Implement GlobalCoPEvaluator in contact Component

[GiulioRomualdi]

This PR implements the GlobalZMPEvaluator class that can be used to compute the local and global ZMP given a set of contacts.

The class implements the same checks already in place in the walking-controller class. Such as:

• check for constant ZMP for a given amount of samples
• outlier rejection in the ZMP evaluation

I implemented also the associated python bindings

⚠️ I was not able to find a better name for the class so if you find something feel free to suggest it :)

[S-Dafarra]

Nitpick: the definition of the ZMP is slightly different, as it considers the acceleration of the CoM for example: see Eq. 21 of [1]. I think it would be more appropriate to use the CoP notation instead. The code of

bipedal-locomotion-framework/src/Contacts/src/Contact.cpp

Lines 45 to 47 in f7d9443

	zmp(0) = -wrench.torque()(1) / wrench.force()(2);
	zmp(1) = wrench.torque()(0) / wrench.force()(2);
	zmp(2) = 0.0;

corresponds to the definition of the CoP in case of planar ground. See Eq. (13) of [1]

[1]: Forces acting on a biped robot. Center of pressure-zero moment point

[GiulioRomualdi]

After discussing with @S-Dafarra we decided to use the term XoP instead of ZMP.

Still, one thing should be decided. Is GlobalCoPEvaluator the proper name or we can find something better?

[S-Dafarra]

Still, one thing should be decided. Is GlobalCoPEvaluator the proper name or we can find something better?

Maybe one thing to consider is to specify somewhere that by "global" we mean a weighted average, which may not follow the definition of "CoP"

[GiulioRomualdi]

Yes I'm going to explain this in the class documentation

[GiulioRomualdi]

Hi @S-Dafarra, I renamed the method from ZMP to CoP, let me know what you think :)

[S-Dafarra]

Minor comments

[traversaro]

Can you point to the formula used? I could not found the proposed formula in the paper.

[GiulioRomualdi]

Hi @traversaro it should be the following equation.

Still I can add the equation in the documentation

[traversaro]

But that is not the " weighted average of the CoP of each contact", right? This is the COP of the sum of the contact forces, and it can be proven that the two definitions are the same, with the assumptions that all the contacts occur in the same plane. So (nitpick) I would write "Consistently with", not "Following".

[GiulioRomualdi]

Here I wrote the math 881e92d

[traversaro]

Minor comments.

[S-Dafarra]

A small comment on the doc. Feel free to proceed

[GiulioRomualdi]

There was an uninitialized variable in GlobalCoPEvaluator::advance I fixed it in ba45836