I should give it a try.

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