What is the approach to transfer the activity packets in posecells?

[SeaEastXu]

    %extend the Posecells one unit in each direction (max supported at the moment)
    % work out the weight contribution to the NE cell from the SW, NW, SE cells 
    % given vtrans and the direction
    % weight_sw = v * cos(th) * v * sin(th)
    % weight_se = (1 - v * cos(th)) * v * sin(th)
    % weight_nw = (1 - v * sin(th)) * v * sin(th)
    % weight_ne = 1 - weight_sw - weight_se - weight_nw
    % think in terms of NE divided into 4 rectangles with the sides
    % given by vtrans and the angle
    pca_new=zeros(PC_DIM_XY+2);            
    pca_new(2:end-1,2:end-1) = pca90;
    weight_sw = vtrans^2 *cos(dir90) * sin(dir90);
    weight_se = vtrans*sin(dir90) - vtrans^2 *cos(dir90) * sin(dir90);
    weight_nw = vtrans*cos(dir90) - vtrans^2 *cos(dir90) * sin(dir90);
    weight_ne = 1.0 - weight_sw - weight_se - weight_nw;

    % circular shift and multiple by the contributing weight
    % copy those shifted elements for the wrap around       
    pca_new = pca_new.*weight_ne + circshift(pca_new, [0 1]).*weight_nw + circshift(pca_new, [1 0]).*weight_se + circshift(pca_new, [1 1]).*weight_sw;
    pca90 = pca_new(2:end-1,2:end-1);
    pca90(2:end,1) = pca90(2:end,1) + pca_new(3:end-1,end);
    pca90(1,2:end) = pca90(1,2:end) + pca_new(end,3:end-1);
    pca90(1,1) = pca90(1,1) + pca_new(end:end);

    % unrotate the pose cell xy layer
    Posecells(:,:,dir_pc) = rot90(pca90, 4 - floor(dir * 2/pi));

I don't konw the funciton of these codes.