I am trying to run an OpenCV program written in C++ on Ubuntu. I followed this tutorial to install OpenCV on my system.
I then followed this tutorial to run my code with the following Cmake commands as specified in the tutorial:
cmake_minimum_required(VERSION 2.8)
project( PedestrianDetection )
find_package( OpenCV REQUIRED )
add_executable( PedestrianDetection PedestrianDetection.cpp )
target_link_libraries( ${OpenCV_LIBS} )
However, Cmake gives me the following output:
CMake Error at CMakeLists.txt:5 (target_link_libraries):
Cannot specify link libraries for target "opencv_videostab" which is not
built by this project.
Can someone point me in the right direction to link the libraries?
By the way, I am using OpenCV2.4.8
from the documentation
target_link_libraries: Link a target to given libraries.
target_link_libraries(<target> [item1 [item2 [...]]]
[[debug|optimized|general] <item>] ...)
Specify libraries or flags to use when linking a given target. The
named must have been created in the current directory by a
command such as add_executable or add_library. The remaining arguments
specify library names or flags.
try instead
target_link_libraries(PedestrianDetection ${OpenCV_LIBS})
Related
I am developing a C++ library, including OpenCV, which will be used in a cross-platform Xamarin solution through a wrapper and the NuGet packaging system (see this guide). I configured a CMakeLists.txt file but I simply cannot get OpenCV to be correctly linked for both static (iOS) and dynamic (Android) libraries.
I tried to change the OpenCV_DIR variable, install and build OpenCV from sources and manually include the content of the OpenCV_INCLUDE_DIRS variable but nothing worked. I also noticed that the linking works when only using cv::Point. But the linking does not work when using cv::Mat, which I do not understand the reason.
The following is the CMakeLists.txt that I am using :
cmake_minimum_required (VERSION 3.2)
project (MyLib C CXX)
enable_testing()
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
MESSAGE(STATUS "CMAKE_CXX_FLAGS: " ${CMAKE_CXX_FLAGS})
# Source and headers files
set(SOURCES File1.cpp File2.cpp)
set(HEADERS File1.h File2.h)
# Library
if(BUILD_SHARED_LIBS)
add_library (MyLib SHARED ${SOURCES} ${HEADERS})
target_compile_definitions(MyLib PUBLIC IS_BUILDING_SHARED)
else()
add_library (MyLib STATIC ${SOURCES} ${HEADERS})
endif()
# Dependencies
set(OpenCV_DIR /usr/local/Cellar/opencv/4.5.0_1/lib/cmake/opencv4)
find_package(OpenCV REQUIRED)
message(STATUS "OpenCV_INCLUDE_DIRS = ${OpenCV_INCLUDE_DIRS}")
message(STATUS "OpenCV_LIBS = ${OpenCV_LIBS}")
message(STATUS "OpenCV_DIR = ${OpenCV_DIR}")
include_directories(${OpenCV_INCLUDE_DIRS})
target_link_libraries(MyLib ${OpenCV_LIBS})
The following shows the location of OpenCV's files that are used during the build process. Everything seems alright.
-- OpenCV_INCLUDE_DIRS = /usr/local/Cellar/opencv/4.5.0_1/include/opencv4
-- OpenCV_LIBS = opencv_calib3d;opencv_core;opencv_dnn;opencv_features2d;opencv_flann;opencv_gapi;opencv_highgui;opencv_imgcodecs;opencv_imgproc;opencv_ml;opencv_objdetect;opencv_photo;opencv_stitching;opencv_video;opencv_videoio;opencv_alphamat;opencv_aruco;opencv_bgsegm;opencv_bioinspired;opencv_ccalib;opencv_datasets;opencv_dnn_objdetect;opencv_dnn_superres;opencv_dpm;opencv_face;opencv_freetype;opencv_fuzzy;opencv_hfs;opencv_img_hash;opencv_intensity_transform;opencv_line_descriptor;opencv_mcc;opencv_optflow;opencv_phase_unwrapping;opencv_plot;opencv_quality;opencv_rapid;opencv_reg;opencv_rgbd;opencv_saliency;opencv_sfm;opencv_shape;opencv_stereo;opencv_structured_light;opencv_superres;opencv_surface_matching;opencv_text;opencv_tracking;opencv_videostab;opencv_viz;opencv_xfeatures2d;opencv_ximgproc;opencv_xobjdetect;opencv_xphoto
-- OpenCV_DIR = /usr/local/Cellar/opencv/4.5.0_1/lib/cmake/opencv4
Android
The following is the commands that I am using to build the Android dynamic library (.so). I have installed the NDK and am building for each ABI (x86, x86_64, armeabi-v7a, arm64-v8a).
