Doc .. I had a similar thought from a recent hearing with publicly available (YouTube broadcasted) drone footage of the incident.  I had a new judge on the panel so I followed the normal script .. but had we put that video up front .. as evidence presented by the PC .. things would have gone a lot quicker I think. 

We were prepared as a PC for the new judge to swap sides and present the video if neither party did.  In the end, one party eventually presented it, so no need for that step. 

PS: meaning above that if the entire panel was experienced judges, I may have suggested presenting the video up front. 

It is a long time since I was in this game, but i can recall us considering reopening a hearing at a J70 Worlds based on the claim that the previous day's video recap told a different story. When we looked at the video we were happy to see that we got a complex situation correct. If there is suspicion of error a PC should do something about it, by whatever means available. I am sceptical of electronics accuracy, but in the event of grossly different stories a gps-based system, errors and all, may allow the correct choice.

Doc, I agree, and we recently learned something about RaceSense that I think is worth adding to this discussion. After a recent hearing, I was asked to review a proposed reopening regarding the interpretation of the RaceSense replay. That led me to Doug Wake, RaceSense Director at Vakaros, with some deliberately open-ended technical questions about exactly what we are looking at on the screen.

One important thing we learned is that the animated boats are more than icons following GPS tracks. Their orientation is based on the device's magnetic heading, and the animation uses the geometry of the particular class, including hull shape, bow offset, and orientation. That's important because heading and course over ground are not the same thing. The GPS track tells us where the boat traveled; the magnetic heading tells us where the boat was pointing. Doug specifically cautioned against rotating a boat to make it tangent to its GPS track because that substitutes COG for the measured heading. Vakaros also told us that the displayed orientation should normally be relied upon unless there is an obvious reason to suspect magnetic interference or a calibration problem, which might show up as a boat apparently traveling sideways.

So I'm very much with you on making RaceSense evidence readily available to the parties and protest committee. But I think there's a second piece: we need to teach judges what the RaceSense data actually represents before we start treating the replay like instant replay in football. Otherwise, very precise data can still be interpreted incorrectly. I've put together a short technical guidance paper based on Doug's answers and have asked both Vakaros and the GYA Race Management Committee to review it before I circulate it more broadly.

This technology could absolutely help us get to your "15-minute protest" more often, but only if the people sitting around the table understand what they're looking at.

Would suggest that there are two stages to each protest determination.  First, to establish the facts, to determine what actually happened.  Typically, this is done by each side stating their memories of what occurred.  Second, applying the Racing Rules of Sailing to the facts as accepted by the committee.

Vakaros RaceSense, or another GPS based track, of one or both boats movements, provides a substantial portion of the information needed to determine what happened.  Does not help with hails and other communications.   

Can't see any downside to using the data from Vakaros RaceSense, or another GPS based track, whenever available.   Similarly, for GoPro footage or video recorded.

What are the reasons for excluding such sources?

Note: John D. Farris said above "we need to teach judges what the RaceSense data actually represents".  Agreed.  

My experience from a recent event where one skipper was able to produce the tracking information for his boat and the other sailor either didn't want to produce it or didn't have the skills. This was a simple RRS 10 where Starboard claimed an extreme alteration in course and Port offered that they had kept clear. We reviewed the tracking data but felt it didn't add anything to the facts. RRS 63.4(b). I would use caution when considering tracking information as I have seen first hand where 2 boats look like they collided where in fact it was a close crossing situation.

Doc brings up a good point. Should we change our hearing procedure at events that use Vakaros (or similar)? I think yes. 

The question is at which point of the hearing should the evidence from the device be introduced? Should the PC ask after the validity portion: 'do you have the Vacaros track available and ready to present' at this point?
Could it replace the evidence presented verbally (and boat models) by both parties, therefore eliminating the “you tell what you saw” from both parties? Maybe. 
Have both boats tracks reviewed first and then, if any portion(s) of it is not to the satisfaction of the PC, have the parties add any ‘clarifying details’ by allowing each to ask questions of each other and include witnesses (cannot exclude them) and the PC as well. 

Some of it will then make it longer than desired, but if it is not clear, you are going into a longer hearing anyway.

Benefit: if the tracks give enough evidence to produce FF, then you have the15 minute hearing and dinner.

This will require additional equipment in the hearing room. TV with Internet access would be good to have; connecting video cables, etc. The OA will need to start thinking about this kind of evidence and provide the equipment. To have 5 Judges surrounding a 5” Apple/Android screen is hardly a proper way to judge evidence to produce FF. And we all do it, at times. (Different topic: should the Judges refuse to review an incident on less than the 12 “ screen, per Judges Manual?)

