  Azimuthally differential femtoscopic measurements, being sensitive to
spatio-temporal characteristics of the source as well as to the collective
velocity fields at freeze-out, provide very important information on the nature
and dynamics of the system evolution. While the HBT radii modulations relative
to the second harmonic event plane reflect mostly the spatial geometry of the
source, the third harmonic results are mostly defined by the velocity fields.
Radii variations with respect to the third harmonic event plane unambiguously
signal a collective expansion and anisotropy in the flow fields. Event shape
engineering (ESE) is a technique proposed to select events corresponding to a
particular shape. Azimuthally differential HBT combined with ESE allows for a
detailed analysis of the relation between initial geometry, anisotropic flow
and the deformation of source shape. We present azimuthally differential pion
femtoscopy with respect to second and third harmonic event planes as a function
of the pion transverse momentum for different collision centralities in Pb-Pb
collisions at sqrt(s_NN) = 2.76 TeV. All these results are compared to existing
models. The effects of the selection of the events with high elliptic or
triangular flow are also presented.
