  The INFN and INAF Italian research institutes developed a space-borne X-Ray
polarimetry experiment based on a X-Ray telescope, focussing the radiation on a
Gas Pixel Detector (GPD). The instrument obtains the polarization angle of the
absorbed photons from the direction of emission of the photoelectrons as
visualized in the GPD. Here we will show how we compute the angular resolution
of such an instrument.
