  A rigorous multipole analysis of the recent {\gamma}p -> \pi^{0}p cross
section measurement is presented. The data were taken using the photon
spectrometer TAPS at the tagged photon beam of the Mainz microtron. The s and p
wave multipoles were extracted using minimal model assumptions. The predicted
unitary cusp for the s wave multipole E_{0+} due to the two step {\gamma}p ->
\pi^{+}n -> \pi^{0}p reaction was observed. The results are consistent with one
loop chiral perturbation theory calculations for which three low energy
constants have been determined by a fit to the data. The uncertainties in the
analysis and the need for polarization observables are discussed.
