I'm using ubuntu bionic that has assimp 4.1.0. As a result rviz_assimp_vendor doesnt build the assimp from source.

CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
library_abs
    linked by target "rviz_rendering" in directory /root/ros2/ros2_ws/src/ros2/rviz/rviz_rendering

I narrowed it down to assimp exporting the wrong library dirs:
ASSIMP_LIBRARY_DIRS:/usr/lib/lib/x86_64-linux-gnu

It seems to not be handling the architecture specific dir properly and duplicate the "lib" in the provided path. So I guess we would need to convince either assimp devs or debian assimp maintainers to use GNUInstallDirs

/cc @wjwwood as maintainer
/cc @nuclearsandwich as the person wit hthe most experience with GNUInstallDirs

Edit: Actually they are using GNUInstallDirs. Didn't look further into it, likely just a tweak to the generated Config file.
What worked for me (though I'm not sure that's the "right" solution: mikaelarguedas/assimp@a440713

Before the hack:

-- ASSIMP_LIBRARY_DIRS:/usr/lib/lib/x86_64-linux-gnu
-- ASSIMP_ROOT_DIR:/usr/lib
-- ASSIMP_INCLUDE_DIRS:/usr/lib/include

After the hack:

-- ASSIMP_LIBRARY_DIRS:/usr/lib/x86_64-linux-gnu
-- ASSIMP_ROOT_DIR:/usr
-- ASSIMP_INCLUDE_DIRS:/usr/include