No, better things to do. You can sort out the Garmin accuracy if you want. Yes it does pass as discussed in numerous other topics on this. Just do the work.

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kato said..
No, better things to do. You can sort out the Garmin accuracy if you want. Yes it does pass as discussed in numerous other topics on this. Just do the work.

Yep as I thought. The proof probably involved comparing a Garmin to a approved device and assuming the approved device was right and the Garmin wrong. The approved device was probably not calibrated in any way and is assumed correct because it has extra data sources so it must be.

I'm not saying the approved device was wrong. Just that all are inaccurate to a different degree. Pros like you who make a living on the accuracy of such things prioritise accuracy. Some recreational sailors prefer the simple life with a device that is easy to use and does more than one thing well.

Congratulations on derailing yet another interesting topic.

I'd be glad to answer anyone's *genuine* question about this.

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JulienLe said..
Congratulations on derailing yet another interesting topic.

I'd be glad to answer anyone's *genuine* question about this.

Early stages at the moment but I now have a Gamin 735 with TB Wonder apps and bloody happy with it! And the Motion logger from Julien which I am bloody happy with as well!

I'm not tech minded at all and struggle with this stuff but geez I'm happy to learn! Updates, downloads, where to wear it etc etc!

Using both while sailing and actually happy like that.

Thanks Andrew and Thanks Julien both doing a great job!

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sailquik said..

vosadrian said..
......Life is simple and this is more important to me than some perceived idea that I will be getting inaccurate data which I have seen no evidence of except occasionally when it was obvious and could easily be removed.

Fine it is your choice to use whatever you want, and what suits your purpose, except of course, in the GPSTC competition.

But, the statement quoted above is totally incorrect. It is not "..some perceived idea (you) will be getting inaccurate data..".

It is proven scientific FACT.

But, I agree, it is probably fine for your 'fun' use if you are happy to take the results with a large grain of salt.

My simple mind would think all the devices were tested on a set course (2 marks) and measuring time? If anyone can go straight (maybe not on water!!) and what would the accuracy of the measuring devices be (distance and time) . Dont think it works for the 2s Vmax thingo though.

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Rob11 said..
My simple mind would think all the devices were tested on a set course (2 marks) and measuring time? If anyone can go straight (maybe not on water!!) and what would the accuracy of the measuring devices be (distance and time) . Dont think it works for the 2s Vmax thingo though.

Yes that is over simplifying it.
We know that units that use doppler for calculating speed and have good reception from satellites, that are in an ideal geometric relation ship, will give accuracy that is good enough for our purposes.
Where the problems come in, is when there aren't enough sats giving a nice clean signal, in a good geometric relationship. Units that are able to use multi GNNS systems are more likely to have enough good sats. Units with a better antenna, will also have a better chance of good sat reception.
So in good conditions, with the GPSs having an unobstructed sat view, different units will give very similar results, using doppler.

It's what happens when conditions aren't ideal that is the worry, that's why we place so much importance on accuracy data.

Here's an example of mine from last month.




The GW60 is the red line, my logger is in blue, (my logger is similar accuracy to Julien's, but nowhere near as sophisticated)

The GW60 gave me a top 2s of 33.205kts, my logger only gave me 31.98 a difference around 1.2kts. I of course was a bit disappointed, so investigated why.
For the top 2s, my logger has an accuracy of +/- 0.14, the GW60 only +/- approx 1.3kts, (the bottom red and blue lines). My logger is using 20 sats, the watch is using 7 sats, which should be enough, but I use an underhand grip on this tack, so the watch doesn't have as good a sky view. So it's obvious which unit is the most accurate, and which 2s I should post.

So I'm sorry Kato, unless a unit outputs accuracy data, no matter how much testing is done. I very much doubt it will be approved for GPSTC use.

If anyone is actually interested in some of the science behind the current approved devices for GPSTC, they may find the following PDF written by Tom Chalko interesting.
bioresonant.com/dl/dl.htm?name=SDOP.pdf
For me this was a pretty good explanation as to why certain devices are approved and others are not

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Rob11 said..

tested on a set course (2 marks) and measuring time

Difference between Motion and Luderitz official timing on the best 2019 run is 0.02kn for example.

Every competition has its rules and means for trials. Some do A/B testing, some do multiples testing, some delegate validation to official timekeepers. A repeatability test between identical devices is simple/cheap/fast and will void plenty.

Accuracy, repeatability are dictated by design decisions : how much space/volume you have, how much power you can gift to the receiver, how expensive things can be, how many small improvements make sense, etc. Different choices for different goals.

