Select to expand quoteK888 said..
The Sony spikes are somewhat different in nature to what I've seen on the u-blox. They tend to be short-lived, followed by another period without logging which is a little different to the u-blox thing where the speed is locked and the position changes are uniform.
The u-blox artifacts you describe are what happens at the start of a crash, when the GPS looses reception. Those can sometimes be a problem because the error estimates can increase quite slowly. But u-blox data also can have artifacts more similar to the ones you describe when regaining reception - here's an example:
The first positional speed is very wrong since the estimated position is off, which is corrected in the next point when sats increase from 3 to 5. The 76 knot doppler speed for the first point is also quite wrong, but easily caught with three different filters (acceleration, sats, and accuracy estimate). With 2 boom mounted loggers, such artifacts are quite common when taking breaks in a session, so that one of the units is submerged for a little while.Select to expand quoteK888 said..
As an aside, I'm 99% sure that COROS aren't logging the number of satellites correctly. It looks to me like they are logging the number of visible GPS satellites (not even all of the GNSS constellations) from GSV instead of the number of active satellites from GSA. I've got lots of tracks that include an obvious loss of signal (followed by a spike) but the satellite numbers never drop during that period. The number of satellites being reported never exceeds what is possible from GPS alone, which is one of the things that leads me to say what I did about GSA. Whatever is being logged, it is misleading to say the least.
That does not exactly install confidence in COROS. BTW, have you ever been able to get speed error estimates out of COROS fit files? The GPS3 web site still says it should be present, but then, they are also selling Coros watches.
Select to expand quoteboardsurfr said..
The u-blox artifacts you describe are what happens at the start of a crash, when the GPS looses reception. Those can sometimes be a problem because the error estimates can increase quite slowly. But u-blox data also can have artifacts more similar to the ones you describe when regaining reception ... but easily caught with three different filters (acceleration, sats, and accuracy estimate). With 2 boom mounted loggers, such artifacts are quite common when taking breaks in a session, so that one of the units is submerged for a little while.
What you describe is consistent with what I have seen when analysing all of the data collected from Weymouth Speed Week. The re-acquisition errors are typically when people are inside the main building throughout the day, but there were a couple of instances on the water. Of course, these anomalies don't impact the competition results because they are not on the course and also excluded by the standard filters. I have also seen the GT-31 exhibit spikes after signal re-acquisition on rare occasions, which I found by searching the entire history of WSW data. I have a collection of spikes from various devices with summary charts on GitHub - logiqx.github.io/gps-spikes/
If looking at the WSW data, bear in mind that some riders drive to a launch spot, hence some legitimate 50+ knot speeds. I identified the actual spikes using a variety of standard filters, combined with some geo-fencing.Select to expand quoteboardsurfr said..
That does not exactly install confidence in COROS. BTW, have you ever been able to get speed error estimates out of COROS fit files? The GPS3 web site still says it should be present, but then, they are also selling Coros watches.
Accuracy estimates aren't present in the FIT files produced by COROS. The extras in their FIT exports are sats, HDOP and COG. I located "confidential" documentation for the Sony chipset on GitHub and it only produces the standard NMEA outputs, no hAcc or sAcc metrics. As an aside, hAcc can potentially be a useful proxy for sAcc when chipsets produce positional accuracy estimates, but not speed estimates. The correlations are pretty easy to see in the summary charts in my "gps-spikes" repo.
With regards COROS in general, I've documented the issues that I am aware of on GitHub. I don't know what (if anything) has been done within their dev team, other than internal discussions and reviews of the list. I think it is safe to say that attention to detail is not their forte - github.com/Logiqx/gp3s-coros/issues
In other news, I've just ordered myself a FR 255 to accompany my APEX 2 Pro and Motion Mini. I'm looking forward to seeing my last NM, best hour and alpha results whilst on the water, thanks to GPSTC v4. Doing some track analysis will also be a secondary "fun" bonus.
