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Cross compile OpenCV to a RaspberryPI

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  • jsulmJ jsulm

    @hamzaelazizi Depends on how you created it. There are different ways. For example you can simply connect the SD card from your RaspberryPi to your development machine. Or you can copy the /usr content (at least lib and include subfolders) to your development machine.

    hamzaelaziziH Offline
    hamzaelaziziH Offline
    hamzaelazizi
    wrote on last edited by
    #6

    @jsulm do i need to install OpenCV On the host machine as well ?

    jsulmJ 1 Reply Last reply
    0
    • hamzaelaziziH hamzaelazizi

      @jsulm do i need to install OpenCV On the host machine as well ?

      jsulmJ Offline
      jsulmJ Offline
      jsulm
      Lifetime Qt Champion
      wrote on last edited by
      #7

      @hamzaelazizi No, why should you if you want to cross compile? Host libraries have nothing to do with RaspberryPi.

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

      hamzaelaziziH 1 Reply Last reply
      0
      • jsulmJ jsulm

        @hamzaelazizi No, why should you if you want to cross compile? Host libraries have nothing to do with RaspberryPi.

        hamzaelaziziH Offline
        hamzaelaziziH Offline
        hamzaelazizi
        wrote on last edited by
        #8

        @jsulm then what path should i include in my .pro file ? i've created a small qt program on my host machine and i simply want to open an image and display it on the raspberry but i don't know what to include in my .pro file and when i compile it i get the error saying " :-1: error: cannot find -lm "

        jsulmJ 1 Reply Last reply
        0
        • hamzaelaziziH hamzaelazizi

          @jsulm then what path should i include in my .pro file ? i've created a small qt program on my host machine and i simply want to open an image and display it on the raspberry but i don't know what to include in my .pro file and when i compile it i get the error saying " :-1: error: cannot find -lm "

          jsulmJ Offline
          jsulmJ Offline
          jsulm
          Lifetime Qt Champion
          wrote on last edited by
          #9

          @hamzaelazizi said in Cross compile OpenCV to a RaspberryPI:

          then what path should i include in my .pro file ?

          The libraries you need I guess? Or what exactly are you asking?
          In this case OpenCV libs you're using.
          In QtCreator you should have a Kit for cross compilation where you set your cross compiled Qt and also path to your sysroot.
          You need to understand the difference between compiling for host and cross compalation. If you compile for the host then libraries/headers installed on your host are used. But if you're doing cross compilation libraries and headers are taken from the sysroot.
          You can find here information about QtCreator set-up for cross compilation: https://www.ics.com/blog/configuring-qt-creator-raspberry-pi

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

          hamzaelaziziH 1 Reply Last reply
          0
          • jsulmJ jsulm

            @hamzaelazizi said in Cross compile OpenCV to a RaspberryPI:

            then what path should i include in my .pro file ?

            The libraries you need I guess? Or what exactly are you asking?
            In this case OpenCV libs you're using.
            In QtCreator you should have a Kit for cross compilation where you set your cross compiled Qt and also path to your sysroot.
            You need to understand the difference between compiling for host and cross compalation. If you compile for the host then libraries/headers installed on your host are used. But if you're doing cross compilation libraries and headers are taken from the sysroot.
            You can find here information about QtCreator set-up for cross compilation: https://www.ics.com/blog/configuring-qt-creator-raspberry-pi

            hamzaelaziziH Offline
            hamzaelaziziH Offline
            hamzaelazizi
            wrote on last edited by
            #10

            @jsulm i copied my folders "lib" and "include" where most of my OpenCV libraries are from the raspberry to the sysroot folder on my host machine but when i try to compile it keeps saying ":-1: error: cannot find -lm" i don't know why ?? i know it's an issue related to the math library but i don't know why it says this

            jsulmJ 1 Reply Last reply
            0
            • hamzaelaziziH hamzaelazizi

              @jsulm i copied my folders "lib" and "include" where most of my OpenCV libraries are from the raspberry to the sysroot folder on my host machine but when i try to compile it keeps saying ":-1: error: cannot find -lm" i don't know why ?? i know it's an issue related to the math library but i don't know why it says this

              jsulmJ Offline
              jsulmJ Offline
              jsulm
              Lifetime Qt Champion
              wrote on last edited by
              #11

              @hamzaelazizi How do you build?
              Do you build in QtCreator?
              How does your sysroot look like? Its structure should be: PATH_TO_SYSROOT/usr/* (* is lib and include)

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

              hamzaelaziziH 1 Reply Last reply
              0
              • jsulmJ jsulm

                @hamzaelazizi How do you build?
                Do you build in QtCreator?
                How does your sysroot look like? Its structure should be: PATH_TO_SYSROOT/usr/* (* is lib and include)

                hamzaelaziziH Offline
                hamzaelaziziH Offline
                hamzaelazizi
                wrote on last edited by
                #12

                @jsulm yes i build in Qt Creator
                i didn't understand your second question but here is my sysroot path : "/home/rpi-qt/sysroot/* (* is lib and include and local)
                local is the file i copied with the OpenCV libraries in
                when i build and compile another project, it works and i can deploy the application on the Raspberry but when i try to do something with OpenCV it shows that error "cannot find -lm"

                JonBJ 1 Reply Last reply
                0
                • hamzaelaziziH hamzaelazizi

                  @jsulm yes i build in Qt Creator
                  i didn't understand your second question but here is my sysroot path : "/home/rpi-qt/sysroot/* (* is lib and include and local)
                  local is the file i copied with the OpenCV libraries in
                  when i build and compile another project, it works and i can deploy the application on the Raspberry but when i try to do something with OpenCV it shows that error "cannot find -lm"

                  JonBJ Offline
                  JonBJ Offline
                  JonB
                  wrote on last edited by JonB
                  #13

                  @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 1 Reply Last reply
                  0
                  • 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
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