I am assuming this track from one of our team is a spike.
Doppler speed (top line) far higher than track point. Not seen one like this before.
Interested in any feedback




Merry Xmas and a speedy New Year

That is really interesting Lao, were the #s significantly higher than the sailor expected? if not how did it even get spotted (and therefore how would otherws know if they were posting the wrong figures?)

No the sailor just cross checked the track point (2nd window) with the result window and asked for a check.
Next best speed was very similar.

I have see just a very few instances of this over the last few years. Luckily it is a really obvious error in the Doppler. I have no explanation of what causes it.

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sailquik said...

I have see just a very few instances of this over the last few years. Luckily it is a really obvious error in the Doppler. I have no explanation of what causes it.

Sailquik, I am not so sure that it is a really obvious error in the doppler in this case. The doppler speeds match his other runs pretty closely and the track shows the run is in the same place as the other top speed runs. I wonder whether the v shaped dip in the track points meant it missed the data for the acceleration and therefore is a few knots short?

The more I look at it I think the doppler was correct but an error in the matching trackpoints.



This shows the previous 2nd fastest run similar profile and same angle off the wind

Hmmmm, you may be right. Can you email me the data and I will study it more closely?

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lao shi said...

I am assuming this track from one of our team is a spike.
Doppler speed (top line) far higher than track point. Not seen one like this before.
Interested in any feedback




Merry Xmas and a speedy New Year

how did you copy that graph was you useing realspeed, my probram doesnt have a copy and paste allso my second graph only goes to speed( Track,lat,long,time and speed), what do i need to do to get the rest up thanks

Keef, I used the snipping tool in windows vista (allows you to capture a section of the screen on your computer) or you can use Alt+ Prnt Scrn keys to capture your whole screen and then paste it into a program like paint or a photo editing program.
The graph comes from Realspeed and comes up automatically (version 1.928, go to http://www.intellimass.com/RealSpeed/Single.htm to get the latest version).
Hope this helps.

Sailquik will send file, thanks.

Ahhhh.... There is a missed data point where that dip in the trackpoint speed is and where it diverges from the Doppler speed. it is 2 seconds between trackpoints instead of one. I think this is the cause of the trackpoint speed diverging and I would say it is indeed the trackpoint speed that is wrong. It looks like the Doppler speed is correct.
It is a pity that the track stopped recording there. It would have been interesting to see if the trackpoints got back on track later.......
In this case, I would say count the Doppler speed. There are 9 sats right through and no change in the HDOP (which in itself is a bit strange).
I will consult with the GPS maths brains when I get a chance to check that they agree and see if they can come up with an explanation of the trackpoint divergance. But it seems clear to me that it is the trackpoints in error, not the Doppler speed. The bit you would count is well after the missed point so you have more than 10 consecutive points over the 10 seconds of interest.

thanks loa shi ill try the upgrade