Boat Fiducial Markers for Video

[DefectiveDave]

Hey guys,

 

I had an idea recently which I thought I would share in case it was useful to others. I'm sure others have done it, but I didn't see it elsewhere in the forums.

 

Essentially I placed fiducial markers on my boat which can be seen in my video. Since I'm using a wakeye which is pylon centered, I can get an excellent idea of the relative angle of the rope with respect to the path of the boat's travel. Currently I'm only using them to gauge how high up on the boat I am getting during the gate pullout, but they could be used for general spatial reference for a variety of purposes.

 

For now, the fiducials are simply black marks on masking tape which are spaced at 0 ft (where the rope is at 90 degrees from centerline, so maximum width) and then 1 ft, 2 ft, 3 ft, and 4 ft back from 90 degrees along the side of the boat. I also performed some measurements from the pylon and using simple trig know that approximately:

 

0 ft = 90 degrees from centerline

1 ft = 73 degrees "

2 ft = 58 degrees "

3 ft = 44 degrees "

4 ft = 36 degrees (this is the one we see first in the video when pulling out)

 

Here is video from the only day so far where I used the fiducial markers. Forgive the skiing, it was the first time on the water in 2-3 weeks and it wasn't pretty.

 

 

The first 2 passes are 32 and 34 mph at 15-off, 3rd pass is 22-off, and the rest are 28-off. I think it's nice to have those reference points and I can now tell that at 28-off I'm probably somewhere between 50 and 58 degrees up on the boat during pull out. This translates to a gate width of between 36 and 40 ft. For me that means that I'm close to where I want to be on the pull out, but that sometimes I'm not getting all the width I need to get out to the buoyline.

 

However, I was also able to determine using the markers that glide speed may be my bigger problem. A friend who is a significantly better skier than myself had a much stronger gate (body position, speed, everything) at 28-off but with a gate width of only 33-36 ft. This appears to be because he has more speed when he turns in for the gate.

 

So I already feel like I've learned something significant to help my skiing. If you would have asked me before using the markers I would have guessed that I was further up on boat during my gates, but the video doesn't lie. Additionally, I wasn't sure that my turn-in speed for the gate was too low, but having compared gate height and other results from another skier I'm now very convinced that I need more speed at the turn-in no matter how rushed the gate feels (I'll get used to it).

 

Anyway, data is good and this is very cheap and easy. Moving forward, I think I might need a camera with a wider FOV (maybe a gopro) in order to better record the fudicials higher up on the boat and I may need to get a shorty shock tube so that it doesn't block the fudicials. More fudicial markers for higher resolution wouldn't hurt either. I'm at the end of my season this year, but I hope to explore and improve upon this next year.

[dchristman]

@DefectiveDave Since you posted this, you now have a fiduciary responsibility to continue the development of a video system with fiducial markers. B)

[dchristman]

@DefectiveDave Since you posted this, you now have a fiduciary responsibility to continue the development of a video system with fiducial markers. B)

[DefectiveDave]

@dchristman ,

 

I see what you did there, haha.

 

I don't think a video system is in the works here. I believe this is useful for getting some basic information and maybe for qualitative comparative analysis, but I don't expect to be deriving velocity/acceleration curves. :-P

 

While I'm sure that's possible with enough work, I don't think the temporal or spatial resolution would even begin to approach something like RAT-IPA. I will probably just use this method to get approximate measurements at points of interest. Things I've thought of so far:

 

- How high on the boat at gates and buoys

- Angular velocity at centerline (needs some markers on the aft wall)

 

If you have any ideas on how I might be able to get more out of it then I'm all ears. :-)

[DefectiveDave]

@dchristman ,

 

I see what you did there, haha.

 

I don't think a video system is in the works here. I believe this is useful for getting some basic information and maybe for qualitative comparative analysis, but I don't expect to be deriving velocity/acceleration curves. :-P

 

While I'm sure that's possible with enough work, I don't think the temporal or spatial resolution would even begin to approach something like RAT-IPA. I will probably just use this method to get approximate measurements at points of interest. Things I've thought of so far:

 

- How high on the boat at gates and buoys

- Angular velocity at centerline (needs some markers on the aft wall)

 

If you have any ideas on how I might be able to get more out of it then I'm all ears. :-)

[Chef23]

When I skied with Lucky Lowe at his place a couple of years ago he had been working on a set of stickers you could put on the gunnel of the boat to be able to see the width you are getting while skiing. I am not sure he ever did anything with them to bring them to market.

