Restart from VTK looses precision because data is written in single precision floating point format

The VTKWriter in Dune currently writes all data as "Float32", that's why when restarting from a vtk file we loose precision of our results.

I was thinking of proposing to optionally pass a data type to each VTKFunction (VTKFunction already stores other useful information about each field), extend the VTKFunction interface by a function that returns the data type (options would be Float32, Float64, Int32, Int64 at least, and probably an option/function that automatically converts a C++ type into a VTK data type), and use that in the VTKDataArrayWriter (defaulting to Float32 to retain current behaviour). Any other ideas? Otherwise I would draft something for Dune, but that can take some time...