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3D visualization of GRF !

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  • #1

    3D visualization of GRF !

    Dear Biomch-L Members,

    I would like to visualize in 3D the GRF vector as it results from one AMTI force platform data. Could you help me with any suggestion, including an open-source software ? It is important to have the option to automatically read the AMTI's data files [.txt or .asc]. I have some results with FreeMat but I would like to see other solutions !


    Thanks in advance,
    Daniel
    Tags: grf, vector
  • #2
    Re: 3D visualization of GRF !

    Daniel,

    please have a look at CONTEMPLAS TEMPLO. Version 5.0 already includes features to visualize the GRF vector with one or more cameras. The vector is visualized as an overlay during AVI playback.
    The next release (coming soon) will also have a REALTIME vector display in multiple cameras which can be used as a feedback system.

    TEMPLO supports AMTI as well as Kistler, Bertec or other 3 component force platforms.
    For this special application you might use a USB webcam, but we recommend high-speed and high-resolution industrial and/or HDV cameras.

    Best regards,

    Thomas.

    Comment

    • #3
      Re: 3D visualization of GRF !

      Daniel,

      There is an open-source software named Mokka (http://b-tk.googlecode.com/svn/web/mokka/index.html) which gives you the possibility to visualize GRF in 3D. However, it doesn't support (not yet?) AMTI files (txt, asc). Could you post some of these files to see if it could be possible to load them?

      Best regards,

      Arnaud

      Comment

      • #4
        Re: 3D visualization of GRF !

        See http://c-motion.com/ for commercial option. it imports AMTI Force Platform data in ASCII format and has flexible pipe-line to convert that into GRF by applying Force Platfrom specific computations, provided you have all the required parameters like Corners, Calibration Matrix, Geometry information etc. and visualize. A script to directly import AMTI Analog ASCII data into a C3D file is available. Other available scripts can be used to modify the parameters and locate the corners. For free software alternative, https://simtk.org/home/opensim also can visualize GRF but it accepts only MOT format Force/analog data.

        Comment

        • #5
          Re: 3D visualization of GRF !

          Originally posted by abarre66 View Post
          Daniel,

          There is an open-source software named Mokka (http://b-tk.googlecode.com/svn/web/mokka/index.html) which gives you the possibility to visualize GRF in 3D. However, it doesn't support (not yet?) AMTI files (txt, asc). Could you post some of these files to see if it could be possible to load them?

          Best regards,

          Arnaud
          Thank you all for your answers !
          I know Mokka but, as you said, it doesn't support AMTI files ! I've seen only .gr files [force platform] and I don't know this format ! I've attached 2 files [force and COP coordinates] which originally are .asc files. It will be very interesting for me if you'll succeed to vizualize with Mokka !

          Regards,
          Daniel
          Attached Files

          Comment

          • #6
            Re: 3D visualization of GRF !

            Daniel,

            A bug report was filled to support AMTI files in Mokka (issue 25) and an implementation has already been proposed (see comment #1 for the issue 25 and the screenshots joined with the comment).

            However, one question still need to be answered: Do you know if the data in the file FxFyFzMxMyMz correspond to the data measured by the sensor (origin of the force platform) or the data acting at the center of pressure? The implementation proposed in Mokka assumes the first case. If it is not, then the code must be adapted in consequence.

            Finally, for your information, the GR* files are(were) used by the company BTS Bioengineering with the motion capture system Elite.

            Regards,

            Arnaud

            Comment

            • #7
              Re: 3D visualization of GRF !

              Dear Daniel,

              you could do this within the Simi Motion package from Simi. Unfortenatly it is not cost free..
              You can overlay the 3D vector on the video or display it in 3D graphics. AMTI plates are supported. You can watch several videos here http://www.youtube.com/user/SimiSystems

              Philipp
              Last edited by Philipp Ruß; February 6, 2012, 06:51 AM.

              Comment

              • #8
                Re: 3D visualization of GRF !

                Thank you all for your answers !

                Daniel

                Comment

                • #9
                  Re: 3D visualization of GRF !

                  Hi Arnaud,

                  If I have a good understanding of the AMTI documentation, the force and moments are calculated by the sensors [AccuGait Platform which I'm using]. In the same time the COP is
                  calculated only from the Mx and My moments and the Fz force .
                  -One question is how exactly Mokka compute automatically the COP ? [ as I don't have access to the cited reference : PWA (Zatsiorsky - Kinetics of human motion - 2002)]
                  -The second question is how Issue 25 is implemented in Mokka because I don't have experience with this kind of activity !

                  Thank you !
                  Regards,
                  Daniel

                  Comment

                  • #10
                    Re: 3D visualization of GRF !

                    Hi Daniel,

                    The computation of the PWA (point of wrench application) uses all the components of the forces and the moments measured by the sensors. So, the computation of the PWA doesn't assume that horizontal forces (Fx,Fy) are negligible, and then this calculation should be more accurate when computing joint kinetics. However, for gait analysis, the difference is low.

                    The following link gives you the formulas and the differences between the PWA and the COP: http://books.google.ch/books?id=wp3z...page&q&f=false

                    The implementation of the issue 25 is based on the forces and moments stored in the FxFyFzMxMyMz file and the geometry of the force platform (given by the user). The use of the geometry is twofold. First it is used to display a rectangle representing the force platform in the 3D space. Second, it computes the matrix between the platform frame and the laboratory (global) frame. From this matrix, the FxFyFzMxMyMz data are expressed in the global frame and then used to compute the PWA. The ground reaction moments acting at the PWA are computed (same computation than if you use the COP). The final result is the display of the GRF in 3D acting at the point of application.

                    So the user has to give the geometry (corners and origin) of the force platform expressed in the global frame. But to simplify that, it is possible to give only the dimensions of the force platform (Width x Length x Height), then Mokka computes automatically the corresponding geometry (assuming the force plate is in the ground and the origin is at the middle of the height). You can find the dimensions in the AMTI documentation. By default Mokka uses the dimensions of the AMTI OR6-7 force platform, but if you set other dimensions, they will be stored automatically and reloaded the next time you open an AMTI file. For the Accugait platform, and based on the technical drawing, the dimensions to give will be 501.7 x 497.8 x 43.1 mm

                    Regards,

                    Arnaud

                    Comment

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