A first model-independent measurement of the CKM angle \(\gamma \) has been performed with the \({{B} ^\pm } \rightarrow {D} h^\pm \) channels, with the subsequent four-body \({D} \rightarrow h^+h^-{{\pi } ^+} {{\pi } ^-} \) decays, where \(h = {K} \) or \({\pi } \) . To interpret the observed \(C\!P\) -violation effects in terms of \(\gamma \) , the complex resonance structure of these decays must be understood. Although amplitude models describe these decays well, reliable model uncertainties are difficult to evaluate. Specifically, the prediction of the \({{D} ^0} \) - \({{\overline{D}} ^0} \) strong-phase difference can potentially generate a systematic bias in the determination of \(\gamma \) .