If you click on "info on other devices" in Rules page of GPSTC it takes you to
www.gps-speedsurfing.com/default.aspx?mnu=item&item=gpsother
They have a Certification process for new devices as well as different requirements for devices for average surf session.
This link is in the GPSTC current rule page and is in Bold and does not state ignore the bold link below.
They actually have an approval process documented for new devices.
There are many GPS products in the market that are superior to the current approved list.
They may not supply the end user with SDOP and error data but are no way low grade GPS.
If the link is not relevant then remove it from the rules.
Below is a University study which shows a good accuracy for what you refer to a low grade GPS.
https://www.researchgate.net/publication/266150506_Measuring_the_Accuracy_and_Precision_of_the_Garmin_GPS_positioning_in_Forested_Areas_A_Case_Study_in_Taxiarchis_-Vrastama_University_Forest
"They may not supply the end user with SDOP and error data but are no way low grade GPS."
There's your answer
GPS Doppler speed measurement. Simplified explanation:
Doppler shift is the perceived difference in frequency of radio waves when you are moving towards the source or away from the source.
It can be best illustrated by using the example of sound waves. When a mototbike (or aeroplane etc) is moving towards you you percieve a higher frquency sound pitch than when it is moving away from you. You percieve this difference as a change of pitch when it passes you.
The same applies to radio waves. If you have two satellites, one directly in front of you, and one directly behind you and you are stationary in relation to those satellites (and for arguments sake lets assume they are stationary in relation to you - which is actually never the case) your GPS would measure the frequency of both radio signals and see them as exactly the same (assuming they are the same transmitted frequency). It would then report that you are not moving. If you start to move towards one and away from the other, the one you are moving towards would now be percieved to have a higher frequency, and the one you are moving away from would have a correspondingly lower frequency. From this difference the GPS computer can calculate your speed very accurately.
In practice, the satellites are not stationary, but their exact speed and trajectory are accurately known from constant observation and precision measurement. This data is sent from the satellite to the GPS device constantly, and mathematics are used to calculate your speed.
Of course, it is very rare that a satellite would be either directly in front of, or behind you as you move, so the computer has to take that into account as well. To get a more accurate calculation, the GPS will use multiple satellites at all different angles and resolve both your actual ground speed and also your heading from that data.
One of the most important factors in the calculation of the Doppler speed error data is the orientation (or constellation) of the satellites used in relation to the direction of your travel. The measurements are inherently more accurate if more satellites being tracked are more in front of you or behind you. (the Dopper shift is larger, and therefore the measurements can be more accurate). If more of the satellites are at close to right angles from your direction of travel, the Doppler shift is smaller and this makes accuracy lower. Satellites that there closer to directly above you will also lead to lower accuracy, and those very close to the horizon will lead to lower accuracy also, in this case because of possible atmospheric distortions (most GPS engines have a 'mask' to eliminate the use of satellites lower than about 20 degrees above the horizon). Ideally, for highest accuracy, you want to be using more satellites between around 30 to 40 degrees above the horizon, and more in front and behind your direction of travel.
This is why it is so important for accuracy (both positional and Doppler speed) to have access to as many satellites as possible by using Multiple GNSS (Eg, GPS and GLONASS). In this case there will invariably be more satellites in a more advantageous position for accuracy, and more data for the computer to use to resolve your speed more accurately.
Hope this helps.
Not sure which thread to post in as there is a few on the go right now about the same sort of thing.
Without the error data there is no way to disprove a number claimed. There is a post from a while ago in our team that just simply isn't correct but there is no way to confirm otherwise. Decrepit has been over the numbers and we all know the 2 sec is a spike BUT WE CAN'T CONFIRM THIS due to lack of error data.
I'm sorry Callan to bring this up again (as it's been discussed before) and it was his first ever post with a Canmore given to him by another team member.
This is the session: gpsteamchallenge.com.au/sailor_session/show?date=2018-02-21&team=6
So we can all want the perfect device to do what we want but it simply doesn't exist. There are compromises with what we have and the Canmore is a perfect example of why the SDoP is very important and has to exist on our data gathered to prove the number accuracy as best we can with the tools supplied. Anything otherwise is has no relevance. Sad but fact no matter how many hours of comparison have been logged with a Garmin it still only takes one spike to change everything.
Anyway back to discussing things I don't understand about GPS and data
Cheers
Marty
Thanks for you question Jr1
Please refer to this answer from a previous recent thread for your answer:
3. I am quite comfortable that the current rules are completely compatible with the philosophy of inclusiveness in the GPS-TC.
There is no requirement to officially post your numbers in the rankings. As said, it is more than acceptable to post your numbers (edit: from non approved devices) in the comments for all to see, and to share in the fun. You may be correct that a very few sailors may find even the simplest GPS and computer technology daunting, but I know there are lots of team members who are quite happy to help out with analysis and posting in those situations, which creates yet another oppurtunity for fellowship.
