  Experimental data for pion photoproduction including differential cross
sections and various polarization observables from four reaction channels,
$\gamma p \to \pi^0 p$, $\gamma p \to \pi^+n$, $\gamma n \to \pi^- p$ and
$\gamma n \to \pi^0 n$ from threshold up to $W=2.2$ GeV have been used in order
to perform a single-energy partial wave analysis with minimal model dependence
by imposing constraints from unitarity and fixed-$t$ analyticity in an
iterative procedure. Reaction models were only used as starting point in the
very first iteration. We demonstrate that with this procedure partial wave
amplitudes can be obtained which show only a minimal dependence on the initial
model assumptions.
  The analysis has been obtained in full isospin, and the Watson theorem is
enforced for energies below $W=1.3$ GeV but is even fulfilled up to $W\approx
1.6$ GeV in many partial waves. Electromagnetic multipoles $E_{\ell\pm}$ and
$M_{\ell\pm}$ are presented and discussed for $S,P,D$ and $F$-waves.
