Waypoint and Courses

by old_man_biking

Downloads: 1,161 (12) • Reviews: 4

Version:

3.0.6010

Updated:

Jun 15, 2016

The elevation correction algorithm in 3.0.4693

The elevation correction algorithm in 3.0.4693

Postby Tisztul_A_Visztula » Wed Jan 30, 2013 3:05 pm

OMB,

what does W&C do exactly in case of a barometric drift in its current version? Does it use pressure data of Weather plugin to compensate or does it still use some DEM data overriding or lets be positive offsetting barometric elevation?

Your website only says

"April 7, 2011:
* NEW: "Add elevation" action: renamed to "Add/fix elevation"; can now fix elevation tracks that come from barometric altimeters which have drifted"

But I found some talks about it eg viewtopic.php?f=3&t=12279&p=68459&hilit=drift#p68459

I mean is the red bolded part of this post from March 2012 quasi the present algorithm in case of barometric drift?

"This IS already implemented - by Waypoints and Courses plugin.
The plugin provides an Add/Fix elevation action which tries to determine the type of elevation error first:
1. "noisy" GPS elevation with
2. drifed barometric elevation

In case 1 the plugin will replace the elevation track by DEM elevation - with all its limitations
In case 2 the plugin will use DEM elevation to remove the drift but maintain the fine resolution of the barometric elevation
The next plugin version will add another compensation: when there's a waypoint near the activity start, it will use its elevation as the start elevation.
This can compensate drifts of the barometric altimeter while the GPS was turned off."


Thanks for the clarification.

Note: I moved this post from GFD to here realizing that that was not the right place evn if I just simply continued a talk there. I hope you appreciate my improving discipline :lol:
Cheers,
Zoltan
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Re: The elevation correction algorithm in 3.0.4693

Postby old_man_biking » Wed Jan 30, 2013 3:44 pm

I just answered a very similar post by dbrillha an hour ago. Have a look there, please.
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Re: The elevation correction algorithm in 3.0.4693

Postby Tisztul_A_Visztula » Wed Jan 30, 2013 4:27 pm

1) Yes, I know. Actually I cut the March 2012 post from that thread. It was some enhancement ideas that you reflected too. I had read it before posting here.

I guess I got 90% of the answer from that thread, but in a bit indirect way, and not in a confirmed direct way. Can you simply confirm with a "yes" that right now none of the weather data are used to identify barometric drift or to modify the elevation data of .fit files by GFD?

2) And I have a second question, not just to you OMB, but to the broader ST3 society.
In the plugin description it is read by OMB: "automatically fix artefacts ("stairs") in the recorded elevation track (a well known bug in some Garmin devices)"

Are you sure that it is a bug? I dont have a long history with my 910XT, but also I could observe that the minimal step in elevation measured by 910XT using its barometer is 2m or so. I simply thought that it is because first our hands move more aggressively up and down than our handlebars or shoulders. While Garmin opted for a step of 0.5m for some handheld and bike devices, maybe they wanted to avoid the fluctuations. The fluctuation can come from the pressure change due to pressing some buttons on 910XT.

So is there anybody around who has 910XT and has tracks without stairs? Or with stairs but with smaller steps? All my activites logged by 910XT are stairs-like.
Cheers,
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Re: The elevation correction algorithm in 3.0.4693

Postby texmurphy » Wed Jan 30, 2013 9:44 pm

Tisztul_A_Visztula wrote:2) And I have a second question, not just to you OMB, but to the broader ST3 society.
In the plugin description it is read by OMB: "automatically fix artefacts ("stairs") in the recorded elevation track (a well known bug in some Garmin devices)"
...

The original barometric "step" in the Edge 305/705/500/800 was about 0.48m. See viewtopic.php?f=43&t=6120
CHnuschti wrote:...there is also a simple explanation. If you look at the ORIGINAL records, you will notice that ALL the elevation gain/losses between the record points are always multiples of 0.48 meters (approx. 1.5 feet). So 0.48 meter obviously is the smallest difference of elevation that can be sensed by the barometric measurement. Considering you usually ride with 20-30km/h (approx. 13-20 mph), your distance per second (of recording) is 5 to 8 meters, so you would have to ride a grade of 6% or more (at this speed!) to reach this elevation step of 0.48m...


