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Old 29-01-2014, 06:24   #46
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Re: AIS Class B targets

Still not seeing it. All of the AIS devices that I am aware of are smart enough that their alarms are based on distance and rate of closure. Hence, a faster moving target is going to alarm at a different distance than a slower moving target anyway. The size of the target vessel really shouldn't make any difference. You don't want to collide with a 60' pleasure yacht that is moving at 20 knots anymore than you want to collide with a 600' cargo ship that is moving at 20 knots.

Keep your eyes open, maintain a proper watch, use the AIS as a backup and an aid, not your primary lookout device, and none of this is a problem.
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Old 29-01-2014, 06:54   #47
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Re: AIS Class B targets

denverd0n,

I would propose to remove the alarms from the screen, they make a mess of it.
If OpenCPN is able to generate XTE and/or RMB messages based on the AIS-A and AIS-B alarms, my autopilot can do the work and I can stay in my bed. This is innovation! Not?
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Old 29-01-2014, 08:09   #48
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Re: AIS Class B targets

The RTIR is a specific issue - 1800 boats trying to cross a start line in 200 boat groups 10 minutes apart and I think falls into Pavel's category of 'unique situations that are not worth filtering.

I was trying to describe a more common situation where (for instance) on many a Saturday or Sunday morning Sunsail (or Britania) have 25 40ft yachts messing around (sorry I mean manoeuvring) on top of Spit bank for a start-line. These boats do 7 to 9 knots and their CPA calculations mean you get 30+ red lines whipping all over the display (25 for Sunsail, the hovercraft, car ferry passenger ferry, Gosport ferry, Condor cross channel ferry the odd pilot boat and a couple of banannananana boats leaving Portsmouth harbour. This is in addition to any other yachts with Class B AIS transponders and any shipping trundling along the Solent to or from Southampton's container port or the Fawley Oil refinery.

In this situation I want to see the tankers, ferrys, dredgers and tugs but not the yachts.

I'll find a download of a day like this - once the season gets going again

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Originally Posted by bcn View Post
We got a nicely crowded solent - courtesy of em-trak, thanks.

Pavel can play now a bit more I hope....


Hubert

if somebody else wants the file for playing, please drop me a mail at info@o-charts.org
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Old 29-01-2014, 08:58   #49
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Re: AIS Class B targets

roundm,

your scenario is well understood - issue is getting an appropiate data set.
The RTIR at least increases the "population density" to test approaches.

Hubert
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Old 29-01-2014, 09:03   #50
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Re: AIS Class B targets

If somebody wants to run an AIS stress test on his Windows machine, here is a data set which shows nearly 11.000 vessels:

http://www.aishub.net/downloads/nmea-sample.zip

My newest Win8 PC will survive the test, the W7 gets very sloppy at the end and the XP seems to stall - at least I didn't had the pacience to wait an hour more.
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Old 29-01-2014, 09:59   #51
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Re: AIS Class B targets

Quote:
Originally Posted by denverd0n View Post
Keep your eyes open, maintain a proper watch, use the AIS as a backup and an aid, not your primary lookout device, and none of this is a problem.


I agree! The solution to having a mess of AIS targets cluttering the screen is to either not look at the screen or turn your AIS transceiver OFF!

I'm waiting for the first accident investigation where the helmsman claims the reason for the collision is because the vessel wasn't on his AIS display!!!
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Old 29-01-2014, 10:01   #52
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Re: AIS Class B targets

Quote:
Originally Posted by bcn View Post
If somebody wants to run an AIS stress test on his Windows machine, here is a data set which shows nearly 11.000 vessels:

http://www.aishub.net/downloads/nmea-sample.zip

My newest Win8 PC will survive the test, the W7 gets very sloppy at the end and the XP seems to stall - at least I didn't had the pacience to wait an hour more.
No problem with MacBookPro late 2009, however nearly 30% CPU usage.

