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Summary of C3D responses

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  • Summary of C3D responses

    Thank you to all those who took the time to respond to my enquiry. The
    responses showed that we are not alone in our problem, and it seems
    at least one commercially availiable solution to this problemn is in
    the pipeline(Ed Cramp at MLS). My apologies for the length of this
    posting, I did not want omit anything that my be of use to list
    members. The main responses were as follows:
    Speaking of .c3d files, is there any Visual Basic code to read and
    write .c3d files publicly available?

    Theresa Foti, Ph.D. Shriners Hospitals for Children 950 W. Faris
    Road Greenville, SC 29605 (864) 240-6289
    I read your message and figured I might be able to help. You can use
    the READC3D.M file that I constructed to develop your program, as it
    indicates to you the format of all of the data in the C3D file. I
    have attached a file (c3d.txt) that is the c3d file format created by
    Andy Dainis of AMASS which outlines the file structure. You can find
    this file with a number of other utilities that Andy Dainis wrote for
    looking at C3D files - you can find these at the following ftp site
    which happens to be the NIH Biomechanics website where you get MOVE3D:

    The only special things that you should know that isn't completely
    outlined is that MOVE3D was created to read files that are DEC VAX
    formatted binary. Secondly the number of parameters in a file is not
    indicated or fixed. I have included a note from VICON to indicate how
    to read or stop-reading parameters!:

    "Regarding the parameters, it is easy to get confused. The record
    count you are referring to (byte 3 of the parameter section in the
    file) actually indicates the number of 512 byte 'file' records
    allocated to the entire parameters section. Because of a
    mis-interpretation of this value, Vicon software prior to version 2.6
    sometimes writes an incorrect value in here so it should not be relied
    upon anyway.

    There is no count stored for the number of parameters in each group
    and, according to the original C3D specification, all group and
    parameter records can appear in any order. This means that parameters
    could even appear before the group that they are in. In practice,
    Vicon always writes the data out with a group followed by all of its
    parameters before going on to the next group.

    The way to relate parameters to groups is by use of the group ID
    number. Our documentation is rather unclear on this so you would be
    better referring to the AMASS documentation from Andy Dainis (part 11,
    section 2.3 of May 5, 1994 manual set). Group records have unique ID
    numbers within the file which are stored as a negative value in byte
    2. All parameters belonging to the group store the same ID as a
    positive value, also in byte 2. Having found the group you are
    interested in, you need to search through all the other records to
    find the corresponding parameters with a matching ID. The end of the
    parameter data section is found when the number of characters for the
    group/parameter name (byte 1) is zero. One thing to note is that you
    can't rely on the group ID being the same for the same group in
    different files, or even successive saves of the same file, though in
    practice, Vicon tends to use the same numbers."

    With this information. The creation of a C3D file should not be a
    problem. It is somewhat difficult to reverse engineer the file
    structure without this information.

    Regards and best of luck,

    Alan Morris
    Research Engineer - Gait Lab
    Bloorview MacMillan Centre
    350 Rumsey Road
    Toronto, Ontario
    Tel (416) 425-6220 x3508
    Fax (416) 425-1634
    I am quite interested in the issues you have raised. I used MOVE3D
    during my graduate work with c3d files from a VICON system. I have
    recently purchased a Peak Motus system and would like to use the same
    routines I developed in MOVE3D to analyze my new data. I have
    recently contacted Edmund Cramp, who knows a good bit about c3d files,
    and he said he has worked on such a conversion (Motus output to c3d
    format) but was slowed by the many file formats Peak uses. Please
    send me a list of the specific file types from Motus (e.g. 3D data,
    analog, etc.) you are interested in converting, and I will forward
    this list to Edi to see what he might be able to do. Also, please keep
    me posted on whatever else you hear and any progress you make.

    Mark D. Geil, Ph.D.
    Center for Human Movement Studies
    Department of Health and Performance Sciences
    Georgia Tech
    Atlanta, Georgia 30332-0110
    Phone: 404-894-9993
    Fax: 404-894-7593
    As you know, Motion Lab Systems has written and sells "C3dEditor" - a
    program that support manipulation and editing of all the current C3D
    file formats (DEC, PC, SGI with INT or FLOAT data). Recently been
    asked by several people to produce a method of generating C3D files
    from Peak data. We are looking at this right now and I expect to have
    a method to do this within a few days. At Chris Kirtleys suggestion
    we're probably going to modify the C3dEditor to accept column data
    pasted in from another application - Excel seems to be the most

    Since you're apparently already using the evaluation version of the
    C3dEditor all you'd have to do would be download the new release when
    we get the feature implemented.

    If you'd like to send me a couple of the C3D file that you have
    produced (the ones that aren't working) I'd be happy to have a look at
    them and see if I can figure out where the problem is ...

    Edmund Cramp,
    Motion Lab Systems, Inc.
    4326 Pine Park Drive,
    Baton Rouge, LA 70809 USA
    +1 225 928-4248 (voice, 2 lines) Note - New Area Code!
    +1 225 928-0261 (fax)
    My email address is
    For information about Motion Lab Systems please visit our web site at
    I am currently writing a piece of software to convert ASCII text files
    in the format

    video frame 1 marker1_x marker1_y marker1_z marker2_x marker2_y
    marker2_z... video frame2.... ... analog sample 1 analog_channel1
    analog_channel2... analog sample 2 ...

    into c3D files (suitable for input into Oxford Metrics 'Bodybuilder'

    The software is written in Visual Basic 5- it is at the final testing
    stage and I hope to complete it this week, perhaps next, depending on
    other commitments.

    I am happy to make the executables available, or to share the source

    Ben Heller (PhD), Clinical Engineer Medical Physics and Clinical
    Engineering Royal Hallamshire Hospital Sheffield UK
    You must be telepathic! This is exactly what I am trying to do at the
    moment. I spent all of Sunday trying to write c3d format files using
    MATLAB, and finally gave up! The binary is just too complicated - you
    only have to make one small mistake and Vicon rejects it.

    I've been in touch with Ed Cramp at MLS and he's presently having a go
    at implementing a cut and paste function into his C3Deditor, which
    will at least be a temporary solution. In the long run, as you say, it
    would be nice to be able to import from a file, but he thinks this
    will be a lot more tricky to implement.

    There's also a small snag in that the price of the C3Deditor is

    Dr. Chris Kirtley MD PhD
    Dept. of Rehabilitation Sciences
    The Hong Kong Polytechnic University
    Hong Kong
    Special Administrative Region of The People's Republic of China

    Tel: +852 2766 6755 Fax: 2330 8656
    PolyU Gait Lab:

    Clinical Gait Analysis:
    Thanks again to those who responded. Any further information or
    responses would be most appreciated.



    ************************************************** **********************
    Gerome Garthwaite
    Biomechanics Post Graduate Student
    University of Otago
    School of Physical Education
    PO box 56
    New Zealand.
    E-mail -
    Phone (W) - 00 64 3 479 9117
    (FAX)- 00 64 3 479 8309
    ************************************************** **********************

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