The TopoFusion Climbing Analysis DialogOne issue of interest to the developers of TopoFusion is the various methods available for the computation of the total ascent along a GPS track. We often hear wildly inflated claims of XXXXX feet of climbing--and it's by GPS! But how were those numbers computed? The Climbing Analysis dialog provides a tool for comparing a number of different data sources as well as algorithms for computing the total elevation gain along a track.
The climbing analysis dialog is under the Analysis Menu. Below is a screen grab of the dialog:
The file to be analysed is selected in the dropdown box (it must be loaded in the main TopoFusion window). Below the totals for the various algorithms are listed. A custom method is available with the following settings:
Data Source -- Either GPS (from GPX file) or DEM interpolated.
Minimum Gain -- The minimum continous gain required for a climb to be
Subdivide segments -- Whether to divide segments longer than the
spacing, interpolating at "spacing" intervals if longer. TopoUSA
appears to be doing this.
Check moving time -- whether to consider elevation gained while the
GPS wasn't moving or not. TopoFusion does not count this as
legitimate gain, since it's often due to GPS error.
Presets -- sets the custom algorithm to the settings of the different
algorithms, so that it is clear what is being computed.
DEM interpolation method -- effects how DEM elevations are computed.
As far as we can tell, other programs are using bilinear. This
setting effects all of the DEM calculations, not just the custom
algorithm. It does not effect the interpolation method used for 3D
Add DEM Elevation to Track - This button will add (replacing any current data) DEM interpolated elevation values to the currently selected file. This is very useful for tracks drawn with the pencil tool.
Some observations: TopoUSA offers the most inflated climbing numbers, especially when the track is in a fairly steep (mountainous) area. In general, using DEM interpolation inflates the numbers considerably over GPS (barometric) acquired data (collected by a Vista unit). However, in flat areas the opposite is true: GPS acquired data tends to be much higher than DEM interpolated values.
What to trust, then? Well, as in any measuring process there are errors involved, and a typical way to deal with small errors is to smooth the data. This is exactly that Maptech appears to be doing by only counting climbs that are larger than 10 meters. Doing this sort of smoothing is extremely important when using DEM interpolation as the resulting profiles are riddled with noise. When looking at climb by the start and end elevation it is easy to see when DEM (and GPS elevation) is inflating it (assuming you know there are no downhills). Smoothing by something in the neighborhood of 10 meters seems to bring most climbs back to reality, though it can sometimes be to harsh to a GPS acquired elevation track.
TopoUSA is the worst of them all--subdividing individual segments while not doing any smoothing. Subdividing is not a bad idea in general, since small ups and downs could be missed by the GPS track. However, since the GPS track logging algorithm in Garmin units seems to be mindful of speed changes it is unlikely any major changes in elevation (from climb to descent or visa versa) will be missed. Also, in "most often" tracking (now always possible due to the 10K track logs), the detail is often more than sufficient to capture all significant ups and down.
The climbing numbers displayed in the main form of TopoFusion are from whatever data (usually GPS acquired) is present in the GPX file. No smoothing is currently done, however if the track has time data any segments determined to be "not moving" are thrown out--this helps eliminated many errors. It is likely that in the future TopoFusion will add a smoothing algorithm to yeild more robust climbing numbers. Our general feeling is that the current numbers are still often inflated, but not as badly as other programs (TopoUSA).