Add eigen support

[PepMS]

As discussed in #66 , this PR adds the possibility to log Eigen::VectorXd objects.

Adding Eigen compatibility is configurable through cmake variables and the use of preprocessor directives inside the code.

[MaximilienNaveau]

Hi @PepMS, how are you doing?

Thank you very much for this PR, it's really helpful.

I have my 2 cents comment on this work.
I would believe that using the ground rules for Eigen for passing Eigen object into functions would be beneficial here.
Either using templates or Eigen::Ref.

See: https://libeigen.gitlab.io/eigen/docs-5.0/TopicFunctionTakingEigenTypes.html

My comment applies for the full PR.

[MaximilienNaveau]

@PepMS any plans on continuing this PR?

[PepMS]

@MaximilienNaveau yes, indeed. Sorry for not having done this before. I'll try to allocate some time to continue that during this week.

[PepMS]

I just pushed my changes @MaximilienNaveau. Here's a recap

• I used the templated approach — see values.hpp. It adds support for Eigen::Matrix and Eigen::Array objects, both fixed and dynamic size.
• I added a static_assert restricting it to vector-like types. Matrices could be supported too, but then we would have no information about the ordering of the elements.
• I explicitly reject registering views and expressions (blocks, maps, refs).
• I added tests in tests/eigen_tests.cpp: schema shape for fixed vs dynamic size, a round-trip through the parser, a dynamic vector resized between snapshots, and parity with the equivalent std::array / std::vector.

This PR has been developed with the support of Claude.

[MaximilienNaveau]

Some packaging issue at first glance,
@henrygerardmoore as you are targeted as the main reviewer, could you start the CI so we see the sanity?

[MaximilienNaveau]

is IsEigenType<> defined is the Eigen include is not loaded?

[PepMS]

IsEigenType<> evaluates to true whenever the type T is an object from the Eigen library. Otherwise is false.

If Eigen is not included IsEigenType defaults to false.

Here: https://github.com/PickNikRobotics/data_tamer/pull/67/changes/BASE..73fedd4e9c1f30df781fc964339cf8d91f9d2217#diff-d7946cad3c50605c63a784c0197e38a8e5fee1901efe4290f3514a062c7837bbR33

[MaximilienNaveau]

I missed it!
Sorry for that!!

[MaximilienNaveau]

Good job but see below the option to mcap make the package.xml needing the mcap_vendor as well as a dependency.

Hence you need to add Eigen to the package.xml as well. And you need to update the conanfile.py as well to declare eigen3 there as well. Pick the version of Eigen that is default on the lowest version of the OS. i.e. ros2 humble meaning Ubunut22.04. I will let you find the proper Eigen version for this.

[MaximilienNaveau]

An additional comment here, we would need a CI that build with/without the different options.
Maybe it's a bit brute force and you actually set the option to ON by default so I guess it's ok, but did you try to build with the option OFF on a fresh build?