  Performance of triple GEM prototypes in strong magnetic field has been
evaluated bymeans of a muon beam at the H4 line of the SPS test area at CERN.
Data have been reconstructedand analyzed offline with two reconstruction
methods: the charge centroid and the micro-Time-Projection-Chamber exploiting
the charge and the time measurement respectively. A combinationof the two
reconstruction methods is capable to guarantee a spatial resolution better than
150{\mu}min magnetic field up to a 1 T.
