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  1. #1
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    Looking to purchase a gps bike computer, need advice

    First off, I'm a research assistant at a university working on a project that needs to use a GPS device to accurately track position over time. I've found that using a bike computer is most likely our best option, but I'm having trouble finding out some of the technical aspects about the devices. Hopefully some of you can help me.

    I've been looking at the Garmin Edge 305 because its can upload its data to the Garmin Training Center. First off, I'd like to know if the files that the Training Center uses are encrypted in any way. We need to be able to interpret the data in these files with our own programs.

    Also, I'd like to know if there's any way to set the bike computer to update the file for the Training center at a regular interval, say about every second or 2. They sent me a screenshot of the program, but the data was not updated at regular intervals, which is very important to this project.

    Oh, when I say that the GPS needs to be accurate, I'm thinking to within <10 feet.

    If anyone knows of any bike computers that can accomplish what I need it to (accurate to within 10 feet, update position/velocity/time data every second, non-proprietary data), please feel free to make suggestions.

  2. #2
    NEPMCPMBA President
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    Quote Originally Posted by FlashBronzer
    Oh, when I say that the GPS needs to be accurate, I'm thinking to within <10 feet.
    Reliably?

    None.

    I don't think any civilian GPSr can get you repeatable results to within 10 feet. I think WAAS receivers claim their BEST as +/- 3 meters.... and by my experience, thats just not repeatable. One point could be 3 meters, another could be 10.

  3. #3
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    Oh there's plenty of civilian GPS receivers that get that sort of accuracy, but how much are you willing to spend on one?

    The most important question we need answered is which software you're going to be using for your project? Some garmins will work, but won't give you the accuracy you ask for reliably. If funding is limited, they're probably your best bet, however. Personally, I'd recommend a handheld model with an external antenna like the 60CSX or 76CSX. The external antenna will give you far better reception than the built-in antenna. They also will interface with MN DNR Garmin (freeware) which will easily convert your GPS files into .shp format which is the most commonly used format for geospatial vector data.

    If the sort of accuracy you mention is really what you need, then you need to consider survey-grade equipment (usually Trimble). Some Trimble receivers get sub-centimeter accuracy and Trimble's .ssf data format allows you to post-process your data in the lab with reference data from fixed base stations. The Windows Mobile models running ArcPad even give you the ability to build and update geodatabases, which are really useful if you're managing large datasets.

  4. #4
    NEPMCPMBA President
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    Quote Originally Posted by NateHawk
    If the sort of accuracy you mention is really what you need, then you need to consider survey-grade equipment (usually Trimble).
    Can they maintain their accuracy while being mobile? I thought they needed to be stationary for that kind of repeatability...

  5. #5
    American Icon
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    What type of research?

    If you need it to record data every second or two, and be accurate to <10 feet, that is asking quite a bit from a small bike unit.

    The 60Csx is a great unit and may be up to the task a bit better, but it is of course a larger handheld unit.

    Perhaps you should call garmin directly. Some of the best customer assistance I have come across.

  6. #6
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    Quote Originally Posted by RoyDean
    Can they maintain their accuracy while being mobile? I thought they needed to be stationary for that kind of repeatability...
    Sure they can. Now granted if you're collecting point data (or route events), the longer you stay in one place for them to average, the more accurate you're going to be. But Trimble doesn't sell the backpack-mounted receiver/mast antenna that attaches to the Recon handheld datalogger for nothing. It's the post-processing ability once you get back to the office that really excels, though, because you can correct for the vast majority of atmospheric distortions that way.

    Still, they do have the capability to be quite accurate while being mobile. You just need a better receiver than the Juno (which, BTW, is less accurate than my 76CSx, in spite of all the cool features it has).

    For many folks, one of the high end garmin mapping receivers is plenty sufficient. Lots of agencies use them. You just need to assess how much accuracy you TRULY need. If 15-20ft is okay (seems to be about average for me), then a Garmin handheld would work well for you. However, if you'll be doing calculations based upon a GPS position, then you're going to want the most accurate receiver you can afford.

    BTW, I'm very surprised that as a university student, you don't have access to SOME kind of survey grade receiver...even an old Trimble GeoExplorer 2 or 3. I went to a small private undergrad institution several years ago that had a number of those available for students to use (who were working on projects). I'm at a medium-sized university now and we've got a lot of survey grade receivers that students are permitted to check out for their research projects (you just assume financial liability if you do something stupid and break/lose one).

  7. #7
    The plough
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    Regarding what you need, I think a GPS data logger is more than sufficient.

    I bought one at the recent Taipei Conputex computer show for about USD 50. It has 32 MB of RAM, can store 200 000 coordinates and you can set it to record the position from every second+ or every distance interval. The data can be exported directly to Gogle Earth, or to any other mapping software as it can save the data in several formats.

    It has 51 receiving channels and a Bluetooth facility so it can act as a GPS receiver for a Bluetooth enabled laptop or smartphone with GPS software. The logging is accurate enough to be able to overlay my path directly on the road on Google Earth and show WHICH side of the road I was traveling (outbound vs. return trip).

    If anyone is interested in this, let me know and I will try to find out from the manufacturer if they can sell to public and for how much.

    V.

  8. #8
    Scott in Tucson
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    Quote Originally Posted by FlashBronzer
    First off, I'm a research assistant at a university working on a project that needs to use a GPS device to accurately track position over time.
    Hey, I'd be curious to hear more about the research you are doing. Are you tracking / modeling cyclists? Just wondering because I've done some work along those lines at university.

    Sounds like the Edge may work for you. To answer your question, you can get .TCX files from Training Center, which are not encrypted. They're just XML and the spec (a little outdated, but there) is on garmin.com.

    You can also set the Edge to record once a second, so you are covered there. Now, why do you need 10ft accuracy?
    Author of TopoFusion GPS Software. MTB+backpacking = bikepacking.net. Ride Diary.

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