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Some observations regarding the origins of the DLT.

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  • Some observations regarding the origins of the DLT.

    Dear Biomch-L readers:

    I am just beginning to catch up with my E-mail after a two week
    vacation, and I have just encountered Ton van den Bogert's recent
    discussion of the DLT--and it's origins. Although Ton's statements
    are generally correct, the DLT was in use in photogrammetry long
    before Abdel-Aziz and Karara gave it a name ("The Direct Linear
    Transformation') in 1971.

    As some of you may know, I have worked on 3-D tracking algorithms
    since 1968. My first paper on the topic was prepared in 1970--
    a Master's Thesis for Michigan State University entitled
    "Photographic and Computational Techniques for Three-Dimensional
    Location of Trampolinists."

    In the 1970's, while Karara and his students were developing the DLT
    at tne University of Illinois, I worked at Penn State and at
    Stanford on algorithms I described as the generalized
    three-dimensional model, and the generalized two-dimensional model.
    Some of this work was presented during the International Congress of
    Sport Sciences, which was held in Edmonton, Alberta, in 1978. A
    more complete reference is my doctoral dissertation, "Close-Range
    Cine-Photogrammetry: A Generalized Technique for Quantifying Gross
    Human Motion" (Penn State, 1981).

    Since 1981, I have continued my interest in image-based motion
    measurement, but I have chosen to pursue the technology in a more
    commercial/industrial setting, while others have investigated
    the topic in academic environments. I have applied the technology
    in a wide variety of military, industrial, academic, biomedical,
    legal and life science environments.

    The purpose of this note is to point out that the DLT has a variety
    of origins that extend back beyond the work of Abdel-Aziz and
    Karara. This is not to negate their excellent contribution, but to
    let the biomechanics community know that they were not the first to
    use this algorithm.

    Over the last twenty years I have developed an extensive
    bibliography on the topic. Although I don't have the time at the
    present to trace all the references I have on DLT-like algorithms,
    I can cite one in particular, in the photogrammetric literature,
    which provides an explicit description of the DLT ...

    Das, G.B. "A Mathematical Approach to Problems in Photogrammetry,"
    Empire Survey Review, Vol X, No. 73, July 1949.

    This was written 22 years before Abdel-Aziz and Karara--by a Brit.

    Frankly, I believe that the reason the DLT did not take-off until
    the 1970's was the lack of computing power. The algorithm had been
    around for a while, but the ability to exploit it did not
    exist until practical computer software had been developed.
    However, the people needing the capability (Abdel-Aziz and Karara,
    myself, and others) were apparently unaware of the algorithm and so
    we 'reinvented the wheel' and then wrote the software. Likewise,
    in other disciplines, the same 'wheel' has been reinvented.

    I hope this has provided food for thought.


    Jim WALTON
    4D VIDEO
    3136 Pauline Drive
    Sebastopol, CA 95472

    Phone: 707/829-8883
    FAX : 707/829-3527