hipjointcentrePiG_data

 data = HIPJOINTCENTREPIG_DATA(data,test) computes left and right hip joint centers for
 plug-in gait (PiG) marker data

 ARGUMENTS
  data      ... Zoo data containing PiG markers. Required markers are 'RASI','LASI','SACR'
                or 'RASI','LASI','RPSI','LPSI'
  test      ... Tests against PiG values, if available (boolean). Default: false

 RETURNS
  data      ... Zoo data with appended hip joint center virtual marker as RHipJC and LHipJC.
  localjc   ... Coordinates of the hip joint centre (struct) in local coordinates

 NOTES
 - computation method based on Davis et al. "A gait analysis data collection and reduction
   technique". Hum Mov Sci. 1991. (see also PiG manual)
 - If zoo files don't contain anthro data (e.g. contain only PiG markers), user must add
   these fields to zoo files in a previous step, or enter antrho values as arguments
 - root mean squared error between the Vicon and custom calculation of the magitude of the
   hip joint centre position stored in the hip joint centre channel event branch

 See also bmech_jointcentrePiG, jointCenterPiG