Visualizing rho and u in Paraview about fluidx3d

[ProjectPhysX]

Hi @aiotko,

ParaView offers 2 Representation options for visualizing volumetric data:

• Slice: for velocity you can also select between Magnitude or X/Y/Z components
  
• Volume: for density you can also use Shade+Show Isosurfaces
  

Unfortunately, ParaView can't do Q-criterion isosurface like my built-in rendering engine.

Kind regards,
Moritz

[aiotko]

Thank you for your explanation, @ProjectPhysX,

I'm just looking for a way to visualize Q-criterion isosurface from VTK output by pyvista or vtk in Python or C++ to have a view like in your engine since it's pretty useful.

Maybe you have an example of how to do it?

[ProjectPhysX]

ParaView can't do Q-criterion isosurfaces out-of-the-box unfortunately from 3-component vector data. This is how it's implemented in FluidX3D:

• for each of 8 cells in a cube, calculate the Q-value from a 6-point stencil
• calculate vertex positions of up to 5 triangles with marching-cubes
• color triangles based on interpolated velocity/color/temperature
• rasterize triangles

You'd have to copy the part to calculate the Q-value for each cell to your C++ setup and run it on the entire grid on CPU; you can temporarily store Q-values in the lbm.rho data field. Then export it to .vtk and let paraview draw the isosurfaces - without coloring though.