A couple of people have asked me whether we're using trackpoints or doppler for the challenge this year.

Personally I'm using doppler as it's less mucking around when you get the file, whereas trackpoints tend to give you a slightly higher reading.

Is GPS-SS using doppler only this year?

What are other people's thoughts on this?

Basicly GPS-SS are saying that is you have a navi gps you should be posting doppler. I think we should stick trackpoints for now and see what happends with
GPS-SS.

hardie said...

<<<<<<<<<<<<<<<<<<<<<
However, I do reiterate, to use 2 separate measurement systems seems ridiculous to me!!

I can see your point hardie, but as the navi gives you the option of giving greater accuracy, I'm now inclined to use it.
Also as Elmo and Nebs says, it saves the hassle of checking each result, to make sure it's not an invalid, then having to do several recalculations when your best times are invalid (that can take a while if you've raked several kms up).

As there are no sheep stations involved I think it should be left to personal choice for the moment. If and when everybody has doppler capability, then we can require everybody to use it, if that's how the majority feel.

There are two main reasons the GPS-SS guys are going over to Doppler. The first is that it is more consistent. This is better for high end competitions and rankings where the results may be only separated by less than 0.1 of a knot. (Trackpoints from Foretrex and Geko in side by side test can, and have varied significantly more than this. The variation between trackpoint speeds for side by side GT-11 is smaller but still significant).
This means that the range of speed from side by side GPS are smaller using Doppler.

The second is that with this smaller range of deviation it is possible to use a system of claimed speed. This is a step towards making GPS speeds more officially acceptable (just one step towards I must emphasize). This means that the error that can be calculated from statistical analysis can be deducted off the speeds so one can say they have done at least the speed claimed with 98% or 99% probability. Note that this has no effect on the rankings of comparable GPS devices and is only aimed at comparing with official speeds. Theoretically, it also allows the same rules to apply to different GPS devices. For example, if you use a Garmin Foretrex or Geko it is possible to deduct an amount off it as well to make a claimed speed 99% probable. The fly in the ointment here is that the deduction for Garmins (and other non Doppler units) is probabaly going to be so high that the users will spit the dummy and go play with model trains or something.
There is a lot of statistical analysis going on at the moment in the background by a highly respected GPS-SS member in Europe to try to refine the claimed speed deductions but there are still a lot of decisions to be made about it and it is unlikely to be implemented completely in GPS-SS for some time.
In the meantime, I suggest we continue to use trackpoints for this year and see how the GPS-SS situation unfolds. Since ours is very much a fun ranking and mainly a team event anyhow, the results are a bit more accurate because they are always an average of two members. (the more samples you use, the less error there is.)

Also it must be noted that even within GT-11 devices the difference between Trackpoint speeds and Doppler speeds can be quite significant. EG, for my session on Thursday it took my 5 x 10 sec speed from 41.7 knots down to 40.9 for Doppler. Other riders reported similar differences. So I would say to those guys posting Doppler results in the Team challenge, take note of how much you are taking a hit on your speeds.
I have found that when using GPS Results and RealSpeed to do the analysis, there is very little difference in the ease of getting results from Doppler or Trackpoint. Most of the time the results need no further adjustment either way if you have a reasonably clean track.

GPS-SS also verifies tracks. Not one track in this challenge has been checked, or at least very few.

Keep it simple, if doppler floats ya boat use it.

mkseven said...

GPS-SS also verifies tracks. Not one track in this challenge has been checked, or at least very few.

Keep it simple, if doppler floats ya boat use it.

yep mine was checked from the 30th dec....i must look dishonest

mkseven said...

GPS-SS also verifies tracks. Not one track in this challenge has been checked, or at least very few.

I check any tracks that look like they might have a mistake in them, or if they are wildly fast. I'm hoping to implement a system where users post the tracks to the site, and anyone can verify them for up to a week after posting, but that's low on the priority list at the moment.

I like the 'instant gratification' element of the challenge -- and as far as I'm concerned users are innocent until proven guilty. Others might not agree with this viewpoint

I've just seen this debate from a different perspective.
So far it's all been about the individual.
But this is a team challenge.

Shouldn't it be the right of the team captain, to ask that trackpoint data be posted, if he/she thinks their team is being unfairly disadvantaged by members posting in doppler. (Especially if said member is the fastest in the team).

The members can always paste the doppler results into the comments section.