CGAL/Eigen Conversion Adapters to streamline interfaces

michaelpantic commented 5 years ago

More PRs! Sorry :-) Warning: Code in this PR is made highly generic and solves a very technical problem but will increase code readability for other functions a lot. Code readability of this part though...well I tried my best.

Content of PR: Custom data type that allows us to write functions that consume/return cgal::Vector/Eigen::Vector3d/cgal::Point at the same time without ever having to explicitly convert/cast. Same applies for cgal::Vector_2/Eigen::Vector2d/cgal::Point_2, depending on template parameter N.

This PR can be merged independently of the others.

See following code comment and/or tests in file test_cgal_eigen_adapter.cpp for example.

Text from code comment:

This header-only library provides functionality to design functions such that they automatically accept eigen and cgal vectors without templates/overloading and the like. Makes Eigen::Vector3d / cgal::Vector_3 / cgal::Point_3 interchangeable.

Examples:

You want a function that accepts a Vector3 (regardless of eigen/cgal):
- Signature:void yourFunction(Vector3In vec)
- Usage: Whenever you assign vec to a cgal or eigen vector, it gets converted transparently.
- Inside the function: e.g. Eigen::Vector3d test = vec; or cgal::Vector test2 = vec;
- Calling the function: yourFunction(test) (where test is of type Eigen::Vector3d o cgal::Vector/Point, doesn't matter)
- You want a function that returns a Vector3 that can be assigned to eigen / cgal:
- Signature: Vector3Return yourFunction()
- Usage: Eigen::Vector3d test = yourFunction(); or cgal::Vector test2 = yourFunction();
- Inside function: return Eigen::Vector3d(...) or cgal::Vector(...) or cgal::Point(...)
You want a function with a Vector3 as output parameter:
- Signature:void yourFunction(Vector3Out vec_out)
- Usage inside function: Just assign a eigen/cgal vector to vec_out
- Calling function: yourFunction(&test), where test is of type Eigen::Vector3d or cgal::Vector or cgal::Point)

Of course any combination of the above 3 is also valid.

Example from code: See public methods from e.g. https://github.com/ethz-asl/cad-percept/blob/9215a98a04d1ea2d3618a6ad773060548b2b913a/cpt_planning/include/cpt_planning/coordinates/barycentric.h#L15

Defines barycentric coordinates for 2d and 3d types and allows usage and return of any mixture of cgal/eigen types with only 4 methods defined !