Select to expand quoteK888 said..
In other news, I've just ordered myself a FR 255 to accompany my APEX 2 Pro and Motion Mini. I'm looking forward to seeing my last NM, best hour and alpha results whilst on the water, thanks to GPSTC v4. Doing some track analysis will also be a secondary "fun" bonus.
That's good news 
- the more data we get from the 255 from different locations and people, the better.
The GPSTC, would also like comparative files from the 255 and a ublox device. The more data we have the better.
Please send them to info@gpsteamchallenge.com.au
I put the data files for the tests Nina and I have done, with some short explanations and a few screen shots, onto Github at github.com/prichterich/Garmin255/
This includes the first session that was based on the "SUP" activity, which is not suited for speedsurfing. Subsequent sessions were based on "Other" or "biking", which both seem to work.
To look at the data in GPS Speedreader, I suggest to use the "Erase filtered speeds" function from the "Tracks" menu, since the ESP loggers had some artifact speeds when the GPS units where under water during breaks. These artifacts are easily filtered out and thus do not affect the speed results, but they mess up the scaling of the speed displays.
We probably won't be adding much to this in the near future, but if anyone else wants to add data to the repository, either send me the files, or become a collaborator on this project on Github so you can upload files directly (not quite sure how this works but that should be easy to find out).
Select to expand quoteboardsurfr said..
This includes the first session that was based on the "SUP" activity, which is not suited for speedsurfing. Subsequent sessions were based on "Other" or "biking", which both seem to work.
I have a Forerunner 235 which works quite well, but will upgrade to 255 based on your feed back. Using the Garmin Connect site you can choose "Windsurfing" under Activity type, have you tried that?
I don't have the watch myself and never used Garmin connect (my wife just gives me the files). My understanding is that what you choose on the Garmin Connect site is just a description after the session. If that is correct, that it would not affect how the data is filtered at all, since the filtering is done during the session. So you have to make sure to select the correct activity before recording a session. Both "Other" and "Biking" seem to work well, but anything that includes are movement (like SUP, walking, and running) will be heavily filtered to smooth out the arm movements.
Select to expand quoteboardsurfr said..
I don't have the watch myself and never used Garmin connect (my wife just gives me the files). My understanding is that what you choose on the Garmin Connect site is just a description after the session. If that is correct, that it would not affect how the data is filtered at all, since the filtering is done during the session. So you have to make sure to select the correct activity before recording a session. Both "Other" and "Biking" seem to work well, but anything that includes are movement (like SUP, walking, and running) will be heavily filtered to smooth out the arm movements.
That is probably correct. I do get a warning that changing activity type might remove some data fields, but that does not necessarily imply any changes in data, I assume. You could easily doublecheck this by getting your wife to download a file, change the type to Windsurfing, then download another file and check that the files are identical.
I have been using a Garmin Instinct 2S Surf Edition www.garmin.com/en-AU/p/741454 for the past 8 months and selected it because it has a dedicated windsurfing mode and is rated 10 ATM so better suited for high speed watersports like windsurfing.
I wouldn't risk it with an expensive watch that is only rated 5 ATM. It might only work for 2 sessions, or maybe 200 if you're lucky...
Don't expect much from the tide and Surfline features btw as it needs manual (!!!) syncing with your phone which is annoying to do. It also doesn't show tide information of your current location, even when connected to a phone. You'll have to add a location first and manually switch to it which is so annoying that I just don't use it.
Anyway, it has Multi-GNSS support (not the same as multi-band??) and by default it has GPS + GLONASS enabled for the windsurfing activity so I was wondering if anyone has tested its accuracy? I'm not a speed surfer but would still be interested to find out how accurate it is as this might be a suitable watch for some of you as well given its 10 ATM ratng and the dedicated windsurf activity which shows the number of runs on the watch face natively which is quite nice. I'd hope Garmin optimised the accuracy settings for this activity but not too confident.