Gerhard
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Old 29-01-2014, 10:34   #53
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Re: AIS Class B targets

Hubert

I didn't want to be disregarded as raising 'silly' suggestions. This is obviously a topic that raises a number of comments from people who have not experienced the problem. on the RTIR I really feel sorry for the commercial guys - I've seen the hovercraft sit still for 15 minutes looking for a gap in the traffic (amazing skills from the skipper/pilot I have to say!)

To denverd0n it's not an issue around keeping a lookout, it's that one of the tools we have at our disposal (AIS), that can help us interpret the situation becomes useless in some circumstances. That is what we are trying to show and improve.

Coming out of Cowes on the RTIR, during Cowes Week or on many other weekends in the summer is a manic experience apart from anything in amongst all those triangles are the 40knot Red Jet (although not doing 40knots on that particular day) and the Red Funnel car ferry! I really feel for their skippers. The yachts will all be manoeuvring for the start and the CPA alarm just needs to be switched off for them - what we could do with is an alarm reminding of the tanker steaming up behind us and through the middle of the start line though.

The Solent is an oddity, I just looked at the keelboat events that are planned and are registered with the SCRA and even in Jan there are a fair few - but looking at May (as a for instance) there are 78 events in the month - and 9 races on a single day! (17th May). Increasing numbers of these events are using AIS to track competitors and the boats are not following channels or navigating normally.The complexity of their movements can hide the real shipping. This is the sort of 'normality' that sailing in this area results in (it is fun though - there are frequently beautiful and spectacular boats around).

incase you are interested
Solent Cruising and Racing Association - Search by date

it's dealing with the fallout from these events that I'm raising - whilst the fleets doing 8 knots will be spotted by the mk1 eyeball all their AIS tracks effectively hide the tanker doing 15knots in their midst - The yachts triggering alarms hides the alarm I really want to know about because the tanker is doing something unusual and unpredicted (heading for a different channel, changing heading because of something he's seen and I'm not affected by or something similar).

Portsmouth harbour entrance is also a special case - I always say if you leave Portsmouth harbour and haven't seen 5 ferries - you weren't keeping a decent lookout cos you have missed some. The sheer numbers of yachts confuse the issue and prevent meaningful AIS alarms to be set.

I will try and find a source of NMEA data that shows this this - I've loaded the file from San Francisco and whilst there is a pinchpoint, there are not enough boats around for long enough to show the level of confusion much.

and thanks for a fantastic tool - apart from calculating tidal course to steer OpenCPN provides just about every function you could want.

Mark



Quote:
Originally Posted by bcn View Post
roundm,

your scenario is well understood - issue is getting an appropriate data set.
The RTIR at least increases the "population density" to test approaches.

Hubert
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Old 29-01-2014, 14:21   #54
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Re: AIS Class B targets

Quote:
Originally Posted by roundm View Post
Hubert

I didn't want to be disregarded as raising 'silly' suggestions. This is obviously a topic that raises a number of comments from people who have not experienced the problem. on the RTIR I really feel sorry for the commercial guys - I've seen the hovercraft sit still for 15 minutes looking for a gap in the traffic (amazing skills from the skipper/pilot I have to say!)

To denverd0n it's not an issue around keeping a lookout, it's that one of the tools we have at our disposal (AIS), that can help us interpret the situation becomes useless in some circumstances. That is what we are trying to show and improve.
Mark
Mark, exactly that's why your comments are helpful:

how to improve the tool AIS:
How to implement setting priorities - that's what we are doing when we are looking at the overcrowded display (or through the window).

How can we define groups or single vessels to be put into the "background"?
How to define a "behavior" that makes you to ignore or to have a sharp outlook for a target?
Areas?
Mark them one by one - ignore or keep especially watch? And if one behaves different - "strange" as your sixth sense or experience would tell you? How to define this?

Your play ground is for sure a very challenging one - and have a look at the Med in the morning where more and more fishing vessels are showing AIS now.

Interesting challenge.

Hubert
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Old 30-01-2014, 06:42   #55
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Re: AIS Class B targets

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Originally Posted by roundm View Post
...whilst the fleets doing 8 knots will be spotted by the mk1 eyeball all their AIS tracks effectively hide the tanker doing 15knots in their midst...
I think you need to re-read what you wrote here, and think about it some.

