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Cross compile OpenCV to a RaspberryPI

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  • J jsulm
    11 May 2022, 09:07

    @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)

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    hamzaelazizi
    wrote on 11 May 2022, 09:14 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"

    J 1 Reply Last reply 11 May 2022, 09:48
    0
    • H hamzaelazizi
      11 May 2022, 09:14

      @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"

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      J Online
      JonB
      wrote on 11 May 2022, 09:48 last edited by JonB 5 Nov 2022, 09:50
      #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.

      H 1 Reply Last reply 11 May 2022, 09:50
      0
      • J JonB
        11 May 2022, 09:48

        @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.

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        hamzaelazizi
        wrote on 11 May 2022, 09:50 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 ?

        J 1 Reply Last reply 11 May 2022, 09:52
        0
        • H hamzaelazizi
          11 May 2022, 09:50

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

          J Online
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          JonB
          wrote on 11 May 2022, 09:52 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....

          H 2 Replies Last reply 11 May 2022, 10:04
          0
          • J JonB
            11 May 2022, 09:52

            @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....

            H Offline
            H Offline
            hamzaelazizi
            wrote on 11 May 2022, 10:04 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
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            • J JonB
              11 May 2022, 09:52

              @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....

              H Offline
              H Offline
              hamzaelazizi
              wrote on 11 May 2022, 10:19 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

              J 1 Reply Last reply 11 May 2022, 10:20
              0
              • H hamzaelazizi
                11 May 2022, 10:19

                @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

                J Online
                J Online
                JonB
                wrote on 11 May 2022, 10:20 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....

                H 1 Reply Last reply 11 May 2022, 10:29
                0
                • J JonB
                  11 May 2022, 10:20

                  @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....

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                  hamzaelazizi
                  wrote on 11 May 2022, 10:29 last edited by
                  #19

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

                  J 1 Reply Last reply 11 May 2022, 11:02
                  0
                  • H hamzaelazizi
                    11 May 2022, 10:29

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

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                    jsulm
                    Lifetime Qt Champion
                    wrote on 11 May 2022, 11:02 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

                    H 1 Reply Last reply 11 May 2022, 11:08
                    2
                    • J jsulm
                      11 May 2022, 11:02

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

                      LIBS += -L/usr/lib/arm-linux-gnueabihf -lm
                      
                      H Offline
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                      hamzaelazizi
                      wrote on 11 May 2022, 11:08 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
                      • H Offline
                        H Offline
                        hamzaelazizi
                        wrote on 11 May 2022, 11:19 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;
                        }
                        
                        J J 2 Replies Last reply 11 May 2022, 11:35
                        0
                        • H hamzaelazizi
                          11 May 2022, 11:19

                          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;
                          }
                          
                          J Online
                          J Online
                          JonB
                          wrote on 11 May 2022, 11:35 last edited by JonB 5 Nov 2022, 11:43
                          #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....

                          H 1 Reply Last reply 11 May 2022, 11:58
                          1
                          • H hamzaelazizi
                            11 May 2022, 11:19

                            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;
                            }
                            
                            J Offline
                            J Offline
                            jsulm
                            Lifetime Qt Champion
                            wrote on 11 May 2022, 11:57 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
                            • J JonB
                              11 May 2022, 11:35

                              @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....

                              H Offline
                              H Offline
                              hamzaelazizi
                              wrote on 11 May 2022, 11:58 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 !

                              J 1 Reply Last reply 11 May 2022, 11:59
                              0
                              • H hamzaelazizi
                                11 May 2022, 11:58

                                @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 !

                                J Offline
                                J Offline
                                jsulm
                                Lifetime Qt Champion
                                wrote on 11 May 2022, 11:59 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

                                H 1 Reply Last reply 11 May 2022, 12:12
                                3
                                • J jsulm
                                  11 May 2022, 11:59

                                  @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.

                                  H Offline
                                  H Offline
                                  hamzaelazizi
                                  wrote on 11 May 2022, 12:12 last edited by
                                  #27

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

                                  1 Reply Last reply
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