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RS400atC View Drop Down
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Posts: 3011 		Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post Topic: Fleet GPS tracking
    Posted: 25 Mar 13 at 5:21pm
Originally posted by MerlinMags

....

I think it will be OK as long as you are interested in position, not speed. coughAlbacorecough. If you want to examine which route was the most profitable up the beat, or see who went straight to the gybe mark instead of arcing wildly off course, the exceptions/errors would be obvious.

Or perhaps they might simply look like an extra wiggle....so you'd have to be prepared to discount lots of other wiggles too.


Yes it will give the big picture, but not a lot else. A lot of dinghy sailing is about quite small distances, a boat width at a mark for instance, or an overlap where one metre is tons.
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Posts: 588 		Post Options Post Options   Quote MerlinMags Quote  Post ReplyReply Direct Link To This Post Posted: 25 Mar 13 at 3:47pm
Originally posted by RS400atC

If it works well 99% of the time, how do you separate the exceptions from when something interesting happened?


I think it will be OK as long as you are interested in position, not speed. coughAlbacorecough. If you want to examine which route was the most profitable up the beat, or see who went straight to the gybe mark instead of arcing wildly off course, the exceptions/errors would be obvious.

Or perhaps they might simply look like an extra wiggle....so you'd have to be prepared to discount lots of other wiggles too.
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Posts: 3011 		Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post Posted: 25 Mar 13 at 3:21pm
Originally posted by alstorer

I think that "10m accuracy" claim is very, very out of date is all.
 
Not for a single position, without information from previous positions.
In fact the consumer gps makers don't claim to be that good.
You can get better accuracy by averaging and procesing, but it involves making assumptions that may not always be valid in a dinghy.
If it works well 99% of the time, how do you separate the exceptions from when some thing interesting happened?
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Posts: 1020 		Post Options Post Options   Quote Oli Quote  Post ReplyReply Direct Link To This Post Posted: 25 Mar 13 at 3:06pm
im currently encouraging others at the club to track their races, helps with our standard courses and mark postions if we need to modify them at all.  also very interesting to watch the replays to give an insight into who is doing what and where to make/lose ground.

i use motionx to record track on iphone in an aqua pack, seems to be accurate enough for what im using it for.  others use speed pucks or garmins.  the motionx has a nice feature if others are also using it to share on a channel that can be watched online live or after the race.
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Posts: 2899 		Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 25 Mar 13 at 2:45pm
I think that "10m accuracy" claim is very, very out of date is all.
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Posts: 588 		Post Options Post Options   Quote MerlinMags Quote  Post ReplyReply Direct Link To This Post Posted: 25 Mar 13 at 2:22pm
I have read that consumer GPS units can only expect accuracy to the nearest 10 metres, yet my smartphone and tablet display my location on a satellite image and manage to pinpoint the correct corner of the house where I'm sitting. Probably because I've been sitting still for the past 10 mins and they've taken an average? May not be accurate when on the move.
 
Some people do find the live displays are fun to watch for a big event, but for me the real value is always in looking at the tracks afterwards, and seeing the top 10 boats versus what the tail of the fleet are doing.
 
For example: I'd love to see how the leader's weaving on the reaches gains speed, and how the numptie's wide arc on the reach loses distance. Sometimes you don't take any action about the things you read in books until you see the proof of it in real life....
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 24 Mar 13 at 10:25pm
It was about £350ish.
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Posts: 3011 		Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post Posted: 24 Mar 13 at 10:05pm
Originally posted by Peaky

I've got a little device that is based on a 9 axis inertial measurement unit, which measures roll, pitch and heading every 1/100th of a second and uses a canny bit of maths to ensure it is accurate. It's about the size and weight of a small matchbox and stores the data on a SD card (and can also stream via Bluetooth to a coach boat). I think it could be very useful as a training aid to measure just how upright you are, what trim you have, how well you roll tack etc. Next task is to link it to a speed puck to be able to assess the effect on speed.


That's more like it!
What do these things cost nowadays roughly?
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 24 Mar 13 at 9:05pm
I've got a little device that is based on a 9 axis inertial measurement unit, which measures roll, pitch and heading every 1/100th of a second and uses a canny bit of maths to ensure it is accurate. It's about the size and weight of a small matchbox and stores the data on a SD card (and can also stream via Bluetooth to a coach boat). I think it could be very useful as a training aid to measure just how upright you are, what trim you have, how well you roll tack etc. Next task is to link it to a speed puck to be able to assess the effect on speed.
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Posts: 3011 		Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post Posted: 24 Mar 13 at 8:11pm
Originally posted by Reuben T

It could be interesting to make some of the top sailors at an event carry them so us mortals can see what they have done differently, bust I suppose this is similar to its training use. I can't see it being used extensively though, too much cost and complication.

And too little real information.
GPS is not that accurate.
To make any sense of it you need wind data, boat heading and acceleration data.
It works better on bigger boats where the GPS errors are smaller in relation to a boat length, and acceleration and pitching, rolling, turning are less.
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