Adjusting power data for existing rides

[Jonathan O'Keeffe]

I've been riding all winter with TrainerRoad, which is an app that measures speed on a trainer and converts this into "virtual power" using a known power curve for the trainer.  TrainerRoad spits out a TCX file, and I load this into GC.  All good.

I just got a PowerTap and now have real power data, which of course doesn't correspond exactly to the "virtual power" I've been getting from TrainerRoad (although there is a nice tight mostly-linear relationship between them).  So now I'd like to go back to the existing rides I have in GC and adjust the power figures downward so that they correspond with the real data I'm getting from the PowerTap.

Looking at the data directory in GC, it looks like the ride data is stored in JSON files there, and it would be relative straightforward for me to process all those files and adjust the power figures.  I suspect, however, that there's more to the data repository than just the raw power information in the JSON files, so my question is, will this approach work, or are there other areas I would need to adjust as well?  Or would this be a bad idea that would hopelessly corrupt all my GC data?

An alternate approach would be to adjust the power figures in the original TCX files, and reload them into GC, but I'd prefer to avoid this because I have a bunch of metadata attached to the rides in GC which would be lost if I had to reload everything.

Thanks in advance for any assistance with this.

[Julian]

You might try the "Adjust Torque Values" menu option in the "Tools" menu.  That said, I'm not sure how that will affect the zero-torque values in the original file...  Perhaps someone else knows...?

[Mark Liversedge]

The only real data is in the ride files -- everything else is derived from this.

You should close GC, make your batch changes across the ridefiles and then restart GC.

It will recalculate all the metrics etc from the newly changed raw data.

Cheers,

Mark

[Jonathan O'Keeffe]

Thanks guys.

I also just discovered that you can copy and paste from/to the Edit tab in analysis view, which is incredibly useful.  This makes it very easy to select all the data for a ride, dump it into a spreadsheet, do any manipulation you want, and then just paste it right back into GC.  This is working great for me.

[Malcolm DingleFB]

Hi

I have a similar situation to that described in this topic. I have looked through GC but can't seem to find the feature I am hoping for. A search through this forum turned up this topic which is very similar to the issue I am dealing with - I am hoping, before posting to a wider audience, that someone viewing this topic may be able to guide me. 

I have two power meters - one on my PowerBeam Pro trainer and a Stages Power meter. Obviously the Stages is used outside, but I also use it on my trainer when doing FTP tests. That test gives me an accurate FTP value from both the trainer's power meter as well as my Stages meter. For what ever reason (calibration issues, imbalance of left/right leg etc) the two meters read off from each other by around 5% at FTP power levels (as well as Tempo Z3 and upwards). The approx 5% is within the combined accuracies of both manufacturers so I am not concerned that either meter is "wrong", only that I want to have consistent power data within GC. FTP tests aside, all my indoor rides' data is captured from the trainer's power meter and all outdoor from my Stages. As the discrepancy between the two meters is consistent over a number of FTP tests, I am happy to apply a factor to the trainer's data (P*0.95) before uploading it into GC. 

The process I use is to load the ride into GC from my Garmin, then export it as a CSV file, apply the factor to the Power column in the spreadsheet, save, and reimport the file back into GC (after deleting the initial import with they unadjusted data). It works but is a little laborious given that I must do this for half my rides. 

Q: I was wondering whether there was an easier way. Is there already the ability to apply an adjustment to ALL power values of a given ride in one simple action? The current option to edit a ride seems to only allow editing of a single data point, not to apply a factor to all power values of the ride. Am I missing something that is already there? Or should I turn this into a requested feature? 

thanks

Malcolm 

[Mark Liversedge]

If torque is present you can do this with tools->adjust torque.

It wasn't intended to be used that way .. I wonder if a 'Scale data series...' tool would help - and let you choose a data series and a factor to apply.

Mark

[Malcolm Dingle]

I don't think torque is present in the FIT file I have, or at least its not visible through the Analysis--Edit option of the ride... And as you say, I suspect the "adjust torque" wasn't intended to be use in the way I was describing. 

A "scale data series" tool certainly sounds like what I had in mind. 

I suspect that the situation I have described will become increasingly common as more people have multiple sources of power data (power meters on multiple bikes, trainer with a real power meter or as the original poster had, a trainer with "virtual power"). You don't really want to (and can't in GC) have multiple CP values (one for each meter) and in any case, that wouldn't be desirable even if it were possible. Scaling one power meter's data to match another (after having done some tests comparing the two meters and determining the scale factor) is the best option I suspect. 

If I can figure out how to do it, should I put this as a feature request for future GC versions?

thanks

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[Martin Wifling]

I have the same problem with my Ergomo/SRM/Stages/Daum Mix. All are almoust the same, but different.
A tool which easily adjusts all power data would be a great benefit. At the best directly by uploading a file, say when a profile of each PM is described.

[Derek Clegg]

Old topic I know but adding this link here as its relevant

The fit file tools website has a power adjustment function, note i havent used this yet but intend to use it tonight after i noticed the power from last nights ride is off

https://www.fitfiletools.com/#/top

On Thursday, 14 March 2013 13:04:41 UTC, Jonathan O'Keeffe wrote: