  Evolved stars are among the largest and brightest stars and they are ideal
targets for the new generation of sensitive, high resolution instrumentation
that pro- vides spectrophotometric, interferometric, astrometric, and imaging
observables. The interpretation of the complex stellar surface images requires
numerical simulations of stellar convection that take into account
multi-dimensional time-dependent radiation hydrodynamics with realistic input
physics. We show how the evolved star simulations are obtained using the
radiative hydrodynamics code CO5BOLD and how the accurate observables are
computed with the post-processing radiative transfer code Optim3D. The synergy
between observations and theoretical work is supported by a proper and
quantitative analysis using these simulations, and by strong constraints from
the obser- vational side.
