Elevation Values

[Brent]

I have a Dakota 20.  I am getting differing values for the total ascent that my gps is displaying to what value TF is giving me in the Climbing Analysis tool.  The Straight GPS value TF gives me is over a 1000' difference (1000' gain).
There appears to be a difference for every track I download to TF.

Why the difference and which do I use to determine the total climbing I have done?

Thank you.

[ScottMorris]

Most Garmin GPS's are a little too conservative when it comes to reporting total gain, IME.  This page might help describe some of the issues:

http://topofusion.com/climb.php

In general it is very hard to get any GPS/software combo to match up exactly. Best thing is to find one you like and then stick with that for consistency and comparison.  But it's a can of worms, for sure.  Take any "this ride has XXXX feet of climbing" claims with a grain of salt.

[Brent]

What I don't understand is why isn't the Straight GPS value exactly the same as what my gps is indicating?  I understand why other analysis types are different, but isn't the Straight GPS value the data that the other methods are using to get it's values?  If so, then I would assume that this would be the number that the GPS has gathered as the Total Ascent.

BTW, great blog.

Thanks again for the clarification.

[ScottMorris]

Right, so the GPS has its own algorithm for computing elevation gain based on the points it records.  In general they are more conservative than just adding up the change in elevation in the points (which is what "straight GPS" is).  The algorithm they use also sometimes changes with different firmware releases.  Make sense?

[Brent]

So is TF pulling "raw" data (elevation values) at each lat. and lon. that is recorded before the gps applies its algorithm that is being displayed to me?  If so, where are these values and can they be viewed or is this the the Straight GPS value?

Maybe I am analyzing this too much , but I just want to understand the process.

[ScottMorris]

Yes, TF gets the raw values and that's the straight GPS number.  Though the GPS will also be using elevation values per second for its number, and depending on your tracklog setting, you may or may not be recording every second.  So there's that too.

No worries on the Q's, there are some subtleties to it.

[Brent]

Thank you for taking the time to address my ?'s.