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Cross compile OpenCV to a RaspberryPI

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  • J jsulm
    11 May 2022, 06:25

    @hamzaelazizi said in Cross compile OpenCV to a RaspberryPI:

    Can u please tell me how to cross compile OpenCV as well ?

    Why don't you simply install OpenCV packages (including dev packages) on your RaspberryPi (using apt) and then symply sync your sysroot?

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    hamzaelazizi
    wrote on 11 May 2022, 06:51 last edited by
    #4

    @jsulm May i ask how do i sync my sysroot exactly because i've already installed OpenCV in my RaspberryPi

    J 1 Reply Last reply 11 May 2022, 07:14
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    • H hamzaelazizi
      11 May 2022, 06:51

      @jsulm May i ask how do i sync my sysroot exactly because i've already installed OpenCV in my RaspberryPi

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      jsulm
      Lifetime Qt Champion
      wrote on 11 May 2022, 07:14 last edited by
      #5

      @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.

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

      H 1 Reply Last reply 11 May 2022, 07:18
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      • J jsulm
        11 May 2022, 07:14

        @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.

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        hamzaelazizi
        wrote on 11 May 2022, 07:18 last edited by
        #6

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

        J 1 Reply Last reply 11 May 2022, 07:19
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        • H hamzaelazizi
          11 May 2022, 07:18

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

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          J Offline
          jsulm
          Lifetime Qt Champion
          wrote on 11 May 2022, 07:19 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

          H 1 Reply Last reply 11 May 2022, 07:35
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          • J jsulm
            11 May 2022, 07:19

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

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            hamzaelazizi
            wrote on 11 May 2022, 07:35 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 "

            J 1 Reply Last reply 11 May 2022, 07:59
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            • H hamzaelazizi
              11 May 2022, 07:35

              @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 "

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              jsulm
              Lifetime Qt Champion
              wrote on 11 May 2022, 07:59 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

              H 1 Reply Last reply 11 May 2022, 08:34
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              • J jsulm
                11 May 2022, 07:59

                @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

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                hamzaelazizi
                wrote on 11 May 2022, 08:34 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

                J 1 Reply Last reply 11 May 2022, 09:07
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                • H hamzaelazizi
                  11 May 2022, 08:34

                  @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

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                  jsulm
                  Lifetime Qt Champion
                  wrote on 11 May 2022, 09:07 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

                  H 1 Reply Last reply 11 May 2022, 09:14
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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
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                    • 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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                      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
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                      • 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
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                        • 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 ?

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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
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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....

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                            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
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                              • 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 Offline
                                J Offline
                                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
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                                • 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....

                                  H Offline
                                  H Offline
                                  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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                                    J Offline
                                    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
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                                    • J jsulm
                                      11 May 2022, 11:02

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

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