cmake ../.. -DCMAKE_TOOLCHAIN_FILE=/Users/$USER/Library/Android/sdk/ndk-bundle/build/cmake/android.toolchain.cmake -DANDROID_NATIVE_API_LEVEL=21 -DANDROID_ABI=$abi_name -DBUILD_SHARED_LIBS=ON
cmake --build . --config Release
I directly get an error when building the library which is the following.
ld: error: /usr/local/Cellar/opencv/4.5.0_1/lib/libopencv_gapi.4.5.0.dylib: unknown file type
ld: error: /usr/local/Cellar/opencv/4.5.0_1/lib/libopencv_stitching.4.5.0.dylib: unknown file type
[...]
ld: error: /usr/local/Cellar/opencv/4.5.0_1/lib/libopencv_rapid.4.5.0.dylib: unknown file type
ld: error: too many errors emitted, stopping now (use -error-limit=0 to see all errors)
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
iOS
The following is the commands that I am using to build the iOS static library (.a). I am using leetal's ​cmake toolchain file from this repository.
cmake ../.. -G Xcode -DCMAKE_TOOLCHAIN_FILE=../../ios.toolchain.cmake -DPLATFORM=OS64COMBINED -DBUILD_SHARED_LIBS=OFF
cmake --build . --config Release
The compilation of the static library seems to work because no error message is printed. However, when the library is used in the final Xamarin solution, the linked library cannot be found and the following error is shown.
Native linking failed, undefined symbol: cv::Mat::deallocate(). Please verify that all the necessary frameworks have been referenced and native libraries are properly linked in. (MT5210)
Question
What am I missing in order to properly compile and link OpenCV into my C++ library ?
I am working on macOS Big Sur and uses the following tools versions:
cmake : 3.20.0-rc5
ndk : 23.0.7196353
apple clang : 12.0.0
I hope that the description of my problem is clear enough and I thank you in advance for any help.
We had same problems, including Xamarin's DllNotFoundException with message from last comment, which led me to this topic. What fixed the exception for us in the end was linking statically to OpenCV *.a libs instead of linking to the shared libopencv_java4.so file. So we now have a huge 30MB nativelib.so file for each android ABI in build output, instead of a pair of small nativelib.so and libopencv_java4.so per ABI. CMakeLists looks like this:
set( OpenCV_DIR "~/opencv/build/OpenCV-android-sdk/sdk/native/jni" )
find_package( OpenCV REQUIRED )
target_link_libraries( # Specifies the target library.
nativelib
${OpenCV_LIBS})
Another thing in our project is we use OpenCV optional modules and had to create a custom OpenCV build, which I guess ensures our native library and OpenCV are compiled against same NDK version. I suppose using the prebuilt OpenCV distribution and compiling against a different NDK version could lead to problems too otherwise.
When using some libraries like OpenCV with C/C++, variables like OpenCV_LIBS are used to point the compiler/linker to the relevant directories.
Examples using cmake:
include_directories( ${OpenCV_INCLUDE_DIRS} )
target_link_libraries( project_name ${OpenCV_LIBS} )
How can I check where such variables point at? I've tried typing set or printenv in terminal but it shows only some system variables. Also how can I set/change such variables?
Those variables are determined by cmake (see OpenCVConfig.cmake for a more detailed description of opencv CMake variables available).
To see those values you can add message() calls after the find_package(OpenCV) call to your project's CMakeLists.txt:
find_package(OpenCV)
message(STATUS "OpenCV_INCLUDE_DIRS = ${OpenCV_INCLUDE_DIRS}")
message(STATUS "OpenCV_LIBS = ${OpenCV_LIBS}")
Alternatively you can run find_package via a CMake command line option.
Here are a few examples (the CMAKE_PREFIX_PATH part is optional if CMake is not able to find your libraries installation path automatically):
MODE=COMPILE giving include directories (e.g. with MSVC compiler)
$ cmake
--find-package
-DNAME=OpenCV
-DCOMPILER_ID=MSVC -DMSVC_VERSION=1700
-DLANGUAGE=CXX
-DMODE=COMPILE
-DCMAKE_PREFIX_PATH:PATH=/path/to/your/OpenCV/build
MODE=LINK giving link libraries (e.g. with GNU compiler)
$ cmake
--find-package
-DNAME=OpenCV
-DCOMPILER_ID=GNU
-DLANGUAGE=CXX
-DMODE=LINK
-DCMAKE_PREFIX_PATH:PATH=/path/to/your/OpenCV/build
Note: This CMake call will create a CMakeFiles sub-directory in your current working directory.
References
Using OpenCV with gcc and CMake
CMakeFindPackageMode CMake module documentation
I have installed opencv2.4.9(With No CUDA) by unzip opencv2.4.9.zip in home.
Many successful codes are using this library.
Now I wanna rebuild opencv2.4.9(with CUDA) in another folder.
I don't wanna delete the previous folder because I don't wanna face any problem later on and make my older code can't function.
