cartographer

Want to contribute? Great! Make sure you've checked all these boxes before creating your PR:

Keep your PR rebased to master.
Keep your PR under 200 lines of code and address a single concern.
Add unit test(s) and documentation (these do not count toward your 200 lines).
Adhere to the Google C++ Style Guide.
Run clang-format -style=Google on your code (this alone is not enough to ensure you've followed the style guide).
Run ninja test or catkin_make_isolated --install --use-ninja --pkg cartographer --make-args test as appropriate.