 

[Chef23]

When I skied with Lucky Lowe at his place a couple of years ago he had been working on a set of stickers you could put on the gunnel of the boat to be able to see the width you are getting while skiing. I am not sure he ever did anything with them to bring them to market.

 

[Bruce_Butterfield]

@DefectiveDave, good idea to see where you are. If you are getting 50-58 degrees on your pullout, that means you have 32-40 degrees more to get where you need to be

 

Not trying to be a wise guy, it's just that many skiers hold themselves back by being too narrow at the start.

[Bruce_Butterfield]

@DefectiveDave, good idea to see where you are. If you are getting 50-58 degrees on your pullout, that means you have 32-40 degrees more to get where you need to be

 

Not trying to be a wise guy, it's just that many skiers hold themselves back by being too narrow at the start.

[mwetskier]

for years we placed 2 inch wide green masking tape in 3 locations high up on the passenger side top rail running over the edge and down the boat side for several inches. our purpose is for the skier to work on getting higher up on the boat and maintaining width during the glide. the tape markers offer immediate feedback to the skier and work best for straight boat runs down the lake while the skier is ' free skiing '. its very easy for the skier to see the marks and note his progress to learn what techniques works and what doesn't.

 

in actual coursse skiing its pretty much impossible for the skier to pay any attention to the marks but i suppose a video might pick them up. but since we have never paid any attention to that i suppose we have abandoned our fiducial responsibilities. not that theres any thing wrong with that.

[mwetskier]

for years we placed 2 inch wide green masking tape in 3 locations high up on the passenger side top rail running over the edge and down the boat side for several inches. our purpose is for the skier to work on getting higher up on the boat and maintaining width during the glide. the tape markers offer immediate feedback to the skier and work best for straight boat runs down the lake while the skier is ' free skiing '. its very easy for the skier to see the marks and note his progress to learn what techniques works and what doesn't.

 

in actual coursse skiing its pretty much impossible for the skier to pay any attention to the marks but i suppose a video might pick them up. but since we have never paid any attention to that i suppose we have abandoned our fiducial responsibilities. not that theres any thing wrong with that.

[Garn]

You could use those when you are free skiing. Someone on the boat could watch where the rope goes and tell you if you are skiing to narrow (which is common when free skiing) or if you are wide enough to make the buoys if they were there.

[Garn]

You could use those when you are free skiing. Someone on the boat could watch where the rope goes and tell you if you are skiing to narrow (which is common when free skiing) or if you are wide enough to make the buoys if they were there.

[mwetskier]

@Garn -thats not unlike how blind (disabled) slalom is performed and judged.

[mwetskier]

@Garn -thats not unlike how blind (disabled) slalom is performed and judged.

[DefectiveDave]

@Bruce_Butterfield ,

 

Point taken, more height equals more potential energy and more time to achieve body position before being loaded by the boat (assuming all other things are equal such as turn-in velocity). I definitely have my best gates when I'm widest which is why I need to hold myself accountable, haha.

 

I'd still love to see how high on the boat a big-dawg gets. I don't know that 90 degrees is possible, but if I see someone do it then I couldn't make excuses for myself. At the very least, it would tell me what width at minimum for which to shoot and I'm confident that it's wider than I currently am.

[thager]

Could be wrong here but it seems to me that someone may already have a patent pending on this. Thought it was out of WPB.

[DefectiveDave]

@thager,

 

Are you talking about flag slalom? I remember seeing it on BoS but can't find the thread at the moment. Here is the facebook page:

 

https://www.facebook.com/Flag-Slalom-Water-skiing-without-a-slalom-course-180609865334333/

[thager]

No not Flag. It was a marking system on the boat for slalom skier pullout reference. But, maybe I was dreaming?

[mwetskier]

might be kind o hard to get a patent on visual markings of that nature. i see them all the time on convenience store exits so the camera can record how high you come up on the door -pretty obvious step to apply similar markings to the gunnel to see high you come up on the boat and one of the big requirements of a patent is that it cant be *obvious*.

[DefectiveDave]

I don't think that the idea I've presented is patentable as it is not really novel (it's really just a method of indexing position such as used in stepper motors and a host of other applications) and it is quite obvious if one defines the goal. Anyway, since all I'm doing is suggesting that people could put stickers on their boat and take some basic measurements, I don't have any commercial aspirations. :-)

 

However, that's not to say that someone else isn't trying to patent something similar that does meet patentability criterion. I'd definitely be curious to see what they had in mind.