  There has been a puzzle between experiments and theoretical predictions on
the charge ordering of layered titanium-oxypnictides superconductors.
Unconventional mechanisms to explain this discrepancy have been argued so far,
even affecting the understanding of superconductivity on the compound. We
provide a new theoretical prediction, by which the discrepancy itself is
resolved without any complicated unconventional explanation. Phonon dispersions
and changes of nesting vectors in Fermi surfaces are clarified to lead to the
variety of superlattice structures even for the common crystal structures when
without CDW, including orthorhombic $2 \times 2 \times 1$ one for
BaTi$_2$As$_2$O, which has not yet been explained successfully so far, being
different from tetragonal $\sqrt{2} \times \sqrt{2} \times 1$ for
BaTi$_2$Sb$_2$O and BaTi$_2$Bi$_2$O. The electronic structure analysis can
naturally explain experimental observations about CDW including most latest
ones without any cramped unconventional mechanisms.
