Update documentation, clean up rviz plugin CMakeLists (#302)

- Among the lines added in #150, the one that fixes building with Qt5 is
  the following line:

  include_directories(${Qt5Widgets_INCLUDE_DIRS})

  The rest is redundant and actually doesn't do anything. A CMake
  variable named QtX_INCLUDE_DIRS is not defined when find_package()-ing
  Qt. Also, there is no need to find_package() Qt5 Widgets twice.

- In documentation, add sudo to rosdep init invocation, following
  http://wiki.ros.org/rosdep. Add a comment about the error which will
  be printed if the user has already run sudo rosdep init since
  installing ROS.

cartographer_rviz/CMakeLists.txt

@@ -48,15 +48,12 @@ target_link_libraries(${PROJECT_NAME} PUBLIC ${QT_LIBRARIES})
 if(rviz_QT_VERSION VERSION_LESS "5")
   message(STATUS "Using Qt4 based on the rviz_QT_VERSION: ${rviz_QT_VERSION}")
   find_package(Qt4 ${rviz_QT_VERSION} EXACT REQUIRED QtCore QtGui)
-  include_directories(${Qt4_INCLUDE_DIRS})
   include(${QT_USE_FILE})
 else()
   message(STATUS "Using Qt5 based on the rviz_QT_VERSION: ${rviz_QT_VERSION}")
   find_package(Qt5 ${rviz_QT_VERSION} EXACT REQUIRED Core Widgets)
-  find_package(Qt5Widgets REQUIRED)
   set(QT_LIBRARIES Qt5::Widgets)
   include_directories(${Qt5Widgets_INCLUDE_DIRS})
-  include_directories(${Qt5_INCLUDE_DIRS})
 endif()
 add_definitions(-DQT_NO_KEYWORDS)
 

docs/source/index.rst

@@ -67,7 +67,9 @@ We recommend using `wstool <http://wiki.ros.org/wstool>`_ and `rosdep
     wstool update -t src
 
     # Install deb dependencies.
-    rosdep init
+    # The command 'sudo rosdep init' will print an error if you have already
+    # executed it since installing ROS. This error can be ignored.
+    sudo rosdep init
     rosdep update
     rosdep install --from-paths src --ignore-src --rosdistro=${ROS_DISTRO} -y