questions on descarte planning, meaning of orient_increment

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Hey all,

I wonder what is the meaning of orient_increment in AxialSymmetricPt? On its class reference, it shows

> orient_increment  (in radians, discretization of space [-Pi, Pi])

But what does discretization mean here? My understanding is that it discretize [-Pi,Pi], like [-pi, -pi+0.01,-pi+0.02,....,pi-0.01,pi]. Is this right?

I was following the descarte tutorial, it used this helper function

descartes_core::TrajectoryPtPtr makeTolerancedCartesianPoint(const Eigen::Affine3d& pose)
{
    using namespace descartes_core;
    using namespace descartes_trajectory;
  return TrajectoryPtPtr( new AxialSymmetricPt(pose, // Nominal pose
                                               M_PI/2.0, // Search discretization
                                               AxialSymmetricPt::Z_AXIS) ); // Free axis
}

I wonder what does the M_PI/2 means.

Any help would be deeply appreciated.