Experience with Vakaros. At relatively recent Westen Hemi and Asia Champs and Nationals, the Vakaros evidence was helpful in two instances and made the hearings relatively short.

At a pre-World Champs regatta, a boat during a hearing dismissed the PC’s request to see the track with: ‘it only an orange line going thru the bay’ and never produced it. The PC had an experienced Judge on the panel that was familiar with the app and it could have expedited the hearing. 

Regarding Vakaros .. there are a few items to stick in your cap. 

Our Annapolis J105 Fleet, in conjunction with Annapolis YC and Eastport YC, have adopted the RaceSense system.  Along with that the other major J105 fleet in SanFran did so as well. 

As was said, the compasses are very sensitive to being taken "out of whack" (technical term).  So much so that, before each day of racing, they recommend calibrating the compass each time (which I do).  This is divergent from what most people are familiar with where you calibrate your boat's compass once and your done.  If this calibration isn't done correctly, the boat's orientation will be off on the plots.  It will appear as if it is sailing cocked/sideways. 

Also, yes the RS/Vakaros system has the outlines of many boats, but the representation of those boat outlines will be reliant on the display tool used.  Many people/companies are developing their own viewing platforms.  One of my fleet members built his own.  So when viewing the data, be sure you understand what viewer is being used and how the boat outline is represented and scaled. 

PS: In other words .. always remember that what you are viewing is someone's representation of data-streams of 1's and 0's.  The choices made by the viewer-designer will affect what you are seeing. 

Velocitek published a study of the Vakaros equipment showing a 1+ meter inaccuracy.  Velocitek's point was that without a fixed base station on land that the RC sensors uses to triangulate and correct for drift and timing that this was not a solvable issue because, physics.  If Velocitek is correct 1+ meter is not an insubstantial error.

If technology exists then we should use it!  It's not going away.

However, we should fully understand/educate users and build it in properly to our process. (Doc's question...John Ferris' guide.)

A simple example of understanding is the accuracy/confidence level.  1-meter accuracy (95% confidence) means the distance between the 2 units may be 1.4 meters wrong.  For Optimists this is more than half a boat length.   The tracking software might say the boats are 2 meters apart, but mathematically, the actual gap could be anywhere from 0.6 meters to 3.4 meters.   

This is not accurate enough for some rules scenarios.

(I have an example of a protest where the tracker (normal GPS) did not show the Optimist tacked and the protestee used that as a basis of a very compelling defence.  However, Jury had a video which clearly did show the tack, and was able to make the correct decision.  Had the jury relied on the tracker, the decision would have been wrong.)

Perhaps WS should be publishing guidance / limitations of use of digital evidence.  Put it in the judges manual perhaps.  With a list of tested systems even.

(See the PDF as an example.)

In answer to Doc's question then... 

As for the hearing process, RRS 63.4(b) allows the protest committee to take 'any other evidence it considers necessary'.  This opens the door to evidence not supplied by the parties. In which case, I don't see anything wrong with PC having access to tracker data - so long as they understand the limitations of them.  e.g. If the tracker is not on the white-list, then accuracy must be presumed to be X. 

The interjection at that early point might save a whole load of questions and witnesses and thus time.

I am verry worried about the comments here.
I have always expected the parties to bring evidence to me. They have to bring the means of watching it. 
I have faught ahains those who said the rc may have a video or recording and i should obtain it. 
I am too busy with my responsability to all competitors, and save if i saw the incident feel the parties should provide their own evidence 
We can give more time to prepare if they request it. 
Yes i am a lawyer, we give decisions on the evidence presented, we do not find it. 
I have no problem at a vacaros event (a minority of events, where because ot the cost the owners do have resources and are used to collating information) saying (by notice not at the hearing) how they may obtain information. 
Perfect information shortens hearings. 
Seeking information helps one party and takes precious time. 
No we should wait for the information to be brought to us. 
As to the screen, yes if we have one the problem with events is the escalating costs. You are advocating increasing the cost base and pricing a jury out of events and clubs. 
We are appointed to finf facts from the evidence presented using our experience and we should stick to this and excell. 

Michael, are you talking in general, to me or to someone else?

Just to clarify...

I started with... " If technology exists then we should use it!"

At an event where good tracker data is being used by RC, it doesn't take much to make it usable in hearings.  Especially these days.

