  The nature of coronal wave fronts is deeply debated. They are observed in
several wavelength bandpasses in spectra, and are frequently interpreted as
magnetosonic waves propagating in the lower solar atmosphere. However, they can
be attributed to the line of sight projection of the edges of coronal mass
ejections. Therefore, the altitude estimation of these features is crucial to
discriminate in favor of one of these two interpretations. We take advantage of
a set of observations obtained from two different points of view by
EUVI/SECCHI/STEREO on December, 7th 2007 to derive the time evolution of the
altitude of a coronal wave front. We develop a new technique to compute the
altitude.
  We find that the observed brightness has an increasing altitude during 5
minutes, then the altitude decreases slightly back to the low corona. We
interpret the evolution of the altitude as following: the increase of altitude
of the wave front is linked to the rise of a bubble like structure whether it
is a magnetosonic wave front or a CME in the first phase. During the second
phase, the observed brightness is mixed with the brightening of the underlying
magnetic structures as the emission of the plasma of the wave front fades due
to the plasma dilution with the altitude.
