How do I solve colcon build on Ubuntu?

Question

The error reads as follows:

By not providing "Findrosidl_default_generators.cmake" in CMAKE_MODULE_PATH
  this project has asked CMake to find a package configuration file provided
  by "rosidl_default_generators", but CMake did not find one.

  Could not find a package configuration file provided by
  "rosidl_default_generators" with any of the following names:

    rosidl_default_generatorsConfig.cmake
    rosidl_default_generators-config.cmake

Please, describe (list them in the question post) your steps for building the package. — Tsyvarev
Check where the cmake config script mentioned in the console output recides and specify the correct path in CMAKE_MODULE_PATH. Pretty much what the cmake output instructs you to do... — fabian
source /opt/ros/crystal/setup.bash and colcon build --merge-install --packages-skip individual_trajectories_bridge — Atul Joshi