How to sort data cube in conversion of get_cell_cube?

[danlooo]

We need to convert a geographic data cube to a cell data cube.
We need to read chunks, that are sorted by lat/lon, because the cube might be bigger than memory.
However, we want to write the cell cube sorted by cell_id, or don't we?
Does cell id order matter, there just different files on the same hard drive...
However, if we load chunks of lat/lon tiles, we must load at least everything for one cell but mybe we load even more (rectangular convex hull).
Maybe it is better to do this:

for cell_id in 1::num_cells:
    boundariy = get_boundary(grid, cell_id)
    chunck = get_chunk(boundary, geo_cube)
    cell_cube[cell_id] = mean(chunck)

Currently, we load rectangular lon/lat tile chunks and use matrix vector multiplication.