How does on include the PCL library to an existing ros package code?

edit

I am trying to convert my code from using a vector of particles to a proper point cloud implementation. I want to use the octree module of PCL for radius based searches. However, when compiling the code, I get undefined references to Octree library functions.

I am using Ubuntu 18.04.3 LTS with ROS-melodic. I tried including PCL-1.8 under /usr/include in my CMakeLists.txt file as well as downloading and adding PCL-1.9.1 under my ros package (which crashes my PC during compilation). I am also not able to find_package() the pcl library.

Any help would be greatly appreciated.

cmake_minimum_required(VERSION 2.8.3)
project(points_reader)

add_compile_options(-std=c++17)

set(${PROJECT_NAME}_DEPS
  dynamic_reconfigure
  message_runtime
  roscpp
  rospy
  toposens_pointcloud
  toposens_driver
  toposens_msgs
  tf
  # pcl
  pcl_conversions
  pcl_ros
  sensor_msgs
)

find_package(
  catkin REQUIRED
  COMPONENTS ${${PROJECT_NAME}_DEPS}
)

############
## Config ##
############

catkin_package(
  INCLUDE_DIRS include
  LIBRARIES ${PROJECT_NAME}
  CATKIN_DEPENDS ${${PROJECT_NAME}_DEPS}
)

################
## Executable ##
################

add_subdirectory(external/pcl)

include_directories(${PCL_INCLUDE_DIRS})
link_directories(${PCL_LIBRARY_DIRS})
add_definitions(${PCL_DEFINITIONS})

include_directories(
  include 
  external
  ${catkin_INCLUDE_DIRS}
)

add_library(
  ${PROJECT_NAME}
  src/line.cpp
  src/fitness_evaluator.cpp
  src/points_reader.cpp
  src/points_mapper.cpp
  src/bounding_box.cpp
  src/points_publisher.cpp
)

add_dependencies(
  ${PROJECT_NAME}
  # ${PROJECT_NAME}_gencfg
  ${catkin_EXPORTED_TARGETS}
)

add_executable(
  ${PROJECT_NAME}_node
  src/points_reader_node.cpp
)

target_link_libraries(
  ${PROJECT_NAME}_node
  ${PROJECT_NAME}
  ${catkin_LIBRARIES}
  ${PCL_LIBRARIES}
)

install(
  TARGETS ${PROJECT_NAME}_node
  RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
  COMPONENT main
)

##########
## Test ##
##########

if(CATKIN_ENABLE_TESTING)
  add_subdirectory(tests)
endif()