def _get_epe(self, kp_id):
    ' Returns end point error for one keypoint. '
    if (len(self.data[kp_id]) == 0):
        return (None, None)
    data = np.array(self.data[kp_id])
    epe_mean = np.mean(data)
    epe_median = np.median(data)
    return (epe_mean, epe_median)
Returns end point error for one keypoint.
def _get_epe(self, kp_id):
    '  '
    if (len(self.data[kp_id]) == 0):
        return (None, None)
    data = np.array(self.data[kp_id])
    epe_mean = np.mean(data)
    epe_median = np.median(data)
    return (epe_mean, epe_median)