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Qt 3D Camera projection matrix

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  • B Offline
    B Offline
    Bob64
    wrote on last edited by
    #1

    How is the projection matrix property of Qt 3D (Q)Camera defined? I am a complete newbie and have been trying to do some background reading as the Qt 3D docs are pretty sparse, but the only references to camera projection matrices that I have found have defined them as 3x4 matrices. This makes sense, as the mapping is from 3D homogeneous coordinates to a projection on the image plane in 2D homogeneous coordinates. However, the Qt property is a 4x4 matrix.

    Pl45m4P 1 Reply Last reply
    0
    • B Bob64

      @Pl45m4 thanks for the suggestion. A quaternion is effectively a 4D vector, so if there is any connection with the 4X4 projection matrix I suppose the columns might be quaternions. As I say, I am quite new to this stuff, but my impression is that quaternions tend to be used to represent rotations, and I am struggling to see how that might relate to a projection.

      To rephrase my original question, I guess I am looking for some description of what the matrix in Qt means geometrically, and when one might need to modify its value, etc.

      Pl45m4P Online
      Pl45m4P Online
      Pl45m4
      wrote on last edited by
      #4

      @Bob64

      Got confused by Vector4D and Matrix4x4. Sure, a quaternion is a+ib+jc+kd

      Here is probably one of the best explanations you will find out there :)
      It's Unity, but the 3D stuff is the same, but better check what your values look like.

      https://answers.unity.com/questions/1359718/what-do-the-values-in-the-matrix4x4-for-cameraproj.html


      If debugging is the process of removing software bugs, then programming must be the process of putting them in.

      ~E. W. Dijkstra

      B 1 Reply Last reply
      1
      • B Bob64

        How is the projection matrix property of Qt 3D (Q)Camera defined? I am a complete newbie and have been trying to do some background reading as the Qt 3D docs are pretty sparse, but the only references to camera projection matrices that I have found have defined them as 3x4 matrices. This makes sense, as the mapping is from 3D homogeneous coordinates to a projection on the image plane in 2D homogeneous coordinates. However, the Qt property is a 4x4 matrix.

        Pl45m4P Online
        Pl45m4P Online
        Pl45m4
        wrote on last edited by
        #2

        @Bob64

        I think it's a quaternion in its matrix form (X,Y,Z + Angle).
        https://doc.qt.io/qt-5/qquaternion.html

        https://en.wikipedia.org/wiki/Quaternion


        If debugging is the process of removing software bugs, then programming must be the process of putting them in.

        ~E. W. Dijkstra

        B 1 Reply Last reply
        0
        • Pl45m4P Pl45m4

          @Bob64

          I think it's a quaternion in its matrix form (X,Y,Z + Angle).
          https://doc.qt.io/qt-5/qquaternion.html

          https://en.wikipedia.org/wiki/Quaternion

          B Offline
          B Offline
          Bob64
          wrote on last edited by
          #3

          @Pl45m4 thanks for the suggestion. A quaternion is effectively a 4D vector, so if there is any connection with the 4X4 projection matrix I suppose the columns might be quaternions. As I say, I am quite new to this stuff, but my impression is that quaternions tend to be used to represent rotations, and I am struggling to see how that might relate to a projection.

          To rephrase my original question, I guess I am looking for some description of what the matrix in Qt means geometrically, and when one might need to modify its value, etc.

          Pl45m4P 1 Reply Last reply
          0
          • B Bob64

            @Pl45m4 thanks for the suggestion. A quaternion is effectively a 4D vector, so if there is any connection with the 4X4 projection matrix I suppose the columns might be quaternions. As I say, I am quite new to this stuff, but my impression is that quaternions tend to be used to represent rotations, and I am struggling to see how that might relate to a projection.

            To rephrase my original question, I guess I am looking for some description of what the matrix in Qt means geometrically, and when one might need to modify its value, etc.

            Pl45m4P Online
            Pl45m4P Online
            Pl45m4
            wrote on last edited by
            #4

            @Bob64

            Got confused by Vector4D and Matrix4x4. Sure, a quaternion is a+ib+jc+kd

            Here is probably one of the best explanations you will find out there :)
            It's Unity, but the 3D stuff is the same, but better check what your values look like.

            https://answers.unity.com/questions/1359718/what-do-the-values-in-the-matrix4x4-for-cameraproj.html


            If debugging is the process of removing software bugs, then programming must be the process of putting them in.

            ~E. W. Dijkstra

            B 1 Reply Last reply
            1
            • Pl45m4P Pl45m4

              @Bob64

              Got confused by Vector4D and Matrix4x4. Sure, a quaternion is a+ib+jc+kd

              Here is probably one of the best explanations you will find out there :)
              It's Unity, but the 3D stuff is the same, but better check what your values look like.

              https://answers.unity.com/questions/1359718/what-do-the-values-in-the-matrix4x4-for-cameraproj.html

              B Offline
              B Offline
              Bob64
              wrote on last edited by
              #5

              @Pl45m4 thank you very much. I will need to take some time to digest it properly but based on a quick skim that looks like it is very good information.

              1 Reply Last reply
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