Trying to understand joint1_placement.setRandom() and joint1_placement.setIdentity() in Pinocchio 3 RigidConstraintModel

[zixinz990]

I am trying to calculate the constrained forward dynamics of a humanoid robot. The only two constraints are that both feet must be fixed to the ground. I found that Pinocchio 3 seems to have some functions I need.

I am reading the unit test code for constraint dynamics in Pinocchio 3. I am confused by the way the developer initializes the constraints. In test_sparse_forward_dynamics_in_contact_6D_LOCAL, which is in unittest/constrained-dynamics.cpp, they define the constraints like this:

PINOCCHIO_STD_VECTOR_WITH_EIGEN_ALLOCATOR(RigidConstraintModel) contact_models;
PINOCCHIO_STD_VECTOR_WITH_EIGEN_ALLOCATOR(RigidConstraintData) contact_datas;

RigidConstraintModel ci_RF(CONTACT_6D,model.getJointId(RF),LOCAL);
ci_RF.joint1_placement.setRandom();
contact_models.push_back(ci_RF);
contact_datas.push_back(RigidConstraintData(ci_RF));

RigidConstraintModel ci_LF(CONTACT_6D,model.getJointId(LF),LOCAL);
ci_LF.joint1_placement.setRandom();
contact_models.push_back(ci_LF);
contact_datas.push_back(RigidConstraintData(ci_LF));

I am not sure what does ci_RF.joint1_placement.setRandom() and ci_LF.joint1_placement.setRandom() mean here. I also noticed that there is another function setIdentity() which sets some transformation to identity. I was also wondering how to set constraints for the feet in my case.