It also has a SpeedPro option that enables "advanced speed metrics" in windsurfing mode whatever that means. I've just enabled it so can review after the next session.
Is there a way to figure it out without having a second GPS device to test with? I haven't downloaded the raw tracks from the device yet.
I have owned several Garmin 5 ATM rated watches for windsurfing over around 10 years. None have had any issue over many sessions. The only reason I have gotten new ones is for new features. They all still work perfectly. I have not heard of any time a garmin watch has failed due to water ingress, but I am sure it has happened... but is very low risk.
Select to expand quoteptsf1111 said..
Anyway, it has Multi-GNSS support (not the same as multi-band??)
Correct, not the same. "Multi-GNSS" has been the standard for at least 10 years now, even in $50 phones. Using just 2 GNSS systems (GPS + GLONASS) is really the bare minimum, and will tend to produce less accurate data than 3+ systems.
Multi-band uses two different frequency signals from the same satellite. This enables the GPS to better detect problems, for example signals distorted by reflection from the water instead of coming "direct line" from the satellite, since the two signals will give different results. When properly implemented, this seems to give very accurate data (but note that some GPS chips seem to be much better at this than others - even some older Garmin watches with multi-band do not perform that well).Select to expand quoteptsf1111 said..
Is there a way to figure it out without having a second GPS device to test with? I haven't downloaded the raw tracks from the device yet.
You can catch the most obvious problems by comparing the "top speed" or (better) 2 second top speed with the 5x10 average. If the difference is more than 2-3 knots, there's a good chance that the top speed is due to an artifact. Works best when you use a program like GPS Speedreader or GPSResults and also take a closer look at the tracks. I've seen watch tracks with 40+ knot "top speeds" where the entire rest of the track (and the 5x10) showed speeds around 30 knots.
You won't be able to catch smaller errors, where the speed is just overstated by a knot or so, this way. Smaller errors tend to be more common. But if you're not in a competition, they don't matter much.
Thanks for explaining, that's really helpful! I've not hit the 30 knots yet although getting closer (28+ knots in very choppy water on freewave/freeride gear so...). I'm not really chasing that either.
I don't feel that the 2S Surf is particularly sensitive to such problems as the top speed is generally identical or very close to the 2s speed that it records (e.g. 0.1 knot difference). I think that might also be the reason why I've not hit the 30 knots yet as I would need to sail at that speed for 2 seconds at least.
Anyway, I don't have a problem with that necessarily and will use one of the suggested programs to analyse recent tracks later.
Select to expand quoteptsf1111 said..
I don't feel that the 2S Surf is particularly sensitive to such problems as the top speed is generally identical or very close to the 2s speed that it records (e.g. 0.1 knot difference). I think that might also be the reason why I've not hit the 30 knots yet as I would need to sail at that speed for 2 seconds at least.
Watches generally only record speeds once per second, so the difference between top speed and 2 second is small. Also, almost every GPS will show very similar speeds to the most accurate GPS units most of the time. The problem is that they sometimes overstate speed. I know several cases where windsurfers were extremely disappointed after seeing great speeds on the water, but later learning that those speeds were not real. So if you have a new top speed, just take it with a grain of salt, and wait until you checked the tracks at home before getting excited .
To catch those times where the GPS inflates speeds, some GPS chips give speed error estimates, which can be very useful to identify spikes (and longer bad regions, which some GPS chips also produce when loosing satellite signal). It seems that proper use of multi-band signals can basically accomplish the same thing, although there's need for more data to verify this.
The 255 seems to be able to run custom apps. At least it's listed for this app that the author of the app mentioned on Facebook recently (Wingfoiling group):apps.garmin.com/en-US/apps/53e2dad4-250c-4487-b459-e9ea9bb257dd
This also seems popular:
apps.garmin.com/apps/9d47be43-2724-44e4-8f5e-3005b0766087
My Locosys is getting old (I see cracks in the band and I can see it's taking in water and the battery capacity has gotten a lot worse), so I may well be buying a Forerunner 255 soon. Has anyone these apps on it?
