I looked into the GP102 .fit files some more. It turned out to be rather easy with the FIT SDK that can be downloaded from www.thisisant.com/resources/fit. The SDK contains an executable jar file to create text files in .csv format from .fit files (FitCSVTool.jar in the java folder). Here's an example of what the result looks like:
So the files contain latitude and longitude data. They are encoded as 32-bit ints (which is what the "semicircles" means), which gives a granularity of about 1 cm, more than enough. Kind of cool to get the .csv file so easily, lets you play around with the data. For the 001.fit file in the upload I mentioned earlier, the median difference between positional speed and doppler speed is 0.59 km/h. The maximum is 44.2 km/h, which was a spike in the positional data after a crash where the GPS lost reception for about 10 seconds. Doppler speeds during this time were < 1 knot.
pheww; thanks Boardsurf, I just bought 3 canmores so happy to hear they are precise !!! (especially considering I'm starting a freerace challenge locally !!)
Very interesting stuff boardsurfr. Thank you for your work with the Canmore and your excellent insights. As already stated, I agree that the availability of the trackpoint data means that the Doppler speed data from the Canmore can be at least compared. It does make spotting errors much more likely and makes the data from these units far better than the old trackpoint only Garmins etc. and probably on par with the GT-11 in that respect.
The GT-31 does not rely on HDOP to get speed error values. It uses 'SDOP' (Speed Dilution Of Precision) for accuracy monitoring. This is a term coined by Dr. Tom to for convenience and is not a standard industry term AFAIK. In the SIRF literature they refer to this type of calculation as Estimated Horizontal Velocity Error (EHVE).
Data of this type is also available in the UBlox .ubx binary output from their modules, but is not normally available from the SIRF chips unless you get the specific SirfDrive modules and the associated firmware. My understanding is that Locosys used the SIRF SDK to write their own firmware to get the parameters needed for SDOP specifically for the GT-31. Unfortunately, other GPS using the SIRF3 chip do not usually have this capability switched on.
Which brings us back to the Thingsee One. It uses a UBlox GPS that outputs .ubx binary files (at up to 10z) which include speed accuracy data. UBlox GPS have been tested specifically in speed windsurfing situations by a number of people and their abilities are fairly well known. I took part in one test which compared their results with the WSSRC fixed timing at Luderitz with excellent results.
The Canmore GP102+ output has Doppler speeds and more than decent accuracy, despite NOT being a dedicated GPSSS unit.
And, another thing. Considering Doppler speeds from a SIRF Star IV unit. May their accuracy be affected by lack of >1Hz logging frequency and xDOP; and do they depend on firmware?
Reliability is a disputable term. I understand if one wants all datas are OK without need to check, then he needs all that stuff, 10Hz, xDOP, ...; but if one is OK with checking the top results for no spikes, same as it has been so far, maybe he can do without.
0,1 knots accuracy "is still not good enough for meaningful competitions and rankings"? Really? Come on, do you really think one is faster or slower than someone else because of a <0,1 knots difference? Would you lightheartedly hold up a trophy won by resulting 0,05 knots faster than your buddy in #2?
I think when we say "feasible" we mean different things. Maybe you mean "technically" while I mean "economically"?
Apart from the fact that I never wrote "blah blah the canmore is OK for me" anywhere. At least because the Canmore has too small a screen to look at on the beach through a bag, and is not waterproof.
Now if we want to be serious, I think we should try to understand what the other is saying.
I am trying to bring it down to a few concepts in order to see whether "geeks" and "normal users" ("What is a 'normal' sailor? One who is interested in accuracy, not fantasy?", remember?) may be OK with the same kind of units, or if their needs are too much different.
Your statement about speed differences in rankings explains your point of view. What this means is, a speed difference of 0,01 knots between two guys that might have happened to do such speeds in different weather and sailing conditions and in places maybe thousands miles away from each other is something worth to be considered. And even need to know how much 'reliable' such difference is.
I used the term "feasible" a few posts above, as you answered to that I thought you knew that.
There are already a few very simple questions you could quickly and easily answer here if you wished to, should you ever find the enthusiasm. So I am starting to think that it's not the enthusiasm but rather the answer. An answer that fits with the general meaning of what you are saying, at least. Anyhow I understand you completely: if I was going round in circles, I would be done too.
And, I still have lots of fun sailing even when choosing not to use any logger.
Sorry for disturbing.
Thanks for all that have posted. There's been some great discussion and an incredible level of technical understanding shown.
In a nutshell however, as I am one of those guys that "just want's to post some GTS data with his local team mates", I'm thinking that the Canmore GP-102 will be an ideal cost/benefit solution for me. If I can improve on my stats (particularly my Alpha), I'm happy. At this personal stage in my sport, I'm just keen to have a bit of fun and to review my day's efforts over a beer or two...
Thanks again - although would still appreciate any further advice on the subject.
TP
One small thing to remember about accuracy, if we're not worried about it then any comp ( gps3, gpstc) might only have a top 50 and top 100 category etc. Why ???? Cos the margin of error might be that large! It turns any results into a guess of , it could be 1st or 50 th position.
Is this what we want to accept with a cheaper system.
We buy fins, wetsuits for about the same cost as a GPS but some would believe that it's too much..... ?????
In my view the point is not about how expensive or not a proper gps should be, but rather how much meaningful speed differences of <0.1 knots are. Expecially in a sport like our and even more so when comparing speeds done in different days, different conditions and different places.
GeoITA. Where did you get the idea that the accuracy is as good as 0.1kts? Read my previous comment about this again.