Chessboard based on the geometry of the Boy surface [Echiquier basé sur la géométrie de la surface de Boy].
FX[x,y] = A11.PX[x,y] + A12.PY[x,y] + A13.PZ[x,y]
FY[x,y] = A21.PX[x,y] + A22.PY[x,y] + A23.PZ[x,y]