This is has code ripped out of ROMS for computing the i,j positions of floats initialized with lat,lon positions. This code has things hard-coded for NEP6, I'm afraid, including reading the floats_NEP.in file. This hard-coding happens in get_grid.f95 for the grid filename and in main3d.f95 for the grid dimensions and vertical stretching parameters, plus of course the name of the floats.in file. Then there's hindices, currently hard-coded for the Arctic, where going "north" of the North Pole is problematic.