My first day using the Motion and Garmin what a fantastic combination, used my phone to down my files so easy and simple. A big thanks to Julien for the motion and Andrew for the x2 data fields on the Garmin, very happy.

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decrepit said..
We know that units that use ....

You've lost me as soon as you said "we know that..." the next statement will be "trust me..." Cant argue with these scientific statements

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Rob11 said..

decrepit said..
We know that units that use ....

You've lost me as soon as you said "we know that..." the next statement will be "trust me..." Cant argue with these scientific statements

It's not claimed to be a "scientific" statement, it's observational from experience, and no I don't expect anybody to "trust" me. I'm getting old and stupid and make mistakes all the time. I was just trying to explain, that you can't just take a unit and do a time and distance study to verify it's accuracy. The random factors that produce errors are external to the unit itself. It's how the units report these random factors that matter.

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decrepit said..

Rob11 said..

decrepit said..
We know that units that use ....

You've lost me as soon as you said "we know that..." the next statement will be "trust me..." Cant argue with these scientific statements

It's not claimed to be a "scientific" statement, it's observational from experience, and no I don't expect anybody to "trust" me. I'm getting old and stupid and make mistakes all the time. I was just trying to explain, that you can't just take a unit and do a time and distance study to verify it's accuracy. The random factors that produce errors are external to the unit itself. It's how the units report these random factors that matter.

You got one thing right, you are getting old. But the rest is just wrong

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sailquik said..

It is proven scientific FACT.

Some of you claim otherwise on the scientific statements. I think they may need to learn what makes a scientific fact.

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vosadrian said..
>>>. I think they may need to learn what makes a scientific fact.

OK so define "scientific fact".
I think the term is grossly over used, and almost meaningless.
I guess E=MC>2 is a fairly well proven scientific fact.
But scientists are still looking to find flaws in general relativity. If they do, all those "facts" could get turned on their heads.

Newton's apples created a scientific fact about gravity for a while. We were taught that weight and mass were two separate things, only to find we'd been misled when we moved up a year.

There are "facts" and "scientific facts", what's the difference?
"There are no whole numbers between 1 and 2", is an undeniable fact, but is that scientific? Or just mathmatical

Scientic 'facts' are those things that can be demonstrated and/or proven with a high degree of confidence and repeatability through the Scientific Method.
We rely on them every day for the operation of innumerable devices and systems in our technological world. Scentic 'facts' can be as mundane as the daily timing of sunrise. A GNSS device could not be built without reliance on a large number of scientific 'facts'.

But yes, our understanding of what science tells us is not static or absolute. As our knowledge becomes deeper, our understanding can change.

That said, the Level of accuracy, repeatability, and the degree and frequency of error assiciated with GNSS systems is quite mature and well described.

Consider this: Pretty much every GPS device will tell you a very accurate speed (within a very small margin like 0.1 knots) some of the time. The better ones will tell you that small margin of error more of the time. When the error is larger than is reasonable to fairly seperate sailors of very close skills in a competition, or even in a 'fun' ranking, obviously one needs to be able to know that so the erroneous results can be rejected. How do we know when the errors are too large to be reliable and usable? By having validating data of course.

There are many things that can be done during the design and engineering of a device that can greatly improve its consitent speed measurfing accuracy, and Julien has done those things. Examples: Large, high gain antenna with a well designed ground plane, I very high quality GPS chipset that allows tuning of the parameters to suit the purpose (Doppler Speed). Using Muti GNSS which allows limiting use of satellites to only those with a strong signal, etc. The point is, that if you are designing a device specifically for speed accuracy it will probably be very different from another device that is designed for a different purpose with different priorities.

The way a sailor uses/wears his device can also have a big influence on the quality of the results he gets. It is well documented that wearing any GPS device on the wrist, watch style, can greatly compromise it's performance. A device worn on the top of the head will give expodentially better performance results. The upper arm facing upwards is by far the best compromise for most practical purposes for most people.

We recently saw an example of a guy who posted a 5 x 10 of 23 knots. Most of his other catagories were consistent with that average. But he posted a 2 second peak of 49 knots and thought it was wonderful! You would think that the extremely high likelyhood of this being an error (it certainly was!) would be quite obvious to many people. (He eventually realised and deleted it). But there are also many example of errors in the 1-3 knots range where the sailors initially didn't think to (or perhaps want to) question it. By far the largest number I have seen are from watches and other devices that don't produce any validation data, and in which it is also highly likely they use positional data 'disguised' as Doppler data. No one has been able to prove to me yet that the Garmin Watches actually use the Doppler velocity calculation method to produce their speed data. There is evidence to suggest that they do not. The flaws inherent on getting accurate speed from positional data are well known. And yes, the question has been asked of Garmin directly a number of times with no response.

