Question with Elevation Gain - Yes I read HelpFile

[Coke]

I have read the “The TopoFusion Climbing Analysis Dialog” Help page.  I have also searched the forums which I found helpful.

I do have a question about a elevation gain/loss relating to a recent track that I made out while hiking.

My question is… Why is the Straight GPS value so crazy?  I hiked in the desert and my max elevation was 5748.

Here is what I get when I run the “Climbing Analysis”
----------------------------
No DEM (elevation) data, use Download DEM Data button.
TopoFusion:       21401 ft
Straight GPS:       26365 ft
Straight DEM:           0 ft
Maptech:           0 ft
TopoUSA:           0 ft
Custom Algorithm:       21401 ft
-----------------------------

These values seem insane to me.  I know my Garmin 60CSx barometric sensor was correctly calibrated recently, albeit not in the desert.

While, on the “Climbing Analysis Window” I clicked on “Download DEM Data for track”, then I made data source: DEM, and set minimum gain to:1 (meter) and here are the updated results:
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TopoFusion:       21401 ft
Straight GPS:       26365 ft
Straight DEM:        7209 ft
Maptech:        3074 ft
TopoUSA:        7209 ft
Custom Algorithm:        6675 ft
------------------------------

This value of 6675 seems reasonable to me based on my experience for that day.  I did those adjustments based on a recommendation of another forum member.

Here is a link to my data if someone wants to take a look and provide some help.

Link to my Track Data

You may need to do a "right-click save as" on the link.

Thanks,

Nick

[Krein]

Wow.  Those numbers look like they are from a forerunner 205/305.  Definitely whacked.

The problem is just too much variability from point to point.  The profile looks fine from far out, but the climbing accumulates rapidly.  Try using the custom algorithm with a minimum gain of 10m.  That reduces it to normal, and is likely what the GPS should be doing itself.  I'd check your firmware and see if a more recent version doesn't give you a better profile.

[Coke]

Thanks for responding.  The unit has the latest firmware and other hikes that I have done when loaded into TF appear to be fairly accurate.  

This last hike I was doing had an incredible amount of boulder hopping, ups and downs for hours.  I am wondering if all that jumping around somehow whacked the stats.

Something else I find puzzling about this...

My GPS has a "Trip Computer" which I reset prior to going on the hike.  Upon arrival at my car it reported 7890' of total Assent and 16.3 miles of travel.

How then when I analyze the track in TF it gives that wildly inflated value?

Thanks for your help and I hope I don't sound critical of TF. TF is the best analyzing software I have ever seen for track data.

[Krein]

I don't think the boulder hopping had much to do with it, but it's possible.

My guess is there's a problem with that latest firmware.  I see several places where the elevation drops 30 feet only to go right back up on the next (very close) point.  Especially when you weren't moving this was happening.  That's why the "TopoFusion" algorithm was showing lower numbers -- it throws out times when you weren't moving.

We don't know what the garmin internals are doing, but I highly suspect they are doing something like "min gain 10m" on the computation for total gain in the Trip Computer.  On my 60CS (non-X) the numbers there are actually conservative, in my opinion.  And they ALWAYS differ from what the actual straight-up sum of the GPS track elevation is.

Hope that helps.

Not taken as critical of TF at all -- TF is only as good as the data handed to it, in this case.

[Coke]

Thank you for your detailed and through explanation.  It helps immensely!

Your contribution in these forums is a huge credit to TF.

Thanks again.