  Recent observations of radio relics - diffuse radio emission in galaxy
clusters - have revealed that these sources are not smooth but consist of
structures in the form of threads and filaments. We investigate the origin of
these filamentary structures and the role of projection effects. To this end,
we have developed a tool that extracts the filamentary structures from
background emission. Moreover, it is capable of studying both two-dimensional
and three-dimensional objects. We apply our structure extractor to, both,
observations and cosmological simulations of radio relics. Using Minkowski
functionals, we determine the shape of the identified structures. In our 2D
analysis, we find that the brightest structures in the observed and simulated
maps are filaments. Our analysis of the 3D simulation data shows that radio
relics do not consist of sheets but only of filaments and ribbons. Furthermore,
we did not find any measurable projection effects that could hide any
sheet-like structures in projection. We find that, both, the magnetic field and
the shock front consist of filaments and ribbons that cause filamentary radio
emission.