Scientific fact: you guys answering queries have way more patience then me.

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mikey100 said..
Scientific fact: you guys answering queries have way more patience then me.

No I think we just like the sound of our own keyboard

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decrepit said..
No I think we just like the sound of our own keyboard

So was your claimed "scientific fact" actually a scientific fact?

I drive up the road 1000 times without having a crash. Is it a scientific fact I will not crash when I drive up the road?

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vosadrian said..
So was your claimed "scientific fact" actually a scientific fact?

I drive up the road 1000 times without having a crash. Is it a scientific fact I will not crash when I drive up the road?

Nope that's just "dumb luck"

The following is a link to an interesting post on GPSTC from yesterday.

gpsteamchallenge.com.au/sailor_session/show?date=2020-06-09&team=1

Moz posted the following results in GPSTC


And in the comments section copied the following results from his Garmin watch


The Garmin results are significantly different (greater than 1 kt) across all disciplines. I would not have thought the difference in results would be so large. I've asked Moz
- if they are from the same session
- what GPS device he used to post on GPSTC
- is the difference between this device and the Garmin typical across multiple sessions

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John340 said..
The following is a link to an interesting post on GPSTC from yesterday.

gpsteamchallenge.com.au/sailor_session/show?date=2020-06-09&team=1

Moz posted the following results in GPSTC
And in the comments section copied the following results from his Garmin watch

The Garmin results are significantly different (greater than 1 kt) across all disciplines. I would not have thought the difference in results would be so large. I've asked Moz
- if they are from the same session
- what GPS device he used to post on GPSTC
- is the difference between this device and the Garmin typical across multiple sessions

There's also a big difference in distance
Run the tracks through a different program & compare.

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vosadrian said..

Anyway, this thread was for Garmin use as a secondary... non GPSTC device. It is perfect for that... especially for those already using a garmin for other uses.

Was

I pressed some buttons accidently and the Garmin stopped, i started it again somehow. But to put it straight im trying to learn how to use it still, give me 1 to 2 years. I used the motion logger to post to Gpstc.

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AusMoz said..
I pressed some buttons accidently and the Garmin stopped, i started it again somehow. But to put it straight im trying to learn how to use it still, give me 1 to 2 years. I used the motion logger to post to Gpstc.

Thanks Moz.

Empirical results are illuminating.

I think it would be useful information if you and other sailors, who use both the Motion logger and Garmin watch, continue to provide a comparison between the results from the Motion and the Garmin.

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vosadrian said..
So was your claimed "scientific fact" actually a scientific fact?

I drive up the road 1000 times without having a crash. Is it a scientific fact I will not crash when I drive up the road?

Are you a 'Flat Eather' and 'antivaxer' too?

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AusMoz said..
I pressed some buttons accidently and the Garmin stopped, i started it again somehow. But to put it straight im trying to learn how to use it still, give me 1 to 2 years. I used the motion logger to post to Gpstc.

I had a look at that motion track and it is not what I expected to see. The satellite count is never as high as I am normally seeing, and it drops to 4 a large number of times. The only similar results I have seen were when i had the Logger on my pocket and it had a compromised sky view. Can you tell us how/where you were wearing the logger Moz?

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AusMoz said..
I pressed some buttons accidently and the Garmin stopped, i started it again somehow. But to put it straight im trying to learn how to use it still, give me 1 to 2 years. I used the motion logger to post to Gpstc.

Use the screen lock, no accidental button bumps.

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sailquik said..

AusMoz said..
I pressed some buttons accidently and the Garmin stopped, i started it again somehow. But to put it straight im trying to learn how to use it still, give me 1 to 2 years. I used the motion logger to post to Gpstc.

I had a look at that motion track and it is not what I expected to see. The satellite count is never as high as I am normally seeing, and it drops to 4 a large number of times. The only similar results I have seen were when i had the Logger on my pocket and it had a compromised sky view. Can you tell us how/where you were wearing the logger Moz?

Front of my NP buoyancy vest in plastic container

This has a big impact on sensitivity. It's waterproof, you don't need the box. The top part should be aiming at the sky. Your body might be shielding 1/2 of the sats available. The vest staying wet isn't helping either. (Just compared your log versus my test log which was good.)

I'll reply to all my emails now.