Wednesday, July 6, 2016

Reliability of the calculation of total distances and accumulated heights: original versus optimized tracks

We reproduce here some questions from one user related to the reliability of the calculation of the height and, also, cumulated climb and descent in the case of both the original track and the optimized track. 

Also, we will seize this opportunity to give a brief overview of our error treatment processes.

A summary of the questions of our user:

How reliable is the calculation of the distance and height difference your tracks and traces optimized?

I would like to know the most reliable figure for the distance and the accumulated climb in the case of the attached track.

Also, when I open the link " info points list" on the right side of the table which appears there,  there is an "optimized trace" with a cumulated climb of 537.43m. 

As I understand, your system detects the GPS system's recording errors and also corrects the optimized trace?

So in summary, the result obtained is generated from the corrected trace.

In this case, I note that reliability of the original track is D (= bad) and correction level 3.

And the final result for the distance and cumulated climb: 14.143 km and D + 466 to 469m.

Is this the right answer?

Here is a summary of our responses:

Indeed, 14,143 km and D + 466 to 469m are the figures describing your track

On this screenshot, we can see that for this part of the track...

was recorded with this profile by the GPS device.

That is why our system has applied the corrective algorithms.

One can intuitively see that it is very unlikely that the track’s original data, without the corrections we will write about further in this post, is describing the real profile of the physical path traveled by hikers.

We take the opportunity of this example and your questions to describe our error handling process briefly.

This is a schematic description of the data processing process IBPIndex:

1. Resolution of different problems caused by the GPS recording device in the .gpx track "original" essentially:

• Analysis of abnormal points

• Jumps / Steps in the profile of heights product, for example, of stops on the route or geographical elements that blocked or prevent a proper reception of the GPS signal

• Optimization of the number of points recorded on the track: the more points are recorded, the bigger the accumulated mistake is introduced in the calculations.

• Other error treatments methods...

…and we obtain the optimized track

2. On the optimized track, we apply a series of other correction mechanisms. 

The main one is an automatic correction system working in 8 possible degree levels ranging: from level "0" no correction, no correction only optimization only, up to level "7" maximum correction.

Once the data has been again revised/corrected we assign a reliability degree to the track, according to the following scale:

"A" = Very Good
"B" = Good
"C" = Fair
"D" = Bad
"E" = Very Bad

And after this final set of analysis and corrections, the "Final Track" is obtained.

This "Final Track" is the base on which IBPindex calculates the final statistics of the tracks that you see on our website: positive and negative cumulative altitude difference, percentage rise, etc.

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