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Cross compile OpenCV to a RaspberryPI

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  • JonBJ JonB

    @hamzaelazizi said in Cross compile OpenCV to a RaspberryPI:

    error "cannot find -lm"

    It is looking for file libm.a. Probably because OpenCV needs the math library. On Ubuntu, for example, that is in /usr/lib/x86_64-linux-gnu/libm.a. I don't know where yours is/is supposed to be, in your cross-compilation situation. Linux command find / -name libm.a -print 2>/dev/null on whichever machine, and wherever you need to look down from where mine specifies /, should find it if present.

    hamzaelaziziH Offline
    hamzaelaziziH Offline
    hamzaelazizi
    wrote on last edited by
    #14

    @JonB in case i was able to find its location, how can i tell Qt Creator to look for that library in that path ?

    JonBJ 1 Reply Last reply
    0
    • hamzaelaziziH hamzaelazizi

      @JonB in case i was able to find its location, how can i tell Qt Creator to look for that library in that path ?

      JonBJ Offline
      JonBJ Offline
      JonB
      wrote on last edited by
      #15

      @hamzaelazizi
      I have updated my post to give you a Linux find command to help you locate it.
      Let's see where, if anywhere, it tells you it finds it before we know how to proceed.
      I don't do cross-compilation so I don't know where you need to look or what to do about it when you find it, you may need @jsulm's help when you have told us where it is....

      hamzaelaziziH 2 Replies Last reply
      0
      • JonBJ JonB

        @hamzaelazizi
        I have updated my post to give you a Linux find command to help you locate it.
        Let's see where, if anywhere, it tells you it finds it before we know how to proceed.
        I don't do cross-compilation so I don't know where you need to look or what to do about it when you find it, you may need @jsulm's help when you have told us where it is....

        hamzaelaziziH Offline
        hamzaelaziziH Offline
        hamzaelazizi
        wrote on last edited by
        #16

        @JonB it gave me all these locations:

        /home/rnsaoberon/rpi-qt/tools/cross-pi-gcc-8.3.0-2/arm-linux-gnueabihf/libc/usr/lib/libm.a
        /home/rnsaoberon/rpi-qt/sysroot/lib/arm-linux-gnueabihf/libm.a
        /home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf/libm.a
        /usr/arm-linux-gnueabi/libhf/libm.a
        /usr/lib/x86_64-linux-gnu/libm.a
        /usr/arm-linux-gnueabihf/lib/libm.a

        i used the one with the Bold writing

        1 Reply Last reply
        0
        • JonBJ JonB

          @hamzaelazizi
          I have updated my post to give you a Linux find command to help you locate it.
          Let's see where, if anywhere, it tells you it finds it before we know how to proceed.
          I don't do cross-compilation so I don't know where you need to look or what to do about it when you find it, you may need @jsulm's help when you have told us where it is....

          hamzaelaziziH Offline
          hamzaelaziziH Offline
          hamzaelazizi
          wrote on last edited by
          #17

          @JonB after i included the one i told you about i started having other errors :

          undefined reference to cv::imshow
          undefined reference to cv::imread undefined reference to cv::wait
          undefined reference to `cv::Mat

          JonBJ 1 Reply Last reply
          0
          • hamzaelaziziH hamzaelazizi

            @JonB after i included the one i told you about i started having other errors :

            undefined reference to cv::imshow
            undefined reference to cv::imread undefined reference to cv::wait
            undefined reference to `cv::Mat

            JonBJ Offline
            JonBJ Offline
            JonB
            wrote on last edited by
            #18

            @hamzaelazizi
            As I said, since I know nothing about cross-compilation or RPi you will have to await a comment from e.g. @jsulm as to what you are supposed to do....

            hamzaelaziziH 1 Reply Last reply
            0
            • JonBJ JonB

              @hamzaelazizi
              As I said, since I know nothing about cross-compilation or RPi you will have to await a comment from e.g. @jsulm as to what you are supposed to do....

