Reply To: How to understand vti files
The SuperGeometry(2,3)D stores a vector of BlockGeometry(2,3)D instances (this pattern is present all throughout OpenLB), one for each cuboid assigned to the process. At the lowest level, all material numbers of a block are stored in a plain array.
It should be possible to write raw XML VTK files by setting compress=false in the SuperVTMwriter3D constructor.