  We present a combined analysis of elliptic and triangular flow data from LHC
and RHIC using viscous relativistic hydrodynamics. Elliptic flow $v_2$ in
hydrodynamics is proportional to the participant eccentricity $\varepsilon_2$
and triangular flow is proportional to the participant triangularity
$\varepsilon_3$, which means $v_n=C_n\varepsilon_n$, where $C_n$ is the linear
response coefficient in harmonic n. Experimental data for $v_2$ and $v_3$
combined with hydrodynamic calculations of $C_n$ thus provide us with the rms
values of initial anisotropies $\varepsilon_2$ and $\varepsilon_3$. By varying
free parameters in the hydro calculation (in particular the shear viscosity),
we obtain an allowed band in the (rms $\varepsilon_2$, rms $\varepsilon_3$)
plane. Comparison with Monte-Carlo models of the initial state allows us to
exclude several of these models. We illustrate that the effect of changing the
granularity of the initial state is similar to changing the medium properties,
making these effects difficult to disentangle.
