Tiziano/build linear system

[tizianoGuadagnino]

Reach branch name a.k.a expose the linear system construction in the optimization loop. Allows to compute the covariance of the estimate and use the KISS-ICP code for other tasks (LIO etc).

[nachovizzo]

@tizianoGuadagnino this looks good to me. But for next time is better if we go through a round of reviews before merging this tho the main branch immediately.

1. Since this is not even mentioned in the paper should we at least add some comments?
2. Why you have not exposed this to the python API, the ROS wrappers etc 🤔? This now diverged from the original way of implementing new features

[tizianoGuadagnino]

@nachovizzo there is no difference with what was there before, even less difference with the paper because we never mention exponential and logarithmic mapping in the alignment part...

The RegisterFrame function has been simply splitted in two, I'm happy to revert it if that breaks the flow of the development.

How should I expose it in the ROS wrapper ? please explain. I'm happy to pybinded if that is critical.

I follow the policy "It is a small change for now I merge it, I'm happy to revert it later" cit someone

[nachovizzo]

@tizianoGuadagnino Honestly I haven't reviewed the changes thoroughly :D

Now I see that API hasn't been changed (GitHub diff is not helping with this). But since you opened a new version I assumed you were messing around with the API (check https://semver.org/)

Since the API didn't change I wouldn't bump a new version, and if the BuildLinearSystem function is not exposed then I will keep it an unnamed namespace within the translation unit....

If it requires to be exposed, then that's what would be maybe interesting to expose to Python and ROS