It has been brought to light recently that the existing system of using trackpoints for alpha calculations on GT-11's, vs doppler for GT-31's is creating a bit of a problem for people who are running both devices.

It seems that the GT-11, which we recommend to use trackpoints for, gives a substantially higher reading compared to the GT-31 (which we recommend to use doppler). This normally gives GT-11 users an advantage of around 0.5 knots -- which can equate to many places in the individual rankings.

In one case, someone was wearing both devices, and got a doppler alpha values within 0.02 of a knot between the GT-11 and GT-31: gpsteamchallenge.com.au/sailor_session/show?date=2009-12-23&team=10 This indicates to me that using doppler on a GT-11 can't be that bad.

As more of us are going towards the GT-31, I'm considering making it a rule that all users (regardless of device) use doppler if available for alphas. This seems to be a fairer system for all. Of course, this depends on the technical committee figuring out if this is viable.

EDIT: Changed text above to make it clearer what the issue is. I think that simpler is better, and if everyone's using doppler then that makes the system fairer, and simpler.


Technical people: What do you think?

Edit 2: Can all people who use a GT-11 and GT-31 at the same time please PM me? We would like to have some more data to compare, this will let us make a sensible decision.

mineral1 said...

Just looked at the GPSTC site, cant see a bloody thing for snow

Virus

mineral1 said...

Just looked at the GPSTC site, cant see a bloody thing for snow

I thought Nebs has dandruff

Merry Xmas everyone

I think as many using the same calculation method as possible is best.
Any change just needs step by step screen shots for us less technical people showing how to set up Realspeed, GPSAR etc. Given that and the possibilty of phoning someone for advice on getting the set up right I hope most will be happy.
p.s. love the snow

Yeh makes it simpler and fairer. A good move

A little bit of background on this:
When the GT-31 first came out the results between the 11 and the 31 were very different for the Alphas. The GT-11 gave more spikes and errors with the Doppler and the GT-31 gave totally nonsensical Trackpoint results. So we had the 11 giving consistent results with Trackpoints and 31 doing the same with Doppler. Easy solution (but not entirely satisfactory by any means) was to go with the current ruling.
Now, revisiting comparisons (brought to our attention by Steve's data) it is obvious that firmware upgrades and tweaks have improved the Alpha results from both to the point where there is very little evidence of the spikes and irregularities seen before.
Preliminary review suggests that we now may have very consistent results between the GPS's using Doppler for both, as long as they have the latest firmware! Even the trackpoint data seems very comparable.
More testing is needed to confirm this in as wide a range of conditions as possible but we need to do it reasonably quickly so we can try to start the new year with whatever seems best.
I think we can arrive at a much more consistent outcome for reasonable comparative purposes. I still have some deep reservations about the accuracy of both the Doppler and the Trackpoint data when used for Alphas but I guess this is moot if we can get consistency. I think we will really need to wait for 5 or 10 hz GPS's to get more accurate results. Hopefully, within the next couple of years............
I have got a firmware update for a prototype GT-35 which has a 5 hz chip in it as well as the 1 hz sirf3 chip so direct comparisons can be done for Doppler. Unfortunately, 5 hz trackpoint data is so 'see saw' that usually the standard software filters discard it, so comparison of 5hz and 1hz trackpoints is no good with this unit.
On the very limited data I have now (one pretty average session lasy week with a best Alpha of just 22 knots) it seems that the Doppler 1 hz data and 5 hz data are very close. Hopefully I will get some more data with GT-11, GT-31 and GT-35 side by side in the next week or so.
If anyone else has both GT-31 and GT-11's (with latest firmware) and can get some side by side data, please send Nebbian and I your tracks. The more data we can get from different people and places, the better.
Please send tracks to me at sailquik (at) hotmail (dot) com

DavMen said...

Track points V's Doppler - really I have no idea which of these my GPS (GT-11) spits out.

I have my GPS set up as recomended on the GPSTC site and use Realspeed to work out my values - Realspeed is also set up to give the values as per intellimass site settings.

My speeds are generally a lot slower than most so I don't see 0.02 of a knot being an issue.

If your going to make it more complicated than that I'll opt out thanks, and go back to B&J.

Don't stress. Your GT-11 saves all the data needed for using either method of calculation. It is then just a matter of having the right setting in Realspeed (in the properties of the Alpha division) to get the desired type of result. This is very easy to check and change like this:

Right click on the Alpha division and select 'Edit'



Then change the calculation method to Doppler by clicking on the white spot.



then click on 'OK' and you are done. Easy!

elmo said...

edit.........