A few windsurfers use my App (well actually it is a Datafield).
apps.garmin.com/apps/f0f3fbd5-9de3-4d69-b89b-10b76d6a9f0f
Select to expand quotetbwonder said..
A few windsurfers use my App (well actually it is a Datafield).
apps.garmin.com/apps/f0f3fbd5-9de3-4d69-b89b-10b76d6a9f0f
A few?? If you're not using it then you're a nobody. Written by a windsurfer for windsurfing. Bloody no brainer
Select to expand quotetbwonder said..
A few windsurfers use my App (well actually it is a Datafield).
apps.garmin.com/apps/f0f3fbd5-9de3-4d69-b89b-10b76d6a9f0f
Would it be hard to add 255s compatibility? The screen is smaller, but it's otherwise the same as the 255 as far as I know. I bought the 255s because I found a good deal on it.
Sorry as I stated last year, I have no intention of supporting the 255s watch.
The screen resolution is 218 pixels. Which would mean redrawing some of the screens and creating a whole new set of fonts.
Select to expand quotededekam said..boardsurfr said..
I don't have the watch myself and never used Garmin connect (my wife just gives me the files). My understanding is that what you choose on the Garmin Connect site is just a description after the session. If that is correct, that it would not affect how the data is filtered at all, since the filtering is done during the session. So you have to make sure to select the correct activity before recording a session. Both "Other" and "Biking" seem to work well, but anything that includes are movement (like SUP, walking, and running) will be heavily filtered to smooth out the arm movements.
That is probably correct. I do get a warning that changing activity type might remove some data fields, but that does not necessarily imply any changes in data, I assume. You could easily doublecheck this by getting your wife to download a file, change the type to Windsurfing, then download another file and check that the files are identical.
I can confirm that changing the activity type within Garmin Connect is both safe and useful. Changing the activity type only changes the summary statistics for the activity and not the underlying data. A binary comparison of the FIT exports (both before and after changing the activity type) shows they are identical.
I'm yet to write up my own evaluation of the 255 because shortly after buying the watch, I was busy competing and timekeeping at Prince of Speed. Since returning back to the UK, I've not had a chance to do a proper write up of the FR 255. What I can say is that after about a dozen sessions (windsurf and windfoil), I have been pretty impressed by the quality of the data coming out of the 255.
Whilst testing the FR 255 against my Motion Mini and APEX 2 Pro, I recently discovered a nasty present from COROS in their latest firmware release(s). My write up of the COROS issue includes some comparisons with the FR 255 and Motion, so it might be interesting to readers of this thread. It can be found at logiqx.github.io/gps-details/devices/coros/smoothing/
Select to expand quoteK888 said..dedekam said..boardsurfr said..
I don't have the watch myself and never used Garmin connect (my wife just gives me the files). My understanding is that what you choose on the Garmin Connect site is just a description after the session. If that is correct, that it would not affect how the data is filtered at all, since the filtering is done during the session. So you have to make sure to select the correct activity before recording a session. Both "Other" and "Biking" seem to work well, but anything that includes are movement (like SUP, walking, and running) will be heavily filtered to smooth out the arm movements.
That is probably correct. I do get a warning that changing activity type might remove some data fields, but that does not necessarily imply any changes in data, I assume. You could easily doublecheck this by getting your wife to download a file, change the type to Windsurfing, then download another file and check that the files are identical.
I can confirm that changing the activity type within Garmin Connect is both safe and useful. Changing the activity type only changes the summary statistics for the activity and not the underlying data. A binary comparison of the FIT exports (both before and after changing the activity type) shows they are identical.
Good to know. I actually ordered a FR 255 yesterday, will be interesting to see how it compares to my trusty old FR 235.
