[SOLVED] Access constraint forces from a different class

[Times]

Hi guys,

I would like to get the constraint forces from the GenericConstraintSolver and pass them to my class but I have not been able to do so as all I get are zero/null values.

The address of the constraint forces can be retrieved within the GenericConstraintSolver class by current_cp->GetF();

How can I go about doing this outside the GenericConstraintSolver? Any help/ideas would be appreciated. Thanks.

[Hugo]

Hey @akthetimes

From what I see you are attempting to do this in C++. Correct?

The GenericConstraintSolver has two dedicated options to compute the constraint forces:
– computeConstraintForces: boolean enablin the storage of the constraintForces
– constraintForces: vector containing the constraint forces

The type of constraintForces is type::vector< double >, make sure you are accessing it properly (WriteAccessor) and that you use the proper data type.

Since both are SOFA data, you can access them from outside the GenericConstraintSover.
Do you see my point?
Do you have a code snippet on your end that we could edit?

Best

Hugo

[Times]

Hey @Hugo,
Thanks for the reply! For example if we’d like to print out the values of the constraint forces from another class.

sofa::component::constraintset::GenericConstraintSolver* solver;
Data<type::vector< double >> constraintForces = solver->d_constraintForces.getValue();

if (condition)
msg_info("Constraint Forces") << constraintForces;

How could I go about this?

[Hugo]

Ok then you could write something like:

sofa::component::constraintset::GenericConstraintSolver* solver;
type::vector< double > constraintForces = solver->d_constraintForces.getValue();

if (condition)
msg_info("Constraint Forces") << constraintForces;

Keep us posted if this helps.
How do you get the pointer to the GenericConstraintSolver?

Best,

Hugo

[Times]

@Hugo, that perhaps is my question. How do I get the pointer to the GenericConstraintSolver?

[Hugo]

Hey @akthetimes

This depends on where/what is your code supposed to be implemented?
What is this C++ code you want to write?

Best

Hugo

[Times]

Hey @Hugo,

I would like to impose different constraints depending on the contact force. So for example, in the SOFA class FrictionContact(FrictionContact -SOFA API), in the createResponse function, I’d like to reference the ConstraintSolver so I can impose a contact depending on the force. I appreciate any help you can offer on this. Thanks

[Times]

I was able to solve it like this:

 core::objectmodel::BaseContext* context = this->getContext();
  context->get(constraintSolver); 

and finally the constraint forces can be printed out:
msg_info("constraint forces") << constraintSolver->getConstraintProblem()->f;

[Hugo]

Great @akthetimes

All my apologies for the delay!
Thanks for closing the topic, do not hesitate to keep us updated!

Best

Hugo

[Author]

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