Adding position constraint with slack

[Andrew Hundt]

I'm planning to add a position based constraint with a configurable amount of slack permitted.
Is something similar to this covered by objects like MotionConstr? The docs are a bit sparse in that file.

Additionally, is there any relevant advice or limitations I should know before I create the changes?

[Hervé Audren]

Depending on what you want to do, there might be some way to do it already:

• If you want to add a position constraint, using a ContactConstr is actually probably the way to go, it doesn't matter if this contact can produce contact forces or not. By using a DofContact and possibly a PositionTask, you can have a moving contact, blocked in some DoF, and moving in others. However, you cannot be strict on the range allowed.
• If you want to be able to strictly move in some workspace, then I would recommend to implement a new BodyInPlaneConstr, based on ComIncPlaneConstr. This constraint allows to constraint the CoM to a convex region defined by its hyperplanes (i.e. inequalities), you would basically need to replace CoM position by bodyPosW[i] and CoMJacobian by a regualr Jacobian.
• If you really want to add a PositionConstr with some slack allowed, we would need to modify the underlying structure of the solver to allow for easy adding/removal of variables. It is possible for now, but definitely not practical.

Cheers,