sampled extraction for cloud information

@Roger would like to extract cloud positions and some parcel characteristic (eg, diameter) into a simple list. If we have a sampledSet type that works directly/indirectly with cloud positions we could reuse the set writers for CSV output etc.

From Andy: tutorials/lagrangian/sprayFoam/aachenBomb/constant/sprayCloudProperties add

cloudFunctions
{
    bla
    {
        type            voidFraction;
    }
}

This will write a /sprayCloudTheta volScalarField with the void fraction.

Note: this only inserts into the cell holding the particle - there is no fancy intersection.

That has already been tested, and is not a solution when the particles are bigger than the target CFD mesh.

Currently being handled as an addOn solution

closed