I totally agree.   The RRS predominantly places the burden on the parties to bring their evidence and means to 'present' it. (Appendix M8.a).  I fully support that.  We are not there to build the parties' cases.  Go get it yourself.

 
Well, the RRS has always included the provision that the PC may use 'any other evidence it considers necessary'.  This sets the sailing protest apart from a court system where the process is based only on what the parties bring.   Rightly and deliberately so.  In court the judge just listens.  Courts have people paid to do that job for a living.  Sailors on the other hand are just laymen trying to get a fair result in a sailing race.  Let's do what we can to get that fair result. We are not a court.

So again my point is, if the PC has access to the central 'tracking system' being used and it would improve the quality of the hearings, I absolutely see no problem with them utilising that somehow.  I am not suggesting placing any 'burden' in the rules on the PC to have to use any kind of evidence, if they do not think it necessary.  I'm not suggesting every club has to now go out and buy Vakaros, smart TVs etc., and judges have to pour over tracker replays before every hearing.

But I'm also finding the notion of 'only use technology if its brought to the hearing by the party' (even when the system is being used by race management) a little archaic.  It's there and not going away. It could improve the quality of the decision and save time.  Use it.  Many systems already can be configured so competitors can access the tracks.  Great.  If that's the case, let them find the correct file and take the screenshots etc...

I think it comes down to the confidence and technical capabilities of the PC members, whether to use technology.  I'm sure over time those the software will improve, as will the general skills of judges - making it a no brainer to incorporate the technology into hearings in future.

(As for who supplies the video screen, well if the PC wants to watch a tracker, it should have something to play it on!)

I am curious at some events which 'limit' the use of the tracking system for hearing.

I never really understood this - remember thinking it was rather regressive.  Hopefully, that is becoming redundant now that technology has moved on.

Hope that helps.

No this is a general principle for me.
At big weekly events we may have 50 hearings with arbitrations first. 
We are usually 5 and are fully stretched, nearto if not missing dinner, and editing text later in our accomodation. 
We have enough to do, do but burden the committee with checking valcaros. 
If the parties want it they can call it, we accept all evidence, and decide on its relevance. 

I may be arcahic being british, the parties can bring any evidence they want. 

I do not have time before hearings to review vacaros to see who it may help. 

Yes we may sak for other evidence, this is a good point, we give our own testamony, we ask for pictures of damage,  and with difficult redress ask other boats. 

Just like it being a self policing sport so we rarelly protest, i think the parties are responsible for the evidence they wish to bring. 

We exclude nothing. 

I increasingly get competitors who just arrive and say why do you not have the pc vidio or recording. The world is getting lazy and trying to pass the buck onto the jury. 

I just see this emphasis as, deempowring  competitors, and asking a busy jury to do too much. 

No one is perfect especially when just using the phone.

The tec is really moving forward as previous trackers were not accurate. 

I think by the next olympics the systems will be reliable, and you never know world sailing may issue a guidance outside their inner circle. 

Video etc from coaches has not generally helped me with hearings. The only video i found really helpfull and conclusive was one taken off the rail by a crew on a tablet.
A windward mark was to be taken to port and two boats approached on the port tack. 
The leeward and larger boat started to luff in preparation for tacking. 
The hearing allegation was this boat tacked to starboard forcing the port boat about in an unsamanlike manner this breaking rrs 15.
The video showed that whilst the bigger leeward boat was luffing, the smaller boat tacked and completed her tack to starboard before the bigger boat passed head to wind. 
After the video the protest was withdrawn. 

I have had problems recently with after weekend events, competitors have viewed the event facebook posts, see class rule breaches and lodged hearing requests. They failed. One after flagging the issue was not lodged for 5 hours and was too late, the other the boat was not notified at all except for the hearing request. 
So events may not be finished when you think? 
Go for the new protection on results. Cannot recall the rule number, but it has to be in the si. 

Interesting discussion about the use of tracking data in hearings. I have done a number of events (>10) where Vakaros is being used. The number of hearings that the tracking data has been presented in the hearing is very low (maybe 1 or 2). Only once, did a boat ask after the hearing if we looked at the tracking data. My reply was no, and if we (judges) were going to look at it, the parties would in the room at the time. 

Another example of "odd" Vakaros position records ..

Look at this race.  Watch the tacks just after 18:19:45 for USA 159 (me - Crescendo) and USA 96 (my friend Peter Bowe - Good Trade).  Obviously not accurate portrayals of what our boats did through the water. 

