Garmin GPSTC Datafield - to complement the Motion Simple Logger

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segler said..
Timing circuitry has gotten extremely accurate while remaining really cheap. Positional accuracy is the problem. If speed is calculated from positional data, it is noisy. Max speeds are usually unrealistically too high.

Doppler speeds use the timing circuits, not the positional calculations, and are typically much more accurate. K888 states that doppler speed calculations even typically include kalman filtering.

K888 has also stated, from his studies, that pretty much all modern GPS chipsets measure speeds with doppler, but many (or most) of them record the speeds from positional data. To me this is crazy.

K888 examined a FIT file I sent him from my Timex Ironman GPS watch. He saw that my FIT file contained speed data taken from doppler, and recorded as such in the file. The Timex Connect app shows the max speed from these data, but Strava ignores speed numbers in my FIT file and calculates max speed from positional data; this max speed is always 10-20% higher and is not even realiistic.

I sent Strava an email asking them to change their programming to use speed numbers if the upload file already contains them.

GoldenCheetah does indeed use the speed numbers in the FIT file. I don't know about other apps.

You can read K888's stuff here:

logiqx.github.io/gps-guides/
logiqx.github.io/gps-guides/sessions/contacts/marr/

So basically, the speed accuracy from positional data would improve at the same rate as positional accuracy improves (since time is very accurate). So it is desirable in a non-doppler recording device to have better positional accuracy if you want better speed accuracy.

I'm not surprised Strava would not care about the speed accuracy. Strava is basically about getting the best time on a defined path or segment (that you stay within say 20m of that path) between a start POSITION and finish POSITION. They don't care what the speed reading is at any time along the path. They often list an average speed for the "segment", but that speed has nothing to do with the speed the device recorded. It is simply the calculated distance of the segment divide by the time for the segment. Strava is fantastic for cycling and running. I use it for my windsurfing also, but it is not ideal for that since it does not give the windsurfing stats. But they do accept my device.

I have occasionaly had segment match issues because of positional error. Often when I am riding through gorges with poor GPS signal (steep hills on both sides). This is because my path wanders outside the allowed distance from the segment. It can be annoying when this happens if you put in a big effort trying to get a PR.

The Instinct watches are generally a lower level specification (and price) than other Garmin watches. Garmin has made the decision to not support any aftermarket datafields on this series of watches. So they have no internal memory allocated to datafields, I think you may be able to download different watch faces, but that is all.

I have added GPSTC V4 support for the latest Garmin Watches, the 255 and 955
There are a few things to watch out for. regarding the 255 variants
The 255 comes in 4 versions. (255, 255s, 255 Music and 255s Music)
For some reason Garmin have chosen to use an old screen with only 218 pixels for the 2 "s" versions of the watch. I do not intend to support these 2 models. The other 2 (255 and 255 music) are supported. There is no need to buy the music version of the 255 (as was required with the 245) the base model is just fine.

Table of all supported watches for GPSTC V4 (Version 4.25)

I have created an exact copy of my "GPSTC V4" datafield called "GPSTC V4 (Foil)".
This allows you to install both datafields on your watch in two separate Activities.
Then you can set the user settings in one for speed sailing sessions and in the other for foiling sessions.

My settings are

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BSN101 said..
Garmin has a sale on now. I missed out on 245 but got a 745 half price. Will be having a sesh in 2 days. Woohoo

JBHI sale now. Half price Garmin 245 Music

Just joined back into the Garmin club with a Fenix 6 Pro $575 .Now let's see if I can navigate the tech stuff to get it to work. At least the post is a bit slow and it will give me some research time before it gets here.

I have had several requests to add the Venu Version 2 watches to the list of supported devices for GPSTC V4.
I have added:
Venu 2 and Venu 2 Plus (Note the Venu 2S is not supported)
As usual this code has only been tested on the simulator not on an actual watch.
Latest Version is V4.26 (foil version also updated)

See the latest updated instructions at www.haigh.id.au/GPSTC.htm

AusMoz, TheGarmin 735XT does not support the GPSTC V4 datafields, you can of course use the earlier datafields. The above instructions go through the process for installing the datafield within a user created Activity.

Hi. Has anyone else noticed that the results when downloaded onto the Garmin app, has all been rounded to a whole number. I'm using the Garmin Fenix 5. Is there a fix for this? Tia.

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tbwonder said..
Yes I had noticed this. Not sure when it changed. Looking back at some early posts in this forum, I can see screen shots of the phone app and PC app and they both displayed one decimal place.

Now the phone Connect app shows no decimals places and the same Activity in Garmin Connect on your PC shows 3 decimal places.
So it is not the download process, but the display process in the different apps. I use Windows and iphones, it would be interesting to hear what other users are seeing in the Apple Mac world and android phone world.
I don't think there is much I can do to change this, except possibly to add an option to multiply the results by 10.

Ok thanks. Btw I was using this app side by side with my GW52 yesterday, dinging and found the 2s on the Fenix was 2knts higher then the gw52. I was surprised by this difference. Great app btw??

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K888 said..

flatchat said..

Ok thanks. Btw I was using this app side by side with my GW52 yesterday, dinging and found the 2s on the Fenix was 2knts higher then the gw52. I was surprised by this difference. Great app btw??

It's not uncommon for some Garmin devices to produce 2s results which are 1 or 2 knots higher than the GT31, GW-52, GW-60 or Motion.

I've seen this when doing device comparisons so it'll be the watch itself, rather than the data fields.

Here is just one example session - logiqx.github.io/gps-guides/sessions/contacts/kisg/

yes. I've experienced this first hand from the example above. But this one didn't give me any confidence in the F5. About a month ago, my F5 reported a 28knt 2s whilst out dingin. I didn't claim it and wouldn't have expected to reach 20knts in those gnarly conditions. I did dream for awhile though

Someone else may have a better way, but open the activity on Garmin Connect on a pc, download the file using "Export to GPX" under settings, then go to KA72 and upload it, file should be in your downloads folder

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berowne said..
Rigth on Dezza.
You can even do it on your phone at the beach!

I don't believe it is possible to export data files from the Garmin Connect phone app.

Hi guys
I think next time a deal comes up in AU on a garmin watch that works well with tbwonder's datafield I might grab one
Please post here next time anyone sees a discounted deal on a suitable garmin watch
open to budget 200-$500
thanks
Rod

My garmin Fenix 5 has been a great addition I especially like the Hr 0ty & alpha data fields.
I havent used my watch since Oct 30 2022 when every thing was working great. 2nd Jan 2023 & Hr 0ty & Alpha all did not display, all results 0. only plug the watch into my computer to charge & I cant remember if it has done any "auto" updates. I think it must have as it now reports all up to date & sync OK. Any Ideas why 0 results for Alpha 0ty & Hour?

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tbwonder said..
Which version are you using. There is a version number on the launch screen.

V2 10th March 21