  Knowledge of the intrinsic shape of galaxy clusters is very important in
investigating cosmic structure formation and astrophysical processes. The
reconstruction of the 3-dimensional structure usually relies on deprojecting
2-dimensional X-ray, Sunyaev-Zeldovich (SZ) and/or gravitational lensing
observations. As known, a joint analysis of these data sets can provide the
elongation of the cluster along the line of sight together with its length and
width in the plane of the sky. An unbiased measurement of the Hubble constant
can be also inferred. Due to some intrinsic degeneracies, the observational
constraints obtained from such projected data-sets are not enough to allow an
unique inversion. In general, the projected maps can be at the same time
compatible with prolate, oblate and with many triaxial configurations. Even a
prolate cluster might be interpreted as an oblate system and vice versa.
Assuming that the cluster is axially symmetric is likely to overestimate the
intrinsic ellipticity, whereas the system always looks rounder performing the
inversion under the hypothesis of a triaxial cluster aligned with the line of
sight. In general, analysing triaxial clusters under the prolate or oblate
assumption may introduce strong biases even when the clusters are actually near
to axial symmetry whereas the systematics introduced assuming the cluster to be
aligned with the line of sight are more under control.
