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Cross compile OpenCV to a RaspberryPI

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  • 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
                                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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