So, without diving into the data streams themselves .. I can't tell you why I'm it's displaying like that.  Is it that the data had gaps and the viewing software filled in the gaps trying to smooth the playback?  Is that what the data actually represented?

We've been talking about accuracy a bit here and what a PC might want to be aware of.   I also mentioned that many people are writing new Vakaros visualization tools (and a PC should understand the settings of the tool being used).  Below is an opportunity to examine both these ideas.

One moment where we can assess that accuracy is when boats contact each other and leave visible damage.  Below is such an instance. This image comes from a screenshot from a new Vakaros viewing tool called mastabeam (Mastabeam.com). 

This is at a windward mark and the conditions were such that Green was heeled over with her rail close to the water.  As you can see, Pink's bow is overlayed on top of Green's rail.  That is a very precise representation of what actually occurred based on the evidence left behind.   

The collision occurred precisely there along Green's port side and down below Pink's bow peak such that her bow overlapped Green's rail.  

I've invited Kevin, the creator of MastaBeam to join this thread to offer insights he might have regarding Vakaros visualization in the context of PC hearings, since he's been working with these data streams. 

At Antigua Race Week 2024, a boat protested another boat for not rounding the mark on the correct side. The protestor was not close enough to observe the distance between the lead boat and the mark, but observed that the lead boat looked like it had to alter course, was close and upon review the tracker clearly showed that the lead boat had not rounded the mark on the correct side. 
Witnesses on the mark boat  were unanimously prepared to testify that the lead boat had rounded the mark on the correct side and it was not close to contact. The protest was withdrawn without a hearing. 

There are doubtless many similar stories as @angelo described in his example above.

Different GPS devices have different degrees of accuracy. In the surveying and civil engineering industry there are gps + accelerometer devices costing many thousands of dollars with high degrees of accuracy of under a meter. In defense and aerospace there are even more expensive devices with even higher degrees of accuracy. 

We describe GPS sensors in two ways, precision and accuracy.  Accuracy is the degree of closeness of the GPS estimated location to its true, but unknown location. Precision is the distribution of the estimated locations around the mean estimated location (ie the density of observations).  The two most common measures to define accuracy are:
1.  Circular Error Probability (CEP) .  CEP refers to a circle in which 50% of the values occur. If a CEP of 1 meter is quoted then 50% of observed horizontal point positions should be within 1 meter of the true position.
2. R95 or 2DRMS ( 2*Distance Root Mean Squared) This is a 95% probability circle where 95% of the observed horizontal point positions will fall within the specified diameter around the true position. 

There are two manufacturers of Electronic Race Management Systems (ERMS) which provide virtual start lines, race management software and tracking. Vakaros with Race Sense and Velocitek with Race Puck.  There are numerous manufacturers of nautical GPS devices that can provide post race tracking, ranging in price from $400 to $5,000. Any assessment of tracking data as evidence in a protest will have to take account of the accuracy of the device providing the data.

Neither Vakaros nor Velocitek build their own GPS sensors. They use readily available 3rd party sensors with published CEP and R95.  

The OP referred to Race Sense.  Vakaros provides two gps devices with a considerable difference in accuracy. The most commonly used device is the Atlas 2. This is a stand alone GPS device without a Real Time Kinetic (RTK) positioning base station. Based on analysis in other forums (I own an Atlas 2 but I have not pulled it apart to look at the sensors), the COP is around 1 meter and the R95 is 2.13 meters.  The second device made by Vakaros is called a Helio. This utilizes an RTK base station which improves the R95 to well under a meter. Vakaros has not published the data on any of their devices but their marketing materials refer to centimeters on the Helio. That seems optimistic but it is doable with RTK technology. 

Velocitek's Race Puck is solely based on RTK technology. At the time of writing they haven't published their COP or R95 results but they say they will. 

The Atlas 2 accuracy is very credible for using for start lines for most racers. A COP of 1 meter and R95 of 2 meters is plenty good enough for amateur racing.  The start line is relatively stable , reinforced in some cases by linking the base station with a positioning services like Swift Navigation's Skylark.  At something like Sail GP they use much more expensive systems with multiple sensors on the boat and RTK base stations on a fixed onshore position.  

However, if you allow race sense data, or any tracking data, in the protest room, you need to be very careful that you understand the compounding error effect of comparing the estimated positions of two gps plots. If the COP is 1 meter, then there is only a 25% probability that both boats are within 1 meter of the distance between the two boats defined by the gps plot. The outer edges of the two R95 circles can be anywhere from 2 meters to 4 meters apart.

