How do I include the header?

edit

I am currently having some problem including header within my catkin_package.

This is the file structure:

pkg_a/
├── CMakeLists.txt
├── CMakeLists.txt.user
├── include
│   └── pkg_a
│       ├── pugiconfig.hpp
│       └── pugixml.hpp
├── package.xml
├── src
     ├── src.cpp
     ├── header_to_src.h
     ├── node.cpp
     ├── pugixml.cpp
     ├── src_2.cpp
     └── header_to_src_2.h

I am trying to include pugixml.hpp in the cpp. file. The way i've tried to do it is like this

 #include <pkg_a/pugixml.hpp>

But it cannot find it.. What is the path to it.. I would like to avoid making direct path to the include folder, such that other packages also easily can enter include the .hpp file.

This is the CMakeList

cmake_minimum_required(VERSION 2.8.3)
project(pkg_a)

#Compiler flags
add_definitions(-std=c++1y)
find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
  genmsg
  message_generation
  depend_1
  depend_2
)


catkin_package(
   INCLUDE_DIRS include
   LIBRARIES ${PROJECT_NAME}
   CATKIN_DEPENDS
   DEPENDS system_lib

)

include_directories(
  include
  ${catkin_INCLUDE_DIRS}
)

## Mark cpp header files for installation
 install(DIRECTORY include/${PROJECT_NAME}/
   DESTINATION ${CATKIN_PACKAGE_INCLUDE_DESTINATION}
   FILES_MATCHING PATTERN "*.h" PATTERN "*.hpp"
   PATTERN ".svn" EXCLUDE
 )

## Mark other files for installation (e.g. launch and bag files, etc.)
 install(
     DIRECTORY include/${PROJECT_NAME}/
#   # myfile1
#   # myfile2
   DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}
 )

SET(SRC_FILES
        ${SRC_FILES}
        ${CMAKE_CURRENT_SOURCE_DIR}/src/src.cpp
        ${CMAKE_CURRENT_SOURCE_DIR}/src/src_2.cpp
        ${CMAKE_CURRENT_SOURCE_DIR}/src/pugixml.cpp
#       ${CMAKE_CURRENT_SOURCE_DIR}/src/main.cpp
        CACHE INTERNAL ""
)

add_library(${PROJECT_NAME} ${SRC_FILES})

add_executable(run_${PROJECT_NAME} ${CMAKE_CURRENT_SOURCE_DIR}/src/node.cpp ${CMAKE_CURRENT_SOURCE_DIR}/src/pugixml.cpp)
add_dependencies( ${PROJECT_NAME} depend_1_generate_messages_cpp depend_2_generate_message_cpp )
target_link_libraries(run_${PROJECT_NAME}
    ${PROJECT_NAME}
    ${catkin_LIBRARIES}
)