My defunct currency denominations worth

GT?? Doopler
Garmin TP

Should be?:

GT-?? - Doppler
Garmin - Rubbish bin!!! [}:)]

sailquik said...


Preliminary review suggests that we now may have very consistent results between the GPS's using Doppler for both, as long as they have the latest firmware! Even the trackpoint data seems very comparable.

In the Christmas spirit I agree with Daffy on this. The playing field will only become level if everyone uses the same firmware for their GPS units, whether it's the GT-11 or GT-31. If not you will have gained nothing other than enforcing a rule which is still open to manipulation.

At the end of the day the GTC was created to have some fun and encourage people to get out and sail through the unique Aussie concept of mateship and friendly rivalry. It's done this admirably but, as was seen earlier this year when the rules were challenged, it led to the loss of a participant and some bad blood. Bringing in more stringent rules and enforcing them may cause more harm than good. At the end of the day it's a personal thing and best left to trust where the individual posts the times they are happy and confident with. There's no sheep stations involved so lets trust each other to do the right thing.

Merry Chroostmas from the frozen Gorge.

Thanks Sailquik & Decrepit - Checked my settings and all is set to "dopper if available" except for my Alpha GT-11 set to track points.
So long as all I need to do is transpose the fiquires from RS to GPSTC i'm OK.

Merry xmas guys

Its easy to say just do this then do that but there is probably more than one person here who struggles to download the info at times.I have to insert the alpha 500 division every time Realspeed is used.I am also using the original GPS firmware because I KNOW that to try and upgrade means I will have a non functioning GPS.
Does KA72 read out in dopler automatically?I have tried to set Realspeed up to read out alphas but get the message,"No Way D#$&%!^d, go away".[}:)]
Actually the real message is"C:program filesproject 1default.rsp was denied"

Mark has said he will install new firmware for me but I fear he doesn't realise the nightmare that may land on his desk.
Currently the proud owner of 1 functioning GT31 and 2 dead GT11's.Sending them to Taiwan 4 repairs next week.
PS the screen dumps look great sailquick,its a shame I havent got an alpha to edit.

Must stop now before I throw the bloody laptop out the window.[}:)]

decrepit said...


So is the same firmware available for GT11 and Gt31?????
The latest firmware for the GT11 on the Mt Best site is 1115, and I downloaded that 2 years ago.
I'm not game to try and put 31 firmware into the 11, without an assurance that it won't kill my gps.

No, different firmware for GT-11 and GT-31.
Hmmmm... I thought the GT-11 firmware had been updated more recently but I guess 1115 must be the latest. Will look at my GT-11 tonight and see what I have on it.
Updating firmware on the GT-31 is much simpler than it used to be. Just follow the instructions here: http://www.mtbest.net/setting-up-navi-GT31.htm
Likewise, the GT-11 is not too hard. Here are the instructions: www.mtbest.net/setting-up-navi-GT-11.htm

There is usually someone in your GPSTC team or sailing buddies group who can help you do a firmware update if you are not confident the first time. Ask around. :-)

Yes Mathew it worked.......sort off.....But now all i have is trackpoints, I think.
All the divisions are listed now including Alpha 500 but there is no results listed.
It will be fine though. I'll just chuck the laptop back out in the garden where it deserves to be and have a Xmas beer. Sort it out next week

Thank you so much Sailquik for your analysis, the rigor you bring to the challenge is very much appreciated

Thanks also to AUS1111 and Snides for bringing the issue to our attention, without this we would never be able to go forward.

As always, new rules are based on recommendations from the technical committee, and I prefer to keep this discussion open. This way everyone gets to see why we make the decisions we do, and add their input if they feel that something has been missed.

I hope that we can go for doppler in all categories for 2010, it will remove the temptation to use older devices when newer, more accurate ones are available. It will also make the system simpler, and easier for new users to get set up. Simpler is better

So I await the results of Sailquik's experiment with bated breath!

The KA72.com (free reader) site will calculate all Alphas for GT-11 tracks using doppler data for all tracks dated 1 Jan 2010 onwards.

Tracks from before 1 Jan 2010 will continue to be trackpoints indefinitely.

The site can tell whether you have used a GT-11 or GT-31, based on the firmware data that is stored in the output file.

Garmin data files will continue to be processed as trackpoints.

Dylan

Well done Dylan, that was quick work.