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questions on descarte planning, meaning of orient_increment

asked 2017-07-05 22:54:35 -0500

thompson104 gravatar image

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.

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answered 2017-07-06 09:11:15 -0500

BrettHemes gravatar image

You are correct in your thinking. In the cited example the discretization is specified as increments of pi/2 (90 degrees). M_PI is a constant for pi from the math library math.h

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Thank you for your reply. I'm kind of curious why is pi/2 is enough? Does pi/2 apply to the joints?

thompson104 gravatar image thompson104  ( 2017-07-06 11:13:00 -0500 )edit

Pi/2 is arbitrary in this case and in my experience not enough. This is the discretization about the specified free axis in terms of tool/frame poses (i.e., Cartesian and not joint angles). Ultimately it is a trade-off between search resolution and planning time.

BrettHemes gravatar image BrettHemes  ( 2017-07-06 11:37:12 -0500 )edit

I usually start with pi/16 and adjust from there but it will be application dependant in the end

BrettHemes gravatar image BrettHemes  ( 2017-07-06 11:38:15 -0500 )edit

Thank you. I'm going to try it with different values to see what's the difference. Thank you for your reply.

Also, I wonder if you know some moveit examples with good documents available?

thompson104 gravatar image thompson104  ( 2017-07-06 11:56:27 -0500 )edit

For just moveit there are good ones on their wiki here. For Descartes, there is less. You can start here

BrettHemes gravatar image BrettHemes  ( 2017-07-06 15:47:47 -0500 )edit

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Asked: 2017-07-05 22:54:35 -0500

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Last updated: Jul 06 '17