However beginning with firmware v3.0 of the Edge 500, Garmin choose to introduce the 2 meter step artifact. This first in the Edge 500 because the 500 has insufficient processor power to handle the extra data screens and IF/TSS/NP which was added in v3.0 for power meter users. Many Edge 500 users choose to revert to v2.8 once the effect on elevation recording was "appreciated". See on Garmin Forums Poor elevation graph since installing 3.0

I reverted quickly from Edge 500 v3.0 to v2.8 because of the elevation 2 meter step bug.
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Re: The elevation correction algorithm in 3.0.4693

Postby old_man_biking » Thu Jan 31, 2013 12:27 am

Garmin FIT Devices plugin has an option to remove those 2m elevation step artifacts when importing.
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Re: The elevation correction algorithm in 3.0.4693

Postby Tisztul_A_Visztula » Thu Jan 31, 2013 7:08 pm

texmurphy wrote:
Tisztul_A_Visztula wrote:2) And I have a second question, not just to you OMB, but to the broader ST3 society.
In the plugin description it is read by OMB: "automatically fix artefacts ("stairs") in the recorded elevation track (a well known bug in some Garmin devices)"
...

The original barometric "step" in the Edge 305/705/500/800 was about 0.48m. See viewtopic.php?f=43&t=6120
CHnuschti wrote:...there is also a simple explanation. If you look at the ORIGINAL records, you will notice that ALL the elevation gain/losses between the record points are always multiples of 0.48 meters (approx. 1.5 feet). So 0.48 meter obviously is the smallest difference of elevation that can be sensed by the barometric measurement. Considering you usually ride with 20-30km/h (approx. 13-20 mph), your distance per second (of recording) is 5 to 8 meters, so you would have to ride a grade of 6% or more (at this speed!) to reach this elevation step of 0.48m...


However beginning with firmware v3.0 of the Edge 500, Garmin choose to introduce the 2 meter step artifact. This first in the Edge 500 because the 500 has insufficient processor power to handle the extra data screens and IF/TSS/NP which was added in v3.0 for power meter users. Many Edge 500 users choose to revert to v2.8 once the effect on elevation recording was "appreciated". See on Garmin Forums Poor elevation graph since installing 3.0

I reverted quickly from Edge 500 v3.0 to v2.8 because of the elevation 2 meter step bug.


Texmurphy, whether do you know 910XT came out to the market with this 2m style or it was just the result of some later firmware release?

I checked the posts of the forum you linked in and I found the same, 910XT can log elevation data with an incremental change of 0.2m, but all the elevation numbers meaning less than 2m difference from the last "stable" elevation data are just short term elevation data.

I think Garmin does not consider this 2m stair issue as a bug, I guess they opted for it to make it easier for themselves to calculate total ascent and descent. It is like carving out the living flesh from a human body to get rid of some wound.

Do you see any chance that they give up this bad habit of them?

My understanding is that GFD plugin can only linearly interpolate data which helps sometime, but sometime it is what hides any eventual steep grade after some full flat. For the time being it is almost impossible to get a good estimation of max grade of an activity. I sold my Magellan Switch Up two days ago, because I had been pleased with the elevation of 910XT, you know I simply overlooked the stair issue not having made enough tests, so maybe it was a mistake to get rid of Magellan.
Cheers,
Zoltan
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Re: The elevation correction algorithm in 3.0.4693

Postby texmurphy » Thu Jan 31, 2013 8:57 pm

Tisztul_A_Visztula wrote:...Texmurphy, whether do you know 910XT came out to the market with this 2m style or it was just the result of some later firmware release?...

I am only familiar with the Edge 500 firmware disaster where Garmin has introduced new bugs in each release as they introduce new feature elements, yet never correcting those issues the 500 community would like to see fixed (Courses, Trackpoint positioning, Stepped elevation, Corrupted activity .fit's, &c.).

old_man_biking wrote:Garmin FIT Devices plugin has an option to remove those 2m elevation step artifacts when importing.

omb, does this mean the more discrete elevation recording is present in the .fit or that you interpolate to avoid stepping?