              hamzaelaziziH Offline
              hamzaelaziziH Offline
              hamzaelazizi
              wrote on last edited by
              #19

              @JonB Okey i'll be waiting for him to reply back, hopefully he does

              jsulmJ 1 Reply Last reply
              0
              • hamzaelaziziH hamzaelazizi

                @JonB Okey i'll be waiting for him to reply back, hopefully he does

                jsulmJ Offline
                jsulmJ Offline
                jsulm
                Lifetime Qt Champion
                wrote on last edited by
                #20

                @hamzaelazizi Try this (add it to your pro file):

                LIBS += -L/usr/lib/arm-linux-gnueabihf -lm
                

                https://forum.qt.io/topic/113070/qt-code-of-conduct

                hamzaelaziziH 1 Reply Last reply
                2
                • jsulmJ jsulm

                  @hamzaelazizi Try this (add it to your pro file):

                  LIBS += -L/usr/lib/arm-linux-gnueabihf -lm
                  
                  hamzaelaziziH Offline
                  hamzaelaziziH Offline
                  hamzaelazizi
                  wrote on last edited by
                  #21

                  @jsulm yes i changed the path to the one i have and it worked but it then started showing these different errors :

                  undefined reference to cv::imshow
                  undefined reference to cv::imread
                  undefined reference to cv::wait
                  undefined reference to cv::Mat

                  1 Reply Last reply
                  0
                  • hamzaelaziziH Offline
                    hamzaelaziziH Offline
                    hamzaelazizi
                    wrote on last edited by
                    #22

                    here's my .pro file code :

                    TEMPLATE = app
                    CONFIG += console c++11
                    CONFIG -= app_bundle
                    CONFIG -= qt
                    
                    INCLUDEPATH += /home/rnsaoberon/rpi-qt/sysroot/usr/local/include/opencv4
                    #DEPENDPATH += /home/rnsaoberon/rpi-qt/sysroot/usr/local/include/opencv4
                    
                    QT_CONFIG -= no-pkg-config
                    
                    LIBS += `pkg-config --cflags --libs opencv4`
                    
                    LIBS += -L/home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf -lm
                    #CONFIG += link_pkgconfig
                    #PKGCONFIG += opencv4
                    
                    SOURCES += \
                            main.cpp
                    
                    # Default rules for deployment.
                    qnx: target.path = /tmp/$${TARGET}/bin
                    else: unix:!android: target.path = /home/pi/$${TARGET}
                    !isEmpty(target.path): INSTALLS += target
                    

                    and here's my main c++ code :

                    #include <opencv2/highgui.hpp>
                    
                    int main()
                    {
                        cv::Mat img = cv::imread("/home/pi/Pictures/drake.jpg");
                        cv::imshow("Window",img);
                        cv::waitKey(0);
                    
                        return 0;
                    }
                    
                    JonBJ jsulmJ 2 Replies Last reply
                    0
                    • hamzaelaziziH hamzaelazizi

                      here's my .pro file code :

                      TEMPLATE = app
                      CONFIG += console c++11
                      CONFIG -= app_bundle
                      CONFIG -= qt
                      
                      INCLUDEPATH += /home/rnsaoberon/rpi-qt/sysroot/usr/local/include/opencv4
                      #DEPENDPATH += /home/rnsaoberon/rpi-qt/sysroot/usr/local/include/opencv4
                      
                      QT_CONFIG -= no-pkg-config
                      
                      LIBS += `pkg-config --cflags --libs opencv4`
                      
                      LIBS += -L/home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf -lm
                      #CONFIG += link_pkgconfig
                      #PKGCONFIG += opencv4
                      
                      SOURCES += \
                              main.cpp
                      
                      # Default rules for deployment.
                      qnx: target.path = /tmp/$${TARGET}/bin
                      else: unix:!android: target.path = /home/pi/$${TARGET}
                      !isEmpty(target.path): INSTALLS += target
                      

                      and here's my main c++ code :

                      #include <opencv2/highgui.hpp>
                      
                      int main()
                      {
                          cv::Mat img = cv::imread("/home/pi/Pictures/drake.jpg");
                          cv::imshow("Window",img);
                          cv::waitKey(0);
                      
                          return 0;
                      }
                      
                      JonBJ Offline
                      JonBJ Offline
                      JonB
                      wrote on last edited by JonB
                      #23

                      @hamzaelazizi said in Cross compile OpenCV to a RaspberryPI:

                      LIBS += -L/home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf -lm

                      While you await @jsulm who actually knows something about this...!