Here are some guidelines that occur to me (just as a starting point)

1. The PC should not look at GPS tracking before hearing testimony from the two parties, and other witnesses. This prevents the approximate tracking from GPS creating any pre-testimony biases or coloring the judgement of the jury before they have heard from the parties.
2. Before allowing any submission of tracking data, the judges must know the accuracy of the GPS device and understand any latency in the subsequent tracking data. Preferably, someone on the panel should be suitably qualified  so that they can convert the temptingly looking line on the data into visualizing the wider band that it actually is. 
3. Before looking at the data,  I recommend defining the question you want to answer. For example, if you are looking to define whether a boat was on port or starboard, or whether it was previously coming from astern, or tacked to leeward. These are questions gps data may be able to help on. If you are looking for a point of time when an overlap was established , or how close to leeward a boat tacked to leebow, then you should probably not even open the data unless it is RTK enabled and even then you want to know the accuracy of the device.

We havent talked about how the frame of the boat is defined by gps or the direction it is pointing, which a simple stand alone gps will not provide because it measures course over ground and not the direction the bow is pointing.   

 I hope that helps frame the discussion. 

I would like to thank all of those who responded over the past 10 days to my post.  Clearly there is an interest in the system and we as Judges need to embrace it and be educated as to how best to use it.  Clearly there is a difference as to various systems, but what I am referring to currently is the Vakaros with Race Sense utilizing the Helio.  The J111, J24, J70, Melges 15 and J105 (and others) have been using it with success for the past few years.  As more and more events will be using this I feel that the Judges need to be educated as to it's functionality.
I see it used routinely in the protest room to settle differences between the Protestee and Protestor and it's use added to the Protest checklist.
In order to do this I will set up 2 Judges roundtables this winter, to educate those who have not worked with the system and to sharpen the understanding of the judges as to the use of the technology.  I hope to get some educational materials to be reviewed before the roundtable, and a judge like John Porter to lead the discussion.  
My thought is to have the Protestor/Protestee testify and then if the PC feels more information is needed then the Tracking information (prepared by the OA for viewing) presented.  If we are to use this data we need someone other than the PC/Parties to present it so as not to burden the PC with displaying technology they may not be familiar with.  Much of that will be up to the Judges Committee and they can discuss it at their annual meeting in February.
More people will be using it in the future and many classes have invested $6,00-$10,000 in technology to make this happen.  I think we as judges need to move forward with our customers providing good quality protest decisions.  Any suggestions please forward them to me.
Doc

Kevin here.  As Angelo mentioned I've been putting together a viewer for the data for our fleet, which I originally started to help some of us review and settle a mark room situation prior to needing to get into the room.  Given that there was a lot of thought about what the data can prove vs infer as we were looking at it together as adversarial parties not just trying to present a case in the best light.  There's a lot of good discussion here about GPS resolution/accuracy I won't rehash so I'll try to stick to some key points I don't think have been considered yet:

1.  Boat motion in the Vakaros RaceSense player is interpolated.  If you're simply viewing the RaceSense player that means from one GPS logged position to the next (each having heel, heading, SOG, COG) the motion, turning, and position of the boat is assumed to have a perfectly smooth transition between the two points.  It is entirely possible for a boat to duck another one, then come back up on the other side and if the mesh network didn't manage to get data over to the tablet during those critical seconds the player might show the boat traveling in a straight line right through the other boat.  As far as I know the player does not have an ability to only show only the logged GPS points which means you're not just watching something with GPS inaccuracy, you're watching smoothed motion between two points with GPS inaccuracy which may in actuality be a complete large gap in the record.  This can contribute to where you're seeing boats moving sideways.  It's not that they knocked their atlas device on the mast, it's that you're looking at a 9 second data gap where a tack occurred in the middle of it so the track is showing the boat moving directly towards the new point but it's smoothing the heading change for the boat across all 9 seconds of the gap.  Here's exactly such a case:

If you pull the data, what you really see is a data point where the 90 degree turn is with them on the original tack and then 9 seconds later a new data point way to the right fully on the new tack.  All the sideways sailing is from the interpolation, there's no actual Heading or COG readings for what it's displaying for those 9 seconds, just the delta divided over the time for smooth display.

This is not a knock on Vakaros player.  Watching tracks without interpolation on makes me want to stroke out from all the jittering and they weren't intending it to be used for determining protests so it's perfectly reasonable to have interpolation on for it.