This would be so easy to keep everyone happy. There is currently a selection when you enter the data where you can select positional or doppler. This could be added to or changed so that you can select SDOP or no SDOP (even leave is the same, but re define doppler to mean having SDOP and positional to mean not having SDOP). This particular parameter is redundant anyway of people are only permitted to use a Locosys which has doppler by definition.
Then I suggest the following based on that data. Firstly, this is my preference:
* If someone without SDOP posts suspicious data (or even good data that is in the upper echelon of performance so threatening other sailor results) and the data is questioned by anyone (captain or another team member or from another team), the data is removed and the poster of the data has no right of appeal. Simply they cannot prove the data is accurate so it is removed. Move the burden of proof to the sailor to prove their data is good rather than the other way around.
* If nobody has reason to question the data (it makes sense when compared to other parameters like 2S vs 5X10 and is within the realms of the sailors ability and the conditions), it is allowed to stand and contribute to team results.
This is is another option if above is unacceptable:
* People can post without SDOP, but changes are made to the inner workings of the GPSTC so that data without SDOP cannot contribute to team or individual result rankings. The data is in the users database but has not other effect on anyone else. It appears in the session results and other team members can comment and encourage. The benefit of this option above posting in the comments is that the user can still keep their own PB lists including kms sailed, and all PBs for their own benefit, but it does not effect anyone else. If the user finds themselves getting good results and the team encourages them to put up real data that can contribute to team results, they may then be encouraged to fork out the $$$ on an approved device so they can contribute.
Both of the above options will cause no issue for competitive sailors who are concerned about other sailors/teams getting a competitive advantage due to bad data. In one option the data does not count ever. In the other, data can be flagged and removed if it is causing a competitive issue.
The benefits of both options are that they are INCLUSIVE which is what the GPSTC claim is their philosophy. These changes will attract new sailors who are currently interested but not wanting to buy another expensive device, and the inclusion may encourage them to buy the correct device later because they enjoy it. This will also allow existing members who are not competitive and do not wish to buy an approved device that they do not like to continue to be included without rocking the boat of those who are competitive. I just can't see a negative to this approach other than a small amount of work to implement it.
Glyn did send me Callan's .fit file.
Yes it was a terrible mess, but the 33kts occurred just before a big crash. Without being there to see what happened, there's no way of knowing if he hooked into a big gust then crashed. It was really up to Callan and Glyn to decide, whether to post it or not, well that was my opinion at the time.
Here's a zoomed in look at the 33kt 2s
I've turned filters off, so the 2s gaps get filled in, but that doesn't change anything else.
It doesn't look like a spike to me, a smooth acceleration up to 33kts then a crash.
As said there's no way of being absolutely sure.
The canmore may have been damaged, but Canmores have a reputation for missing data, and if it was worn so it didn't have a good sky view tracks like this are possible with a normally functioning unit. And normally water damage would just kill the unit entirely, not produce erroneous results.
So if the 2s should have been removed you can blame me.
Hi all
I don't mean to burst the strange bubble that you seem to be living in, The response above is a great example of what is going on and why there is such interest in the posts on the forum about gpstc. To say that people can post in the comments is almost laughable as aside from the team competition side of the site most people also use it to track their own progress,Pb and overall distance. If you are only able to post in the comments this is clearly and example of being inclusive building relationships and all of the best things about gpstc.(ha Ha)
I and many others, if you read all of the posts relating to this topic believe there is a clear desire for more people to be involved. Obviously by the reading the response from sailquick the response is quite simply that there is not going to be any changes made and it you don't like we'll that's ok find something else because we are happy in our little world that we have created.
Perhaps people will take the hint and just find something else and that would be a sad day as there is a great community hidden in there somewhere and I have had some great experiences met some awsome people. I wouldn't be the sailor that I am today without the encouragement and comradeship that has been built by being part of a team.
Thanks for posting the images. This is a great example of where accuracy data would help. There are several indications that this may be an artifact, but it is absolutely not clear. It may well have been a huge gust with the sailor holding on for his dear life until he crashed violently. The 33.5 knots a full 3 seconds before the crash point that way. On the other hand, this could have been the GPS going into "dead reckoning" mode when it lost reception, which can lead to artifacts that look exactly like this. With accuracy data, that would have been easy to recognize - the error estimates keep going up gradually in such a situation. In a good run, they remain low until the crash.
Thanks Cocky2 for reminding me of Callan's file.
This is a good example of why the canmore was a mistake, as Peter says, if that file had SDoP, there'd be much less uncertainty.
It's also a good example of the benefits of wearing more than one GPS, if he'd had two canmores on, there'd also be much less uncertainty.