Forums > Windsurfing   Gps and Speed talk

Mandatory use of KA72 with GPSTC

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Created by AJEaster > 9 months ago, 5 Jan 2016
sailquik
VIC, 6068 posts
6 Jan 2016 7:03PM
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vando said..


sailquik said..
I can think of a few reasons why making it widely known might not be a good idea. If the venue is likely to invite controversy from other interested parties like nut case bird watchers for instance, having the evidence online would be not a good idea.

Some places might be OK when used by a very small number of sailors, but the impact might not be predictable if more and more tuned up where access may be controversial or access through private or public land and may be lost to all through complaints.

I think there may also be a view some people take that if they go to a lot of trouble and expense to find a good spot, they should be allowed to reap the rewards with their mates for a while before it becomes too widely known. I don't really have too much of an issue with that as long as they are not silly about about trying to hide it indefinitely.





Your not doing anything illegal are ya daffy .




I am saying nothing........

Ahhh, y'all know me. If I ever find a great spot I can't contain myself. I blab about it to anyone who will listen!

decrepit
WA, 11828 posts
6 Jan 2016 6:22PM
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AUS 808 said..
Boombuster said..
my point is how do we do this as some GPS units put out files that are not readable on for instance realspeed which I have.


Which of the approve units cannot be viewed on Realspeed?
To my knowledge they all work fine.


Realspeed doesn't do .fit files from the canmore and it doesn't like doing alphas from the GW52.

decrepit
WA, 11828 posts
6 Jan 2016 7:49PM
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Ian K said..
>>>

I did a whole lot of experiments walking around an oval with a Garmin and a tin can. I walk at about 4 knots, but once I got the hang of it I could easily get 6-7 knot peaks. The later GPS are probably better, and satellites are logged, but does logging satellites get around this loop hole? It would have had full reception while playing catch up. Do we know what sort of pre processing goes on with later GPS?

Or you can just hitch a ride on a jet ski.


With the windows version of GPSResults, clicking the "SDoP" button will show the level of accuracy on the speedgraph.
Although the number of satellites may not change, the accuracy of the doppler data is compromised when satellites are shaded, this inaccuracy may not be picked up unless you look at the SDoP display.

www.seabreeze.com.au/forums/Windsurfing/Gps/SDoP/

Windxtasy
WA, 4013 posts
7 Jan 2016 8:47AM
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Unfortunately all the processing programs come up with slightly different results for the same file, and with very small differences determining the rankings at the top, it would be ideal if everyone was using the same program to process their data (whether it be KA72 or something else, consistency is desirable).
Obviously some people have their favourite programs and are very resistant to change, so at the very least, people should consistently use the same program and not swap and change to whichever gives the best number on the day.
Regarding keeping tracks hidden and having secret spots, it has been tried before and it did not go down well within the team concerned nor with other teams, and resulted in mass exodus of sailors to other teams and retirement of the captain.
If you need to keep tracks private because you shouldn't be sailing there, then you shouldn't be sailing there...

decrepit
WA, 11828 posts
7 Jan 2016 10:00AM
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My main concern isn't with the different results from different programs, if the data is good the difference is minimal.
My concern is with data that isn't good, that's when the differences start to creep in.
For instance I've just analysed a Canmore file where the device was slipping under the arm, restricting satellite view, KA72 and GPSarPro give similar results for the NM and Alpha PBs, but GPSResults is 2kts less for both of them.
My main concern is that people wear their GPSs so that they don't have a restricted sky view while sailing.
(And on the upper arm, can be a problem for alphas)

Every body posting to KA72 doesn't create a level playing field, it gives an advantage to those not wearing their GPSs appropriately.

AUS 808
WA, 439 posts
7 Jan 2016 6:49PM
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decrepit said..

AUS 808 said..

Boombuster said..
my point is how do we do this as some GPS units put out files that are not readable on for instance realspeed which I have.



Which of the approve units cannot be viewed on Realspeed?
To my knowledge they all work fine.



Realspeed doesn't do .fit files from the canmore and it doesn't like doing alphas from the GW52.


Mike, we run our Canmore files through GPS Visualizer to convert to GPX like we used to do with the Garmin then into Realspeed no problem

sailquik
VIC, 6068 posts
7 Jan 2016 11:46PM
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As I have said before many times, the different programs get the same results with no significant differences if they are set up correctly and if the file is not a dodgy one. There are sometimes files with errors and sometimes those errors are quite large. The different programs sometimes handle those errors differently and come up with a different result, but usually it is fairly obvious there is an error in the stand alone programs. When these errors are discovered and reported, the authors of the various programs work hard to find a solution so they handle then with the same result, usually rejection. Dylan is no exception, but when those errors pop up in KA72, they may not be picked up unless they are quite obvious and/or have been checked in one or more of the other programs. Just because any program gives you a peak speed PB 5 knots higher than you have ever approached before, does not mean it is necessarily true! You could just have discovered yet another way to screw up the program calculations, and in spite of constant troubleshooting and problem solving to try to cover every possible error situation, it amazes me that we are constantly finding more ways to screw up the calculations. Most of the recent issues have involved new GPS units like the 5hz GW-52 or the 10hz Thingsee One that present new challenges for the software designers, GPS units that save limited data like the Canmore, or GPS users that find ever more ways to disrupt or interfere with the GPS signal to their GPS antenna.

