limit gradient scale in chart to something reasonable instead of autoscaling to silly values

Andrew Heard shared this idea 2 years ago
Completed

Does it make sense to autoscale the chart gradient to +/-200%? In my case (screen capture below) these are very nonsense values that Garmin Basecamp has calculated; I have no easy/ convenient control over them. Maybe limit/ clamp any outlying values to no more than +/-90%, or maybe even ignore these values? What does a value > 90 even physically mean? Maybe it could be an import setting? Only then autoscale the remainder of the values. Thank you.5fbb8acc4d8602131ce3a63325574db2

Comments (9)

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Based on this idea http://help.locusmap.eu/topic/improve-change-of-altitude-track-style-mode , I created a lot stronger filter for gradient to eliminate huge jumps based on even a small change of altitude on really short distance.


You'll see in next version, but I believe it will be a lot better now.

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Thank you - yes it looks a lot better now in 3.7.0.

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Perfect, glad to hear it.

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I just created a new track with 3.13.0/ BRouter, and mainly with fast bike profile - see attached, all normal process, but there are 3 huge negative spikes in the gradient which make the chart unusable - gradient -400% - I don't think possible (!). I won't follow that route on my bike over the cliff. It would be an additional improvement to completely ignore these impossible values (as I originally suggested) before any filtering step.

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PS. I had to add ".txt" to file to be accepted. Do you have any control over which file types are accepted? Surely a GPX file is a reasonable file to upload, and shouldn't need to resort to silly ".txt" trick to fool the website into uploading. Maybe confusing for other forum users too.

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Well and what you expect Andrew when computed track force you to jump 7 metres :).


Check line 3189 in file (14.25 m) vs next 3192 line (7.5 m).


And attachments - I!m aware of this problem, have to write to developers of this system what to do with it.

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You would have to agree the value of -400% has made the gradient graph totally useless to view. This is not an imported track where an argument could be mounted that all elevations must be accepted, but a track created by BRouter. A value of -400% is about -75 degrees. For a fast cycling profile this is clearly a bogus value. As I already said I'd expect/ hope these values to be ignored prior to the filtering step. Yes I fully understand a 7m step change has caused this bogus value.

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Andrew, I absolutely agree that such value is total nonsense for bike ride. Anyway you cannot expect that Locus should automatically ignore such values. What about cases when such value make a sense and it is expected value?


My practice is, that when I download any track with such crazy values, I then use function "Fill altitude" that for me in all cases fix incorrect altitude values in any track.

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>Anyway you cannot expect that Locus should automatically ignore such values

it could ignore such values in situations where it knows they are nonsense, but not to pursue this impossible dream further because...


...I've never used the "Fill alitude" function before. Thanks a lot for making the suggestion. That's a reasonable compromise. The spike reduced from -400% to -30%, and now I can see Y-axis detail for the gradient.

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Both Locus and Brouter use SRTM3 altitude data based on 90x90m space shuttle radar survey.

Everybody who uses these data should know there are many SRTM artefacts. Some are just data errors, and some of them are corrected. I supose there may be more SRTM3 versions, with different error correction progress. Also, some software may use SRTM data or track altitude filtering.

But some artefacts are related to fact how terrain features affect averaging of 90x90m radar altitude data. Sources of artefacts causing sharp SRTM altitude jumps are mainly:

narrow valleys, rivers, forest passages, urban areas, tunnels, bridges.

That is the reason why Brouter uses 10m altitude hysteresis filter, that is filtering out many, but not all artefacts, as it is a trade-off between filtering and distorting.

Once can have 20-30 m artefact jump in few metres, if you review SRTM altitude profile of a route you are familiar with.

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