QT Creator links different library than command line - opencv

Question

I have a problem I am unable to understand.
I am trying to code a project using openCV 3.1. I want to code inside the QT Creator Environment, because I'm used to that. I do not necessarily need any QT specific features at the moment, I'm working with Ubuntu 14.04.
The problem is, that whenever I try to build inside the QT Creator, it does not build with the following error, but it works if I build from the command line.
10:57:36: Starting: "/usr/bin/cmake" --build . --target all
Linking CXX executable arucoTest
CMakeFiles/arucoTest.dir/PoseEstimator.cpp.o: In function `PoseEstimator::generateMarkers(std::string, int)':
PoseEstimator.cpp:(.text+0x56): undefined reference to `cv::aruco::getPredefinedDictionary(cv::aruco::PREDEFINED_DICTIONARY_NAME)'
PoseEstimator.cpp:(.text+0xb7): undefined reference to `cv::aruco::drawMarker(cv::Ptr<cv::aruco::Dictionary>&, int, int, cv::_OutputArray const&, int)'
PoseEstimator.cpp:(.text+0x1a9): undefined reference to `cv::imwrite(cv::String const&, cv::_InputArray const&, std::vector<int, std::allocator<int> > const&)'
CMakeFiles/arucoTest.dir/PoseEstimator.cpp.o: In function `cv::String::~String()':
PoseEstimator.cpp:(.text._ZN2cv6StringD2Ev[_ZN2cv6StringD5Ev]+0x14): undefined reference to `cv::String::deallocate()'
CMakeFiles/arucoTest.dir/PoseEstimator.cpp.o: In function `cv::String::String(std::string const&)':
PoseEstimator.cpp:(.text._ZN2cv6StringC2ERKSs[_ZN2cv6StringC5ERKSs]+0x69): undefined reference to `cv::String::allocate(unsigned long)'
collect2: error: ld returned 1 exit status
make[2]: *** [arucoTest] Error 1
make[1]: *** [CMakeFiles/arucoTest.dir/all] Error 2
make: *** [all] Error 2
10:57:36: The process "/usr/bin/cmake" exited with code 2.
So it is some kind of linker error. When I inspect my cmake file and output, I see this:
Running "/usr/bin/cmake /XYZ/arucoTest '-GCodeBlocks - Unix Makefiles'" in /XYZ/arucoTest/testbuild.
-- OpenCV library status:
-- version: 2.4.8
-- libraries: opencv_videostab;opencv_video;opencv_ts;opencv_superres;opencv_stitching;opencv_photo;opencv_ocl;opencv_objdetect;opencv_ml;opencv_legacy;opencv_imgproc;opencv_highgui;opencv_gpu;opencv_flann;opencv_features2d;opencv_core;opencv_contrib;opencv_calib3d
-- include path: /usr/include/opencv;/usr/include
-- Configuring done
-- Generating done
-- Build files have been written to: /XYZ/arucoTest/testbuild
As you can see, it only finds openCV 2.4.8, which I still need because of old ROS Indigo projects. However, if I execute the exact same cmake file and build from the commandline, it works perfectly:
username#pc:/XYZ/arucoTest/build$ cmake ..
-- The C compiler identification is GNU 4.8.4
-- The CXX compiler identification is GNU 4.8.4
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- OpenCV library status:
-- version: 3.1.0
-- libraries: opencv_xphoto;opencv_xobjdetect;opencv_ximgproc;opencv_xfeatures2d;opencv_tracking;opencv_text;opencv_surface_matching;opencv_structured_light;opencv_stereo;opencv_saliency;opencv_rgbd;opencv_reg;opencv_plot;opencv_optflow;opencv_line_descriptor;opencv_fuzzy;opencv_face;opencv_dpm;opencv_dnn;opencv_datasets;opencv_ccalib;opencv_bioinspired;opencv_bgsegm;opencv_aruco;opencv_viz;opencv_videostab;opencv_videoio;opencv_video;opencv_superres;opencv_stitching;opencv_shape;opencv_photo;opencv_objdetect;opencv_ml;opencv_imgproc;opencv_imgcodecs;opencv_highgui;opencv_flann;opencv_features2d;opencv_core;opencv_calib3d
-- include path: /usr/local/include/opencv;/usr/local/include
-- Configuring done
-- Generating done
-- Build files have been written to: /XYZ/arucoTest/build
veith#roethlinLT:/XYZ/arucoTest/build$ make
Scanning dependencies of target arucoTest
[100%] Building CXX object CMakeFiles/arucoTest.dir/PoseEstimator.cpp.o
Linking CXX executable arucoTest
[100%] Built target arucoTest
As you can see I'm building in 2 different folders, because I found that if I cmake in the same folder, it does not work, even if I remove everything in that folder and cmake again from the command line. Also notice, that it finds 2 different include paths depending on where I start the cmake from.
My makefile looks like this (not very crazy), I'm using this exact same file for both cases.
project(arucoTest)
cmake_minimum_required(VERSION 2.8)
find_package(OpenCV REQUIRED)
message(STATUS "OpenCV library status:")
message(STATUS " version: ${OpenCV_VERSION}")
message(STATUS " libraries: ${OpenCV_LIBS}")
message(STATUS " include path: ${OpenCV_INCLUDE_DIRS}")
set(HEADER_LIST PoseEstimator.h)
set(SRC_LIST PoseEstimator.cpp)
add_executable(${PROJECT_NAME} ${SRC_LIST})
target_link_libraries(${PROJECT_NAME} ${OpenCV_LIBS})
Using ccmake and the QT build in inspection window, I see that the OpenCV_DIR variable is set to 2 different things: On command line:
OpenCV_DIR /usr/local/share/OpenCV
In QT Creator:
OpenCV_DIR /ust/share/OpenCV
How do I set this to automatically select the right folder inside QT Creator as well? I really have no idea what could cause this!
Thanks!

Answer 1

Cache variable OpenCV_DIR is set by searching with command find_package (in config mode). While search mechanism is fully deterministic (it is described in the doc), it uses some envorinment variables which may differ under your shell and in QT Creator.
Just a guess, QT Creator may set CMAKE_PREFIX_PATH environment variable to contain /usr directory, so it finds an installation under /usr before one under /usr/local.
For choose specific OpenCV installation, just set OpenCV_DIR cache variable accordingly and rerun configuration process.