In the days before KA72 when everyone had to analyse their own data in a program on their own computer, most users quickly got a feel for what looked right and what didn't. If they were not sure they would usually ask someone else to check it. But still, some errors did get through.

What I am trying to impart here is that you can not always trust computer software to give you a valid result in every conceivable situation. You need to be aware of things that sound a bit too good (or bad) to be true. Its not unlike the kids in math class who punch some numbers into a calculator and come up with a figure they just accept without looking to see if it actually makes sense. (That is one of the big challenges of Math teachers today).

For example, when my good friend, and super fast sailor Jaques had a 50 knot peak speed on one of his two GT-31 GPS's we were all pretty stoked for him. Then we noticed his other GPS only had a high 48 peak. Although we really, really wanted the 50 to be true, further investigation clearly revealed it to be an error. Very disappointing to say the least. If he had only used one GPS, it would have been very much more difficult to spot the error, and even harder to accept the analysis that it was an error.

I could give you dozens of examples, but you have probably seen or heard of a few yourself.

So here is another example. I picked a random file from my recent sessions and ran it in RealSpeed v1.929, GPSAR-Pro v5.4, GPS-Results V6.144 and KA-72 Speed Reader.




Now before someone jumps up and down and tells me 'see, they are different'........

Some of the differences are due to rounding of the third decimal point. Totally insignificant!!

GPSAR-Pro refused to give me an Alpha result. This is because the results from the other programs are of a very unusual Alpha where I actually stopped and set off again. Not really a proper Alpha and one could argue that only GPSAR-Pro got it right in this case. But is also remarkable that all the other programs got exactly the same result from what is clearly a dodgy Alpha. When I have run proper Alphas in various programs with clean files I have always get EXACTLY the same results.

The 1hr Results are slightly different and I can't explain that except to observe that they are two and two. There must be a slightly different parameter in the calc somewhere and it was good I found it here. Yet another like of investigation opens. But again, the difference of 0.18 knots is hardly going to be significant in any competition and would mostly be smaller than the maximum error deviation (SDOP).

The total distances is an interesting one because this is where the program defaults may need to be tweaked by the user.

GPS-Results come with a min speed of 5 knots set as default. The policy of GPS-TC and WGPSSRC is to set it at zero and accept small incidental distances of drifting or walking to the waters edge and back etc. If you have GPS-Results, set it to zero and turn off 'filters' and you should get identical results to RealSpeed.

GPSAR-Pro also allows setting of a min speed. I don't what the default setting is but mine was set to zero. It still got a slightly different result but it was the same as KA72. Yet another line of investigation appears. I will need to check if this is consistent over various files. In any case, the difference of a few tenths of a KM is not significant.

So there you have it. I stress that I just picked on file at random. I didn't run a few and cherry pick one to enhance the comparison as is clearly evident.

I think any reasonable person would agree with me that all the programs give the same results from a clean file.







decrepit
WA, 11828 posts
7 Jan 2016 8:58PM
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AUS 808 said..
decrepit said..

AUS 808 said..

Boombuster said..
my point is how do we do this as some GPS units put out files that are not readable on for instance realspeed which I have.



Which of the approve units cannot be viewed on Realspeed?
To my knowledge they all work fine.



Realspeed doesn't do .fit files from the canmore and it doesn't like doing alphas from the GW52.


Mike, we run our Canmore files through GPS Visualizer to convert to GPX like we used to do with the Garmin then into Realspeed no problem


Hmmm, yes well if you convert the .fit file, realspeed doesn't have a problem with the canmore, I'll grant you that, but at the moment don't try and process GW52 alphas with it. But that may change, a little bird has told me Mal is onto it.

Dylan72
QLD, 632 posts
8 Jan 2016 8:14AM
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AUS 808 said..


decrepit said..


AUS 808 said..


Boombuster said..
my point is how do we do this as some GPS units put out files that are not readable on for instance realspeed which I have.




Which of the approve units cannot be viewed on Realspeed?
To my knowledge they all work fine.




Realspeed doesn't do .fit files from the canmore and it doesn't like doing alphas from the GW52.



Mike, we run our Canmore files through GPS Visualizer to convert to GPX like we used to do with the Garmin then into Realspeed no problem


I wouldn't endorse or recommend this approach at all.

I get many emails from people wanting to know why they get unusual/inconsistent results in their files, and about 50% of the time, it's because they converted them from one format to another before processing them. (So I am writing from a point of considerable personal inconvenience.)

The file produced by the original device is the cleanest, and running files through another piece of software on the way to your analysis software doubles the chances that something will come out wrong. (not to mention that conversion to gpx often gives a false speed bonus.)


sailquik
VIC, 6068 posts
8 Jan 2016 12:07PM
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If you are going to convert speed file into another format, it is best to use GPS-Results or RealSpeed. That way you can be pretty confident the full precision of the file will be saved. It used to be that you could use the unregistered versions if those programs for conversions but I don't know if this is still the case with GPS-Results.

GPS-Results seems to do a pretty good job of converting .fit files to .gpx without loss of precision, but I will test a few that I have and double check

GPS-Babel should be good as well but I have not had reason to use it for quite some time so not sure.



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Forums > Windsurfing   Gps and Speed talk


"Mandatory use of KA72 with GPSTC" started by AJEaster