Interpretation of values in the Transform6DVelocity IkParameterization

[Michael Koval]

Hi Rosen,

I'm trying to use the Transform6DVelocity IkParameterization to add
Cartesian velocities to an existing trajectory that contains
Transform6D ikparam_values group. The Transform6DVelocity group is,
surprisingly, 7-DOF. I'm not sure how to interpret these values
because I was expecting a 6-DOF twist. There also are not any helper
functions on the IkParameterization class to handle the conversion.

What are the values? How do I convert them to/from a twist?

Thanks,
-Michael

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[Chris Dellin]

Just a guess: are they position+quaternion derivatives?

- Chris

On Mon, Jun 30, 2014 at 5:22 PM, Michael Koval <[hidden email]> wrote:

Hi Rosen,

I'm trying to use the Transform6DVelocity IkParameterization to add
Cartesian velocities to an existing trajectory that contains
Transform6D ikparam_values group. The Transform6DVelocity group is,
surprisingly, 7-DOF. I'm not sure how to interpret these values
because I was expecting a 6-DOF twist. There also are not any helper
functions on the IkParameterization class to handle the conversion.

What are the values? How do I convert them to/from a twist?

Thanks,
-Michael

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Turn processes into business applications with Bonita BPM Community Edition
Quickly connect people, data, and systems into organized workflows
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[baxelrod]

I have also been hung up way too long on the proper format of what to pass into ikParameterization.  This could be documented A LOT better...  

Ben Axelrod
Sr. Robotics Software Engineer
iRobot Corporation
8 Crosby Drive, M/S 8-1
Bedford, MA 01730
[phone]
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________________________________________
From: Michael Koval [[hidden email]]
Sent: Monday, June 30, 2014 5:22 PM
To: [hidden email]
Subject: [OpenRAVE-users] Interpretation of values in the       Transform6DVelocity IkParameterization

Hi Rosen,

I'm trying to use the Transform6DVelocity IkParameterization to add
Cartesian velocities to an existing trajectory that contains
Transform6D ikparam_values group. The Transform6DVelocity group is,
surprisingly, 7-DOF. I'm not sure how to interpret these values
because I was expecting a 6-DOF twist. There also are not any helper
functions on the IkParameterization class to handle the conversion.

What are the values? How do I convert them to/from a twist?

Thanks,
-Michael

------------------------------------------------------------------------------
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Turn processes into business applications with Bonita BPM Community Edition
Quickly connect people, data, and systems into organized workflows
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[Rosen Diankov]

hi guys,

sorry for the late replies. you are right documentation is lacking, i've also had to look at how the code works internally several times to remind me ;0)

in any case Transform6DVelocity is derivative of the quaterion (first 4 values), derivative of the translation (next 3 values).

in the master branch (just committed), i've added  GetIkParameterization(IKP_Transform6DVelocity) to return an ikparameterization velocity of the manipulator tooltip depending on the end effector link velocity coming from the dof velocities.

Vector vlinearvel, vangularvel;
GetEndEffector()->GetVelocity(vlinearvel, vangularvel);

Transform tee = GetTransform();
vlinearvel += vangularvel.cross(tee.trans - GetEndEffector()->GetTransform().trans);

Transform tvel;
tvel.trans = vlinearvel;
tvel.rot = quatMultiply(t.rot,Vector(0,vangularvel.x,vangularvel.y,vangularvel.z)) * 0.5;
ikp.SetTransform6DVelocity(tvel);

Note how the derivative of a quaterion q(t)  is:

q'(t) = 0.5* q(t) * Quaternion(0, angularvelocity.x, angularvelocity.y, angularvelocity.z)

hope this helps,

rosen,

2014-07-01 9:00 GMT+09:00 Axelrod, Ben <[hidden email]>:

I have also been hung up way too long on the proper format of what to pass into ikParameterization.  This could be documented A LOT better...

Ben Axelrod
Sr. Robotics Software Engineer
iRobot Corporation
8 Crosby Drive, M/S 8-1
Bedford, MA 01730
<a href="tel:%28781%29%20430-3315" value="[phone]">[phone]
[hidden email]

________________________________________
From: Michael Koval [[hidden email]]
Sent: Monday, June 30, 2014 5:22 PM
To: [hidden email]
Subject: [OpenRAVE-users] Interpretation of values in the       Transform6DVelocity IkParameterization

Hi Rosen,

I'm trying to use the Transform6DVelocity IkParameterization to add
Cartesian velocities to an existing trajectory that contains
Transform6D ikparam_values group. The Transform6DVelocity group is,
surprisingly, 7-DOF. I'm not sure how to interpret these values
because I was expecting a 6-DOF twist. There also are not any helper
functions on the IkParameterization class to handle the conversion.

What are the values? How do I convert them to/from a twist?

Thanks,
-Michael

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Turn processes into business applications with Bonita BPM Community Edition
Quickly connect people, data, and systems into organized workflows
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