Gazebo extra installation steps on Ubuntu 20.04 about revolve

[surgura]

Thank you for reporting. I will do another installation pass on a clean Ubuntu 20.04 and see if I reproduce & update the docs

[soudy]

Some other gotcha's I encountered while installing that might save others some debugging:

1. Had to install nlopt from source (https://github.com/stevengj/nlopt). Package libnlopt-dev in Ubuntu 20.04 repo didn't get recognized correctly by CMake somehow.
2. libyaml-cpp-dev from repo has a pathing error: in /usr/lib/x86_64-linux-gnu/cmake/yaml-cpp/yaml-cpp-config.cmake YAML_CPP_INCLUDE_DIR is set to "${YAML_CPP_CMAKE_DIR}/../../../../../include", which is one directory too high and caused errors. Fixed by settings YAML_CPP_INCLUDE_DIR to "${YAML_CPP_CMAKE_DIR}/../../../../include" (one ../ removed so it points correctly at /usr/include).

[surgura]

hmm weird. My experience is that libnlop-dev is enough. Same for yaml. I'm also running 20.04 without any problems with a fresh revolve installation from last month. Oh well, I'll do a cleanup of dependencies soon to hopefully resolve these issues.

[surgura]

Correction I run 20.10

[soudy]

I should have maybe noted that this is on Babak's fork https://github.com/bobykhani/revolve on the LinearActuator branch. I tried using the CMake files from this repo's master branch, however it wasn't a mistake in the CMake files but in the system libraries setup. Could be some slight versioning difference between 20.04 and 20.10 that messes some things up, I'm not sure.