CMake OpenCV 3.0.0 and building executables and libraries in Ubuntu - opencv

Question

I have OpenCV 3.0.0 installed in /usr/local/opencv-3.0.0
I am trying to construct a CMakeLists file to build a library against this OpenCV 3.0.0. The CMakeLists.txt is as follows:
cmake_minimum_required(VERSION 2.8)
project(STT_People_Tracker)
cmake_policy(SET CMP0016 NEW)
# compilation mode setup
#set(CMAKE_BUILD_TYPE Release)
set(CMAKE_BUILD_TYPE Debug)
# set OpenCV directories - CHANGE DEPENDING ON SYSTEM
set(OpenCV_PATH "/usr/local/opencv-3.0.0")
set(OpenCV_INCLUDE_DIRS "${OpenCV_PATH}/include")
set(OpenCV_LIBS "${OpenCV_PATH}/lib/")
# set environment variables
set(SOURCES_PATH "${CMAKE_SOURCE_DIR}/Sources")
set(INCLUDES_PATH "${SOURCES_PATH}/include")
if(CMAKE_BUILD_TYPE MATCHES Debug)
set(OUTPUT_PATH "../Debug")
message(STATUS "Compiling in DEBUG mode")
elseif(CMAKE_BUILD_TYPE MATCHES Release)
set(OUTPUT_PATH "../Release")
message(STATUS "Compiling in RELEASE mode")
endif()
include_directories(${INCLUDES_PATH})
include_directories(${OpenCV_INCLUDE_DIRS})
# compilation of executables
message(STATUS "configuring executables...")
add_executable(${OUTPUT_PATH}/mainTest ${SOURCES_PATH}/mainTest.cpp)
# compilation of libraries
message(STATUS "configuring libraries...")
add_library(${OUTPUT_PATH}/background_substractor ${SOURCES_PATH}/background_substractor.cpp)
# set linker options
link_directories(${OpenCV_LIBS})
target_link_libraries(${OUTPUT_PATH}/mainTest opencv_core opencv_highgui)
target_link_libraries(${OUTPUT_PATH}/background_substractor opencv_core opencv_highgui)
message(STATUS "cmake configuration complete")
It is a fairly simple Cmake file, however, I have the following problems/doubts:
1.-How can I know I am using OpenCV 3, and not other versions of OpenCV present in the system?
2.- When compiling the file background_substractor, its associated header file can not be located, although I have checked the path and it is correctly assigned in the set(INCLUDES_PATH "${SOURCES_PATH}/include"):
/home/alberto/STT_People_Tracking/Sources/background_substractor.cpp:3:36: fatal error: background_substractor.h: No such file or directory
#include "background_substractor.h"
^
compilation terminated.
make[2]: *** [CMakeFiles/../Debug/background_substractor.dir/Sources/background_substractor.cpp.o] Error 1
make[1]: *** [CMakeFiles/../Debug/background_substractor.dir/all] Error 2
make: *** [all] Error 2
3.- Finally, and if I comment the header file, I have problems linking:
Linking CXX static library lib../Debug/background_substractor.a
/usr/bin/ar: lib../Debug/background_substractor.a: No such file or directory
make[2]: *** [lib../Debug/background_substractor.a] Error 1
make[1]: *** [CMakeFiles/../Debug/background_substractor.dir/all] Error 2
make: *** [all] Error 2
I have tried everything: Specifying the include files in the add_executable() and add_library() commands, I have checked paths and they are ok, etc etc.
Could anyone more experienced with CMake, give me a little hand?
Thank you very much in advance,
Alberto

Answer 1

How can I know I am using OpenCV 3, and not other versions of OpenCV present in the system?
Your project should check that.
But usually projects just use find_package command for fill variables related to 3d-party library. This command perform all needed checks. In your case it could be
find_package(OpenCV 3 REQUIRED)
call, which fills OpenCV_LIBS and OpenCV_INCLUDE_DIRS variables automatically. This command, by default, search OpenCV installation in default paths, but you can adjust searching algorithm by using parameters to cmake (so, you needn't to change CMakeLists.txt when you build the project on other machine). E.g., this way
cmake -DOpenCV_DIR=/usr/local/opencv-3.0.0 <source-dir>
you can specify precise installation path of OpenCV.
When compiling the file background_substractor, its associated header file can not be located...
Cannot suggest anything aside from checking file existence
/home/alberto/STT_People_Tracking/Sources/include/background_substractor.h
But this also can be a result of the 3d issue(see below).
Finally, and if I comment the header file, I have problems linking...
Your usage of CMake targets is incorrect. Unlike to make targets, which usually are files, CMake targets are simple names. By default, name of library/executable target determines filename of the library/executable file, produced by this target, but this can be changed. Directory, where resulted file will be located, can be adjusted using CMAKE_<TYPE>_OUTPUT_DIRECTORY variables, where <TYPE> can be ARCHIVE, LIBRARY or RUNTIME depending on target type.
Correct CMake script would be:
cmake_minimum_required(VERSION 2.8)
project(STT_People_Tracker)
cmake_policy(SET CMP0016 NEW)
# compilation mode setup
#set(CMAKE_BUILD_TYPE Release)
set(CMAKE_BUILD_TYPE Debug)
# set OpenCV directories using find_package.
find_package(OpenCV 3 REQUIRED)
# set environment variables
set(SOURCES_PATH "${CMAKE_SOURCE_DIR}/Sources")
set(INCLUDES_PATH "${SOURCES_PATH}/include")
if(CMAKE_BUILD_TYPE MATCHES Debug)
set(OUTPUT_PATH "${CMAKE_BINARY_DIR}/Debug") # Use absolute path
message(STATUS "Compiling in DEBUG mode")
elseif(CMAKE_BUILD_TYPE MATCHES Release)
set(OUTPUT_PATH "${CMAKE_BINARY_DIR}/Release")
message(STATUS "Compiling in RELEASE mode")
endif()
# Set output directory for STATIC libraries and executables
set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${OUTPUT_PATH})
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${OUTPUT_PATH})
include_directories(${INCLUDES_PATH})
include_directories(${OpenCV_INCLUDE_DIRS})
# compilation of executables
message(STATUS "configuring executables...")
add_executable(mainTest ${SOURCES_PATH}/mainTest.cpp) # Use simple name as a target
# compilation of libraries
message(STATUS "configuring libraries...")
add_library(background_substractor ${SOURCES_PATH}/background_substractor.cpp) # Use simple name as a target
# set linker options
# Command below is no-op: OpenCV libraries enumerated using absolute paths
# link_directories(${OpenCV_LINK_DIRECTORIES})
target_link_libraries(mainTest ${OpenCV_LIBS}) # Variable OpenCV_LIBS contains OpenCV libraries needed to link with
target_link_libraries(background_substractor ${OpenCV_LIBS})
message(STATUS "cmake configuration complete")