motionPlanningDemo1 distance measure

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kurtserP
Posts: 2
Joined: 06 Jul 2017, 16:16

motionPlanningDemo1 distance measure

Postby kurtserP » 06 Jul 2017, 18:32

I'm trying to understand the mening of the distance measure between configurations and as function of a metric.
As presented in motionPlanningDemo1:

Code: Select all

x=(config1[i]-config2[i])*metric[i]


This implied that the distance is a distance of angles multiplied by a metric, but what does the metric represents? The length of the joint? Why is that then linear?

I would appreciate an example.
Thank you

coppelia
Site Admin
Posts: 6058
Joined: 14 Dec 2012, 00:25

Re: motionPlanningDemo1 distance measure

Postby coppelia » 06 Jul 2017, 19:58

Hello,

imagine a robot in configuration A, a robot in configuration B, and a robot in configuration C. We want to know which is shorter: move from A to B, or to move from A to C? In order to answer that question, we somehow need to be able to measure a distance between 2 configurations? do we simply square all joint angles, add them, then extract the square root? And what happens if we have linear and angular actuators? Is one radian equivalent to 1 meter (in terms of distance)? A distance metric allows to help answer above questions. The way the metric is defined depends on the task, the robot, etc.

Cheers

kurtserP
Posts: 2
Joined: 06 Jul 2017, 16:16

Re: motionPlanningDemo1 distance measure

Postby kurtserP » 08 Jul 2017, 18:05

Dear coppelia,
Thank you for your quick and full answer.
Is there any meaning to the number that are currently there in the demo?

coppelia
Site Admin
Posts: 6058
Joined: 14 Dec 2012, 00:25

Re: motionPlanningDemo1 distance measure

Postby coppelia » 10 Jul 2017, 09:57

Actually yes, but this really depends on your robot and application. In a serial manipulator for instance, you usually want to give more weight to the base joints, since a displacement of them can cause a large displacement of the end-effector.

Cheers


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