                      I believe you are saying:

                      • without -L/home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf, although it cannot find the -lm library, you do not get errors undefined reference to cv::..., right?
                      • with -L/home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf, it finds the math library, but you do get errors undefined reference to cv::..., right?

                      In that case, by putting /home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf high on the library directory search list the cv::... stuff it also needs is no longer found, because it must find some different cv library archives (in that specified directory) instead of what it used to find, and those libraries do not include something which would resolve those references.

                      What you do/are supposed to do with that I do not know.....

                      UPDATE
                      Oh, maybe not. Those "undefined"s may always have been there. But when it cannot resolve the -lm on the link line it will stop there and won't get as far as the final step of linkage where it would notice undefineds. So the -L/home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf may be nothing to do with the "undefined"s....

                      You might start by running pkg-config --cflags --libs opencv4 in a terminal, to at least see what that is producing. E.g. if that is not even outputting any library paths to put into your LIBS it's not right....

                      hamzaelaziziH 1 Reply Last reply
                      1
                      • hamzaelaziziH hamzaelazizi

                        here's my .pro file code :

                        TEMPLATE = app
                        CONFIG += console c++11
                        CONFIG -= app_bundle
                        CONFIG -= qt
                        
                        INCLUDEPATH += /home/rnsaoberon/rpi-qt/sysroot/usr/local/include/opencv4
                        #DEPENDPATH += /home/rnsaoberon/rpi-qt/sysroot/usr/local/include/opencv4
                        
                        QT_CONFIG -= no-pkg-config
                        
                        LIBS += `pkg-config --cflags --libs opencv4`
                        
                        LIBS += -L/home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf -lm
                        #CONFIG += link_pkgconfig
                        #PKGCONFIG += opencv4
                        
                        SOURCES += \
                                main.cpp
                        
                        # Default rules for deployment.
                        qnx: target.path = /tmp/$${TARGET}/bin
                        else: unix:!android: target.path = /home/pi/$${TARGET}
                        !isEmpty(target.path): INSTALLS += target
                        

                        and here's my main c++ code :

                        #include <opencv2/highgui.hpp>
                        
                        int main()
                        {
                            cv::Mat img = cv::imread("/home/pi/Pictures/drake.jpg");
                            cv::imshow("Window",img);
                            cv::waitKey(0);
                        
                            return 0;
                        }
                        
                        jsulmJ Offline
                        jsulmJ Offline
                        jsulm
                        Lifetime Qt Champion
                        wrote on last edited by
                        #24

                        @hamzaelazizi said in Cross compile OpenCV to a RaspberryPI:

                        INCLUDEPATH += /home/rnsaoberon/rpi-qt/sysroot/usr/local/include/opencv4

                        Please change all these paths!
                        You do NOT have to put the path of your sysroot!
                        It should look like this:

                        INCLUDEPATH += /usr/local/include/opencv4
                        

                        Also, why /usr/local?! I doubt OpenCV packages from your OS install anything in /usr/local! Please fix this!

                        "LIBS += -L/home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf -lm" - this is also not what I suggested! Why do you add sysroot path everywhere?

                        LIBS += -L/usr/lib/arm-linux-gnueabihf -lm
                        

                        The errors you posted mean that OpenCV libs are not found. If you really install OpenCV using your OS packet manager on your RaspberryPi the libs should be somewhere in /usr/lib and it should be enough to add -lLIBNAME to pro file.

