It sounds like you need to convert your vectors of locations and velocities into gridded data, correct? One way to do this would be with the griddata command. For example, given some x and y locations ranging from 0 to 100 and the corresponding velocities u and v:
x = rand(100,1)*100;
y = rand(100,1)*100;
v = rand(100,1);
u = rand(100,1);
you can create a meshgrid of the x and y locations such that the meshgrid domain covers all possible x and y locations from your original data. Then use griddata to interpolate the scattered data onto the grid.
[xgrid,ygrid] = meshgrid(1:0.5:100,1:0.5:100);
vq = griddata(x,y,v,xgrid,ygrid);
uq = griddata(x,y,u,xgrid,ygrid);
