Dalitz plot analysis of three-body Charmonium Decays at BaBar

We present preliminary results on the measurement of the I=1/2 $K\pi$ $\mathcal{S}$-wave through a model independent partial wave analysis of ${\eta }_c$ decays to $K_S^0{K}^{+}{\pi }^{-}$ and $K^{+}{K}^{-}{\pi }^0$ produced in two-photon interactions. We also perform a Dalitz plot analysis of the $J\mathrm{/}\psi$ decays to ${\pi }^{+}{\pi }^{-}{\pi }^0$ and $K^{+}{K}^{-}{\pi }^0$ produced by the initial state radiation process.