@omb, when you introduce both bugs and features, the bugs get resolved and the features get improved 8)
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Re: The elevation correction algorithm in 3.0.4693

Postby old_man_biking » Fri Feb 01, 2013 1:40 am

texmurphy wrote:omb, does this mean the more discrete elevation recording is present in the .fit or that you interpolate to avoid stepping?

Yes (the latter).
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Re: The elevation correction algorithm in 3.0.4693

Postby Tisztul_A_Visztula » Fri Feb 01, 2013 9:06 am

old_man_biking wrote:
texmurphy wrote:omb, does this mean the more discrete elevation recording is present in the .fit or that you interpolate to avoid stepping?

Yes (the latter).

Can you also confirm with a "yes" that right now none of the weather data are used EITHER to identify barometric drift OR to modify the elevation data of .fit files by GFD?
Cheers,
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Re: The elevation correction algorithm in 3.0.4693

Postby Tisztul_A_Visztula » Tue Feb 05, 2013 4:42 pm

For the information of 910XT users

I was hunting for some relatively old activity logs on GC and found some with firmware 2.20.

Now my understanding is that Garmin opted for some bigger elevation incremental change as a threshold, I mean bigger than the old 0.48m, but originally (when 910XT was launched) it was not 2m, but 1m or so.

I tried to clarify the issue with some Garmin rep, he always referred to GC and how it displays the elevation data of 910XT, while I insisted on that GC is not important, because the .fit file is the one which stores elevation data this way. He admitted that the engineers do know about it, but this guy said that they do not consider this as a bug, more like a problem of activities of short distance. So they seem to be artists saying that the stairs cannot disturb anybody on a chart of long distance activities.

Nice, isn't it?
Cheers,
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Re: The elevation correction algorithm in 3.0.4693

Postby Tisztul_A_Visztula » Wed Feb 06, 2013 8:01 pm

Tisztul_A_Visztula wrote:1) Yes, I know. Actually I cut the March 2012 post from that thread. It was some enhancement ideas that you reflected too. I had read it before posting here.

I guess I got 90% of the answer from that thread, but in a bit indirect way, and not in a confirmed direct way. Can you simply confirm with a "yes" that right now none of the weather data are used to identify barometric drift or to modify the elevation data of .fit files by GFD?



Closed.
Cheers,
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Re: The elevation correction algorithm in 3.0.4693

Postby Tisztul_A_Visztula » Sun Feb 17, 2013 1:28 pm

texmurphy wrote:
Tisztul_A_Visztula wrote:...Texmurphy, whether do you know 910XT came out to the market with this 2m style or it was just the result of some later firmware release?...

I am only familiar with the Edge 500 firmware disaster where Garmin has introduced new bugs in each release as they introduce new feature elements, yet never correcting those issues the 500 community would like to see fixed (Courses, Trackpoint positioning, Stepped elevation, Corrupted activity .fit's, &c.).


Texmurphy,

have you ever proposed to Garmin to switch back to the good old 0.48m incremental change for Edge 500? There is some page for the ideas, http://www8.garmin.com/contactUs/ideas/, and I as a forever idealist asked it for 910XT.

There should be more people complaining not just to the Support and to the Helpdesk. But also sending the same message to Garmin Ideas. I mean to the thrashbin called Garmin Ideas. :-)
Cheers,
Zoltan
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Re: The elevation correction algorithm in 3.0.4693

Postby texmurphy » Sun Feb 17, 2013 8:15 pm

Zoltan,
You might be interested in the "problems" or maybe they are "feature enhancements", being experienced by the mass-market beta testers (i.e. bike computer purchasers) of the *new* Garmin Edge 810.
The thread Elevation difference between 500 and 810 has a discussion claiming "raw" data is dumped into the 810 .fit data whereas "smoothed" data is put into the 500 .fit data. (I don't believe this).
Other discussion on the 810 forum on various other topics show again that Garmin is willing to have their users do the product development testing.
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Re: The elevation correction algorithm in 3.0.4693

Postby Tisztul_A_Visztula » Mon Feb 18, 2013 1:53 am

Thanks for pointing it out for me.
Cheers,
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