Filter transitions - Githubissues

humanoid-path-planner / hpp-manipulation-corba

Corba server for manipulation planning

BSD 2-Clause "Simplified" License

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Filter transitions #98

Closed florent-lamiraux closed 4 years ago

florent-lamiraux commented 4 years ago

https://github.com/humanoid-path-planner/hpp-manipulation-corba/blob/2f1c5592ac21218c377fd008f79adf14518569fa/src/hpp/corbaserver/manipulation/constraint_graph_factory.py#L296 I think we should add a call to a new method called "transitionIsAllowed" here to filter out transitions where an object moves without being grasps. This happens when stacking boxes equipped with grippers and handles.

jmirabel commented 4 years ago

We already planned paths for scenarios with objects (like a tool) with grippers and handles. We always managed to generate the graph using rules (I think, but we may also have modified the generated graph).

Out of curiosity, what is the case that requires you to add this function ?

florent-lamiraux commented 4 years ago

The use case is a forklift that is required to stack boxes on top of each other.

box2 is put on box1 using gripper "box1/top" and handle "box2/bottom".
The boxes are placed on the ground using contact surfaces. State "box1/top grasps box2/bottom" is allowed. It corresponds to box1 put on the ground and box2 put on box1. The factory builds a transition between "free" and this latter state although box2 cannot climb on box1 by itself. This type of situation may certainly be detected automatically.

jmirabel commented 4 years ago

Then, there is a bug in the Python factory. Normally, an object that is not grasped cannot be moved so box1 should not be movable.

florent-lamiraux commented 4 years ago

I would not call that a bug. Method ConstraintGraphFactory._recurse does not make any difference between objects and robots. As it is implemented now, it requests "box1/top" to grasp "box2/bottom" without realizing that "box1" is an object.

jmirabel commented 4 years ago

After an oral discussion, the problem is that the graph contains infeasible transition (they are truly infeasible) rather that not generating them.

florent-lamiraux commented 4 years ago

Solved by https://github.com/humanoid-path-planner/hpp-manipulation-corba/pull/99.