But it's a real limitation if you ARE trying to do that.  To help us deal with this I included a toggle on our viewer so that you can turn interpolation off for situations where you need to see the actual evidence in it's sparse form without anything filled in for you.  When interpolation is off each boat shows a timer indicating how stale the GPS data point is in relation to the player time. A positive number like 0.5s means the data point is stale by .5s and a negative number means it's from the future which now that I type up is probably going to confuse people and should be inverted.  Anyways, the point is, you need to know if the closest data point is older or in the future of the current player time and what that time delta is compared to the other boats to actually evaluate data that actually exists. Below you can see the view with interpolation off for some boats doing a mark rounding so you can see where we've paused the player is 0.2 seconds ahead of the closest GPS data points for the boats.

2. The main problem with (1) stems from RaceSense data being sparse due to the limited bandwidth of the mesh network and distance compounded by distance from RC.  But it doesn't have to be, high fidelity data is stored in each competitor's Atlas 2 device.  In the screeenshot above you'll notice the non-interpolated data shows extremely narrow deltas (.2s). That's because we didn't only use the RaceSense data that has sparse capture via the on the water mesh network, we each uploaded the VKX export from the session using the Vakaros Connect App.  That fills it in with data points every quarter second whether you're in range of RC tablet or not.  Getting that data though requires the competitor's Corinthian spirit in actually finding the truth so likelihood of that might differ between classes/events.  Personally though as a competitor, if we're participating in an event where we are required to have a working atlas 2 to as part of the rules and it's automatically calling OCS for us, I don't see why we shouldn't be also required to provide the non-sparse track data when requested for a hearing in the event.


How we've used the data so far:

Ignoring performance analysis, for the purposes of protests we've used it to evaluate our on the water judgement calls and come to agreements with the adversarial boats and avoid the room.  In other cases the data showed there was still uncertainty and it continued to the room.  Both I believe are valid outcomes and it required the different parties talking to each other and changing parameters to help make sense of the situation.  In this particular case it was a rounding of a government mark so there's not an atlas 2 device recoding it's true position at the moment of rounding.  So we started with some accepted facts like no one sailed on the wrong side of the mark or hit it, so the mark must be within the turning track of the three boats.  Then we have some reasonableness judgements like "this boat rounded tightly to the mark and they didn't sail past it 20m so we'll try out different mark locations within the bounds of "reasonableness" and see if any change the result of overlap and/or entrance order.  It helped us eliminate reasonable possibilities which is an important distinction between "we looked at it and it gave us the answer which we blindly accepted"  For example, it checks the overlap at all paired (closest time) GPS points in a 2s window in addition to the reading at the moment of entry.  This, along with visual display of how big the overlap was, can help give (or rightfully undermine) confidence in the at the moment of entry determination.

This all goes back to what's running at the core of this conversation though.  Track data is evidence the same way witness testimony is evidence.  I'd say it's wildly better at estimating distances even on a bad day  (I routinely hear people call the 3-boat length circle while there are literally four physical boats in a line between them and the mark) but it still need to be understood to be fallible and thus questions need to be asked like "if the recorded heading is off by 10 degrees or time of entry into the circle is different by a second in either direction does it reasonably change the result?".

There's still uncertainty, but it helps eliminate a lot of possibilities.

@ Angelo, I hope you had an exhilarating spin class. I look forward to your new thread on admissibility of gps data. I will have one general question, and one observation.

The question (and I genuinely dont know the answer) is :  If I call a witness for a protest, can they decline to attend the protest meeting? 

The observation is that I have been in a race where we are required to carry a tracking device (yellowbrick) and the NOR states that everyone's position is reported and shared simultaneously every four hours. It was clearly stated that it would be a breach to disable or turn off the tracker prior to and during the 4 hourly  "check in" .  Thus, in effect the NOR required sharing GPS data. 

As an aside , it had the fun (and intended) effect that if we saw a good reason to gybe 20 minutes before the check in, we would hold off for 20 minutes, then gybe and get a 4 hour jump while we were "dark" before anyone could cover us. It turns out that trans ocean racing can be almost as much fun as racing dinghies on the River Crouch.  :)

In response to Kevin. I do not think that there are many. PC that have the knowledge or ability to show and manipulate the player to show what we want to see which is why I would add to the OA responsibility someone to manipulate the player  often that might be one of the juniors as they spend so much time on their devices anyway