[Paraview] snappy display of inner points of large grid

[Donjan Rodic]

I'm visualising a large grid dataset with different regions == scalar 
colors with ParaView 5.1.2 on Ubuntu 16.10.

The computation prints the colors (floats in [0,1]) of a 250^3 (usually 
larger) grid into a CSV file:
x,y,z,color
0,0,0,0.5
0,0,1,0.5
0,0,2,0.3
...

I load it with ParaView (Python script), apply TableToPoints, set 
points.XColumn = 'x', etc. and the Points representation.
This works really well with opacity mapping and sliding the Mapping Data 
curve to highlight the different regions inside the grid.
The main problem is the large size (hundreds of MB) of the CSV files. 
Since the grid is rectilinear and equidistant, verbose x,y,z columns are 
wasteful.

Writing into a legacy VTK file with STRUCTURED_POINTS yields a nice 7x 
size reduction, but then in ParaView the inner points are not displayed.
I've tried using the Glyph representation, which makes the rendering 
unusably slow (10+ seconds for a small rotation).
2D Glyphs with Glyph Type Vertex are not noticeably faster and lose 
coloring.
Applying the Shrink filter (random googled hint) freezes the GUI for 
more than 5 minutes before I kill it. At smaller system sizes the 
performance is bad.

For the CSV->TableToPoints described initially, the resulting data 
structure is shown in the Information tab as a Polygonal Mesh with 1 
single cell and 15 million points, Memory: 600 MB. After loading it 
responds and rotates snappily on a recent Core i7 & NVidia GPU.
The VTK file loads with several million cells as well as 15 million 
points, and a Image (Uniform Rectilinear Grid) type. Memory: 15 MB ... 
much lower but irrelevant with 16 GB RAM.

It appears what I want is to have all points in one single cell, and the 
CSV reader is the only one I've found doing the right thing.

Using RECTILINEAR_GRID and custom CELL_DATA in the VTK file doesn't 
help: the format apparently doesn't allow to specify less than 1 cell 
per 8 vertices (or 4 in 2D).
Next I've tried to use a raw format, but after setting it up, ParaView 
insists on creating millions of cells. Same experience as with VTK.
I've also tried ExtractSurface to at least get a Polygonal Mesh from the 
Rectilinear Grid: still too slow and too many cells.

Something like a "GridToTable" filter with a subsequent TableToPoints 
would do the job, but I can't find such a function. Or a routine to 
merge all cells into one.

Creating a custom filter via GUI doesn't work because the loaded 
data.vtk "does not have any inputs".

How do I achieve the same performance and display of inner points as 
CSV->TableToPoints with either another file format or from the Grid data 
structure offered by the VTK file reader?

cheers
Donjan

PS: googling for
   paraview grid "to table"
mainly yields results for a typo in the documentation of 
TableToStructuredGrid, saying "Converts to table to structured....".