                        https://forum.qt.io/topic/113070/qt-code-of-conduct

                        1 Reply Last reply
                        3
                        • JonBJ JonB

                          @hamzaelazizi said in Cross compile OpenCV to a RaspberryPI:

                          LIBS += -L/home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf -lm

                          While you await @jsulm who actually knows something about this...!

                          I believe you are saying:

                          • without -L/home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf, although it cannot find the -lm library, you do not get errors undefined reference to cv::..., right?
                          • with -L/home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf, it finds the math library, but you do get errors undefined reference to cv::..., right?

                          In that case, by putting /home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf high on the library directory search list the cv::... stuff it also needs is no longer found, because it must find some different cv library archives (in that specified directory) instead of what it used to find, and those libraries do not include something which would resolve those references.

                          What you do/are supposed to do with that I do not know.....

                          UPDATE
                          Oh, maybe not. Those "undefined"s may always have been there. But when it cannot resolve the -lm on the link line it will stop there and won't get as far as the final step of linkage where it would notice undefineds. So the -L/home/rnsaoberon/rpi-qt/sysroot/usr/lib/arm-linux-gnueabihf may be nothing to do with the "undefined"s....

                          You might start by running pkg-config --cflags --libs opencv4 in a terminal, to at least see what that is producing. E.g. if that is not even outputting any library paths to put into your LIBS it's not right....

                          hamzaelaziziH Offline
                          hamzaelaziziH Offline
                          hamzaelazizi
                          wrote on last edited by
                          #25

                          @JonB i think i have got it to work, and i'm still in shock...

                          i added this code in .pro file : LIBS += -L/home/rnsaoberon/rpi-qt/sysroot/usr/local/lib -lopencv_core -lopencv_imgproc -lopencv_highgui -lopencv_imgcodecs

                          Apparently, Qt Creator wasn't able to find the libraries necessary for the application, so when i asked it to add them, it worked !
                          Tho, i'm sure i'll encounter more problems in the near futur, but that's enouh errors for one day.
                          i still have one question which is irrelevant to this topic : How can i use Qt to work with a thermal camera that uses SPI(GPIO) protocol to communicate. a FLIR Lepton thermal camera to be specific, Thank you !

                          jsulmJ 1 Reply Last reply
                          0
                          • hamzaelaziziH hamzaelazizi

                            @JonB i think i have got it to work, and i'm still in shock...

                            i added this code in .pro file : LIBS += -L/home/rnsaoberon/rpi-qt/sysroot/usr/local/lib -lopencv_core -lopencv_imgproc -lopencv_highgui -lopencv_imgcodecs

                            Apparently, Qt Creator wasn't able to find the libraries necessary for the application, so when i asked it to add them, it worked !
                            Tho, i'm sure i'll encounter more problems in the near futur, but that's enouh errors for one day.
                            i still have one question which is irrelevant to this topic : How can i use Qt to work with a thermal camera that uses SPI(GPIO) protocol to communicate. a FLIR Lepton thermal camera to be specific, Thank you !

                            jsulmJ Offline
                            jsulmJ Offline
                            jsulm
                            Lifetime Qt Champion
                            wrote on last edited by
                            #26

                            @hamzaelazizi said in Cross compile OpenCV to a RaspberryPI:

                            Apparently, Qt Creator wasn't able to find the libraries necessary for the application

                            Well, you have to tell the build system (not QtCreator) which libs your app needs, there is no magic.
                            Please also consider my previous post.

                            https://forum.qt.io/topic/113070/qt-code-of-conduct

                            hamzaelaziziH 1 Reply Last reply
                            3
                            • jsulmJ jsulm

                              @hamzaelazizi said in Cross compile OpenCV to a RaspberryPI:

                              Apparently, Qt Creator wasn't able to find the libraries necessary for the application

                              Well, you have to tell the build system (not QtCreator) which libs your app needs, there is no magic.
                              Please also consider my previous post.

                              hamzaelaziziH Offline
                              hamzaelaziziH Offline
                              hamzaelazizi
                              wrote on last edited by
                              #27

                              @jsulm Thank you for your time and effort, sir ! much appreciated

                              1 Reply Last reply
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