I am trying to make a PIC (particle in cell) fluid simulation, but I cannot figure out how the transfer of data (velocity, density…) from particles to the cells is supposed to work.

Looking at this youtube video on the basic ideas of PIC/FLIP, they mention bilinear interpolation from the particle to the corners of a cell, but later when talking about solving the cells (for incompressibility) the velocity is on the edges of the cells.

Also, in this paper on page 22, there is a drawing of the grid layout with the data being stored on the edges instead of the corners. From the end of page 26 to mid-page 28 they talk about the transfer methods, but I don’t fully understand how to use the info they give.

If someone could clarify how the particle to cell transfer is supposed to be done, it would help a ton!