So, the question is how to change the name of the directory? Seems like we link the package with library in CMake like below:
include_directories( ${catkin_INCLUDE_DIRS} ${OpenCV_INCLUDE_DIRS} )
find_package( OpenCV REQUIRED )
find_package(catkin REQUIRED COMPONENTS cv_bridge image_transport
OpenCV roscpp rospy std_msgs )
the name of directory is just OpenCV.
So if I got more than one OpenCV library in home, how could I link them separately?
And how to make c++ link to the library if we could change the name?
add_executable(xxx src/xxx.cpp)
target_link_libraries(xxx ${catkin_LIBRARIES} ${OpenCV_LIBRARIES})
Libraries can be included and linked with include_directories() and link_directories(), like this:
cmake_minimum_required(VERSION 2.4.6)
include($ENV{ROS_ROOT}/core/rosbuild/rosbuild.cmake)
...
include_directories(${PROJECT_SOURCE_DIR})
include_directories(/path/to/opencv/OpenCV-2.4.1/include)
link_directories(/path/to/opencv/OpenCV-2.4.1/lib)
...
# Set the build type. Options are:
# Coverage : w/ debug symbols, w/o op ...
So you should not forget the linking in the CMakeLists.txt and maybe remove the standard linking to your current OpenCV libs.
I use DCMTK in my application and for compilation use cmake file. cmake finds all libraries (at least headers, because in compiles source files to .o files) the only problem is that during linking it tries to find dynamic libraries for DCMTK. I compiled one as static, so I do not have .so files. As a result it gives me error :No rule to make target /usr/lib/libdcmdata.so, needed by dcm_seg. Stop.
I use Ubuntu 14.04 x64.
It confuses me pretty much. So, what's the problems?
cmake file:
cmake_minimum_required(VERSION 2.6)
project(dcm_segm)
set(CMAKE_CXX_FLAGS "-std=c++0x ${CMAKE_CXX_FLAGS} -g -ftest-coverage -fprofile-arcs")
set(Boost_USE_STATIC_LIBS ON)
set(OpenCV_USE_STATIC_LIBS ON)
set(DCMTK_USE_STATIC_LIBS ON)
set(OpenCV_STATIC ON)
find_package( VTK REQUIRED )
find_package( OpenCV REQUIRED )
find_package( Boost COMPONENTS system filesystem REQUIRED )
find_package( DCMTK REQUIRED )
include(${VTK_USE_FILE} )
link_directories(${OpenCV_LIB_DIR})
add_executable(dcm_seg main.cpp DICOMin.cpp Ensemble.cpp Ensemble3dExtension.cpp point_3d.cpp RegionGrow.cpp)
target_link_libraries(dcm_seg ${VTK_LIBRARIES} ${OpenCV_LIBS} ${DCMTK_LIBRARIES} ${Boost_LIBRARIES})
Can you check the content of ${DCMTK_LIBRARIES} (it should be a list of paths to DCMTK static libraries) ?
you can also check the following CMake entries during the CMake configuration:
DCMTK_DIR /path/to/DCMTK/install
DCMTK_config_INCLUDE_DIR /path/to/DCMTK/install/include/dcmtk/config
DCMTK_dcmdata_INCLUDE_DIR /path/to/DCMTK/install/dcmdata/include/dcmtk/dcmdata
DCMTK_dcmdata_LIBRARY_DEBUG /path/to/DCMTK/install/dcmdata/libsrc/libdcmdata.a
DCMTK_dcmdata_LIBRARY_RELEASE /path/to/DCMTK/install/dcmdata/libsrc/libdcmdata.a
[...]
Another hint: I noted in the past that find DCMTK from a build instead of an install not always works properly.
If you have trouble finding DCMTK with the script provided with CMake
(${DCMTK_LIBRARIES} doesn not content the path to you static DCMTK libs for example) you can try to use this alternative script
i wanted to run this c++/OpenCV code that i found online:
http://docs.opencv.org/doc/tutorials/features2d/feature_homography/feature_homography.html
I have a problem with CMake, it returned this error:
CMake Error at CMakeLists.txt:5 (target_link_libraries):
Cannot specify link libraries for target "SURF_Homography" which is not
built by this project.
I searched on the web the solution, and i found this
CMake OpenCV Cannot Specify Link Libraries
but i can't understand why mine don't work because it looks like the same, this is my CMakeLists file:
cmake_minimum_required(VERSION 2.8)
project( SURF_Homography )
find_package( OpenCV REQUIRED )
add_executable( SURF_Homography.cpp SURF_Homography.cpp )
target_link_libraries( SURF_Homography ${OpenCV_LIBS} )
hope you can help me
thanks
Luca
Change the add_executable line:
add_executable( SURF_Homography SURF_Homography.cpp )
Otherwise, the target you are specifying in the target_link_libraries line won't exist :)