OMPL planner changes the position of object after planning.

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Uli_v
Posts: 35
Joined: 14 Dec 2018, 18:07

OMPL planner changes the position of object after planning.

Post by Uli_v » 17 Jan 2019, 17:10

This post is related to my other post "Changing parent of object changes its position (by a small numerical error)". I decided to create this post, because the other post is mainly about the issue that changing the parent affects the position of the object. The other post is also much more detailed. This post is more about the OMPL planner (might) affect the position of the object after planning.

I am sharing a modified scene of "3DoFHolonomicPathPlanning.ttt":
https://drive.google.com/open?id=1tMgt- ... dBlTcSXSgR

The scene demonstrates the following issues:

- Changing the parents of "StartConfiguration" many times causes the position of the object to change. E.g. changing the parent 1000 times (to "no parent" and back to "Dummy") causes a positional error of 0.00046. The more iterations, the greater the error. To reproduce, enable child script of "Dummy" and disable child script of "StartConfiguration" and run the simulation.

- Running the OMPL path planner for "StartConfiguration" to find a 3D position path to "GoalConfiguration", also causes a positional error for "StartConfiguration" after planning. E.g. if planning for 10 seconds, the error is at least 0.04. To reproduce, disable child script of "Dummy" and enable child script of "StartConfiguration" and run the simulation.

What is special about this scene is that "StartConfiguration" has a parent ("Dummy") and the the rotations relative to world are not (0,0,0). I suspect that there is a calculation error for the position of "StartConfiguration" relative to its parent, either when the parent is changed, or when "StartConfiguration"'s position using global frame is changed (e.g. by the planner during collision checking).

Let me know what you think. Thank you.

Best,
Uli
Last edited by Uli_v on 18 Jan 2019, 17:16, edited 1 time in total.

coppelia
Site Admin
Posts: 7388
Joined: 14 Dec 2012, 00:25

Re: OMPL planner changes the position of object after planning.

Post by coppelia » 18 Jan 2019, 10:11

Hello Uli,

your link doesn't work..

Cheers

Uli_v
Posts: 35
Joined: 14 Dec 2018, 18:07

Re: OMPL planner changes the position of object after planning.

Post by Uli_v » 18 Jan 2019, 17:18

I fixed the link. Sorry about that.

coppelia
Site Admin
Posts: 7388
Joined: 14 Dec 2012, 00:25

Re: OMPL planner changes the position of object after planning.

Post by coppelia » 25 Jan 2019, 10:49

Hello again,

indeed, there can be a problem when an object has a parent, then reading its pose and setting it again leaves the object in a slightly different pose. We however couldn't observe drastic pose changes, even after thousands of iterations. In any case, we have modified the OMPL plugin, but that won't take effect until the next release (we also had to modify the V-REP library).
Thanks for pointing towards that problem. Linked to that issue is also the fact that calculations are currently in single precision (that's also on our todo list).

Cheers

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