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  • Summary: query on GPS systems

    Summary of query on Global Positioning Systems (GPS):

    ORIGINAL QUERY:

    We have a project to investigate the biomechanics and dynamics
    of automobile driving around a driving track. We need measures of
    vehicle position. We think we could use GPS to obtain an *accurate*
    measure of position over time (using data-logging). As off-the-shelf
    GPS (e.g., for hiking) is of no use (accuracy approx. 30 m), we will
    need to buy a Differential GPS (DGPS) system that can provide
    sub-meter accuracy at rates in excess of 1 Hz (more like 5Hz). But
    they are pricey.

    Has anyone out there dealt with this problem? If so, I would be
    grateful to receive any information on suppliers, technical
    specifications, and of course, prices. I shall summarize for
    Biomech-L the replies. Note, GPS and related technology is likely to
    be the "wave of the future" with regard to obtaining in-the-field
    kinematic measures of the control and coordination of everything from
    geese to footballers to space planes - probably in the not too distant
    future...

    Thanks,
    Paul

    ----------------------------------------------------------------------

    REPLIES:

    From: Peter Sinclair

    You might try contacting someone from Aeronautical engineering at
    Sydney Uni. I remember meeting someone there who was using
    differential GPS to control unmanned aircraft. They claimed to have
    enough resolution to control the pitch of the plane by mounting a GPS
    module on each wing and comparing the calculated height above ground.
    Unfortunately, I can't remember who I was talking to. You will have to
    send a general inquiry to someone in that department
    (http://www.aero.usyd.edu.au/).
    School of Exercise and Sport Science
    The University of Sydney
    ----------------------------------------------------------------------

    From: Richard Smith

    That's not true. My six degrees of freedom
    inertial segment datalogger will do the same for every segment!
    Range/price: 2 km range at $25k.
    Faculty of Health Sciences
    The University of Sydney
    ---------------------------------------------------------------------
    From: Ben Hale

    A cheap solution that might or might not
    work: if you have two recording devices available- you might get by
    with two of the cheaper, non-differential units. Just have one
    stationary and one in the moving vehicle, and take the difference
    between the two to get rid of the offset.
    Hopkins Marine Station
    Oceanview Blvd. Pacific Grove, CA 93950 Lab: (831) 655-6208 Home:
    (831) 372-4519
    ---------------------------------------------------------------------
    From: "Gunter Siegmund"

    We have used DGPS to monitor vehicle position in
    a study of long-haul truck driver fatigue. A description of the
    methods is given in a technical paper (see citation below) and is
    available through the Society of Automotive Engineers (www.sae.org).
    Our study was conducted back in 1993, so I don't know whether this
    information is stale or not. In brief, we used three Trimble Land
    Surveyor 4000SE receivers: one as a base station and the other two as
    rovers on two different vehicles. Sampling was limited to 2 Hz. We
    rented the equipment because at the time this technology was still
    expensive (Can$10,000+ for the equipment we used). Long
    post-processing times were needed (about 2.5 times the duration of the
    test), however newer PCs and GPS equipment have no doubt reduced this
    time. We were able to resolve displacements of about 2-3 cm and
    successfully used the data to monitor both vehicle following distances
    and lateral position of the vehicle within the lane. We conducted our
    study on an airport runway and therefore has no trouble remaining in
    contact with the satellites. The more satellites you can "see", the
    better the resolution of your measurements. In '93, we had to plan our
    tests based on the number of satellites which remained at an altitude
    of about 15 degees above the horizon for the estimated duration of our
    tests (max ~ 4 hours). Presumably there are more satellites now and
    this will be less of a problem. King DJ, Siegmund GP, Montgomery DT
    (1994). Outfitting a Freightliner tractor for measuring driver fatigue
    and vehicle kinematics during closed-track testing (paper no. 942326).
    Warrendale, PA: Society of Automotive Engineers.
    Biomechanics Lab,
    School of Human Kinetics University of British Columbia, Vancouver,
    BC, Canada http://www.hkin.educ.ubc.ca/pages/biomech.htm
    Principal,
    MacInnis Engineering Associates 11-11151 Horseshoe Way, Richmond, BC,
    Canada, V7A 4S5 http://www.maceng.com
    ---------------------------------------------------------------------
    From: Trimble NZ Support

    I have forwarded your email to Herga
    Instruments, our dealer in Queensland. They should be able to give you
    an idea of what Trimble GPS products are available and their prices.
    If you want to contact them yourself their contact details are:
    Herga Instruments 33 Allison Street Bowen Hills, QLD 4006 Australia
    Ph +61 7 3852 1245 Fax+61 7 3252 1275
    ---------------------------------------------------------------------
    From: "Philippe Terrier"

    Our group utilizes GPS technology to study
    human locomotion since 1997: Schutz Y, et al. Could a satellite-based
    navigation system (GPS) be used to assess the physical activity of
    individuals on earth? Eur J Clin Nutr. 1997 May;51(5):338-9. 3 other
    papers are "in press", read carefully the "literature update" in
    biomech-L ;-) You can find some indications about one of our current
    projects at http://dgrwww.epfl.ch/TOPO/recherche/recherche3.htm. It is
    possible to assess position with a centimetric accuracy by using for
    exemple Leica 500 system (5Hz measurment frequency) or Ashteck Javad
    (10Hz (20Hz implemented but not functional now)). This device is the
    best actually in the market: it use both Navstar and Glonass (russian)
    satellites, work at high frequency, is relatively lightweight (2.5
    kg), can resolve the ambiguities very fast (no static initialisation).
    You can directly obtain Doppler speed with an accuracy better than
    0.6cm/s. Data are stored on PCMCIA memory card, but you can also work
    "on line" with differential correction transmitted by FM. One
    drawback: always keep in mind that GPS receivers need to directly
    access to satellites (4 minmum, but 5-6 for high precision): a tree
    can stop the signal ! Of course you need two GPS receivers to perform
    differential carrier phase recording. It's very expensive (30000$),
    but you can find 1Hz receiver recording differential smoothed code
    with an accuracy of a few meter for less than 1000$...
    Insitute of Physiology, Lausanne, Switzerland
    ---------------------------------------------------------------------
    From: Dieter Rosenbaum

    You should contact Ewald Hennig (if he does not
    respond directly) at: ewald.hennig@uni-essen.de
    Funktionsbereich Bewegungsanalytik
    Movement Analysis Lab Klinik für Allgemeine
    Orthopaedie - Orthopaedic Department Westf. Wilhelms-Universitaet
    Muenster - University of Muenster Domagkstr. 3 D-48129 MUENSTER
    Germany
    ---------------------------------------------------------------------
    From: Ewald Hennig
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