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GPS Performance analysis

Discussion in 'Boat Electronics' started by Alberto \(Tilax\), Jan 20, 2005.

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  1. I'd like to analyze GPS data with some sort of software helping to learn
    something about my regattas.
    I've found just GarTrack. It's very very simple and most of all accept just
    a strange file format (gardown)
    The results is that I cannot get neither convert (many hours spent on
    Internet) my data to something GarTrack could be feeded with.

    Do you know something better than GarTrack that, also, can accept a more
    widely available file format?

    Thanks for helping.
  2. Jack Painter

    Jack Painter Guest

    Did you mean "speed over the ground:"?

    Not sure how it helps to know a measured-log calculation of 10kts when the
    tide and current might be holding you to 5kts over the ground ;-) If you
    know your boat's hull speed under various sails and points off the wind you
    could estimate current from speed (vector) over the ground, but not the
    other way around given only speed through the water, which would include an
    unknown vector of current direction.

  3. Alan Murphy

    Alan Murphy Guest

    Much will depend upon the exact file format that you have. You could
    try "GPS Utility" and the Import File Converter that is available on The Import File Converter is designed for dealing
    with large varieties of text format files (e.g. *.csv) and converting
    them for use in GPSU.

    I hope that helps.
    Alan Murphy (author GPSU)
  4. I assume you are talking about a sailing regatta?

    Obviously you're right.
    It's just a money issue.
    I'm taking a step at a time: GPS first, relative wind as a second step
    Hope it would not be the usual tracking SW. There are alot not so useful for
    the deal.
    GarTrack (even if I don't like it) could import GPS data (just if I could
    have the right file format) and then it let me enter wind data manually.
    So not a great thing but I could be enough as a fice step

    Already tried.
    I can convert almost anything but what I need :-(

  6. Did you mean "speed over the ground:"?

    I confirm what Wayne sais.
    I'm interested in speed against water... the only thing helps in trimming
    the boat.

  7. Jack Painter

    Jack Painter Guest

    Understand wrt sail trim, and those are the known characteristics of a boat
    that I referred to. When I raced in the Great Lakes, speed through the water
    was a good evaluator of trim. Not enough information in the Chesapeake Bay
    though, when currents are a major factor.

    Velocity = speed + direction. To evaluate the effectiveness of a course to
    mark, speed through the water is not relevant, and SOG from a GPS is still
    only part of the equation, it requires an additional computer calculation to
    determine effective VOG, that is; Course Made Good + SOG.

    On a visual bearing to the next mark as a lay line, within a minute of
    averaging time, most computers will settle at a reliable Course Made Good,
    which is velocity over ground adjusted for the effect of currents and slip.
    This also allows a calculation of time to mark. SOG however is instantly
    available (a few seconds delay at most) and is more relevant to verifying
    the known performance standards of sails, trim, degrees off the wind and
    speeds that result from this. If current is dragging you to weather for
    instance, then more heel (allowing more slip) could maintain best speed over
    the best course to the mark. Historical GPS tracks around a course do not
    tell the story it took to get there. Neither could speed through the water
    by itself help trim the boat for best course to a mark that you won't
    achieve without more information.

    Jack, who was a Gary Jobson fan for about 25 years.
  8. Jack Painter

    Jack Painter Guest

    He's apparently doing well ater the second-round/bout last year. Here is his
    lecture schedule:

    Best regards,

  9. Daniel

    Daniel Guest

    Any idea of what is the format required by GarTrack?
    Are the files binary or ascii? If you have the specs, a small program in
    C could solve the problem; I may have some suggestions if you like but
    first of all I need to understand the specs of the requested input files.

  10. Willem Amels

    Willem Amels Guest


    Have a look at TacticTool at

    I developed this specifically for sail racing and outputs data in text
    format. Also it has many features for doing analysis within the program
    eg. stripcharts and polar diagrams, although the polar functions require
    wind input.


    Willem Amels
    (Author TacticTool)
  11. Have a look at TacticTool at

    seems really something very usefull and very near to what I'm looking for.
    I've big trobles on my pc (hope monday I can have che HD changed) so I'm not
    downloading the beta.

    Can it be feeded with nmea prerecorded file?
    I know it's quite punishing but... wind data can be fed manually?

    Pls, can I know the price in email?

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