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  1. #1
    mtbr member
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    Nov 2009
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    accurate elevation data

    i got a forerunner 305 and i think the elevation stuff is not very accurate and didn't know if there was software i can upload my data to that would maybe be able to correct it some... i did a 25 mile ride and it said i climbed 7600ft which i guess would be insane if the data was correct. i do have my device set to record every second and i used a speed/cadence sensor with it. any advice would be appreciated.

    thanks,
    adam

  2. #2
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    Reputation: NateHawk's Avatar
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    Dec 2003
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    11,503
    many sharing websites will do elevation corrections. Garmin Connect does it automatically if your device lacks a barometric altimeter.

    But even still, elevation measurement is nearly as much of an estimate as calorie consumption. Regardless of the method of measurement chosen, they're all variable over time. While a well-calibrated barometric altimeter can be pretty accurate, when you're talking about an activity that can last several hours and many miles, the accuracy will not be consistent over the entire thing. GPS altitude measurement is even less accurate because its accuracy is heavily dependent on signal quality and satellite geometry.

    The corrections typically applied basically take the GPS position of your file and extract elevations from a database. Most of them have 30m resolution, so accuracy tends to be very limited. This method is at least more consistent, but since your GPS position will vary if you do the same ride over and over, this method will produce results that vary from ride to ride.

    This topic gets discussed here fairly regularly. A good way to check your variability is to take a specific section of trail you ride often...something somewhat easy like a hill that's a consistent climb (or descent) with no undulations. Plot your track on a topo map and count contour lines between the highest and lowest points. That should give you an estimate within one contour interval of actual (contour intervals will vary depending on your terrain, check the map legend). Then compare that to the numbers your GPS gives you over the same section of trail. That should help to give you an idea of the difference between your GPS and actual.

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