You can look out and see the fleet, but you can't see the giant, looming, ten-times-as-tall tanker in their midst? The AIS tracks are hiding that from your mk1 eyeball? Come on.
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Old 30-01-2014, 07:23   #56
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Re: AIS Class B targets

Our newly fitted Garmin AIS600 transponder has a 'transmit off' switch fitted (an extra easily added) so that we can turn ours off to avoid adding to clutter in inshore waters or to be invisible to anyone with possible malicious intent in mind like pirates or potential robbers in 'dodgy' areas

I haveto add that folk over here in the USA do not see the kind of target clutter common for example around the Solent in the UK so perhaps do not fully understand some of the comments made. Sure the mark 1 eyeball should always be the deciding factor but again in some waters the visibility can be bad or deteriorate fast, imagine the two screen shots posted above in a thick fog situation.

Here in our marina we get AIS alarms as soon as we switch on, just from 24/7 transmitters on adjacent docks. Why do people leave their AIS transmit turned on when they have obviously gone home, is it just paranoia about the boat being stolen so they can look ononline at home and see their toy is still safe in it's slip?
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Old 30-01-2014, 08:10   #57
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Re: AIS Class B targets

Quote:
Originally Posted by denverd0n View Post
I think you need to re-read what you wrote here, and think about it some.

You can look out and see the fleet, but you can't see the giant, looming, ten-times-as-tall tanker in their midst? The AIS tracks are hiding that from your mk1 eyeball? Come on.
No one is saying that they want to sleep whilst crossing a busy traffic zone and let AIS deal with keeping watch. The suggestion is that more maneuverable vessels with unpredictable course changes don't warrant an alert because it just generates mindless never ending beeping. However, the less maneuverable vessels on a near collision course must create an alert that is not drowned out by the noise. In many situations smart filtering is the only way to keep the thing from bleeping all the time and painting the screen solid with projected tracks. In comparison, our brain automatically filters even though we don't think of it as such. We automatically filter out the vessels not likely to cause trouble while focusing on the ones we think may be problems. If a computer could be taught the same intelligent filtering techniques it would improve safety because they don't get lazy or become distracted with other tasks. For many of us who use and like OCPN it would be much appreciated. If you don't want to use AIS that's fine but I don't see why that precludes others from trying to improve on it by making suggestions.

I don't think filtering out class B is the answer. But there are no doubt algorithms that could be proposed that would make AIS much better in crowded areas. Intelligent filtering is going to be required if AIS is to help avoid collisions in places where they are most likely. Without good filtering it will be turned off and of little use at all.
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Old 30-01-2014, 08:59   #58
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Re: AIS Class B targets

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The suggestion is that more maneuverable vessels with unpredictable course changes don't warrant an alert...
Not buyin' it. If any target warrants an alert then any target that you might collide with must warrant an alert. And just because a target is making unpredictable course changes doesn't mean that you can't collide with it. In fact, that probably makes it MORE likely that you could collide with it!

I guess here's the problem that I have with the whole discussion. It seems that people want to use AIS to help them avoid collisions. I see that use of AIS as fundamentally flawed. AIS is not supposed to help you avoid collisions. What it is supposed to do is help you to identify situations where you should then use your eyes to help you avoid collisions. I know that sounds like a nit-picking difference, but it is not. The function of AIS is simply to help make you aware. Once aware, it is up to you to look out and figure out how to avoid a collision.

In the circumstances being described here, you should already be aware. You should already be looking out. Hence, AIS cannot help you here. It serves no real purpose in this particular circumstance. You have already been alerted. When you're in close proximity to a large fleet of boats that are maneuvering unpredictably, you should be keeping your eyes out and your head on a swivel. You shouldn't be looking at your AIS at all!

And if you are keeping your eyes out and your head on a swivel, then obviously you are not going to miss some giant tanker bearing down on you.

With that I will let it go. Someone else is welcome to have the last word.
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Old 30-01-2014, 10:37   #59
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Re: AIS Class B targets

Quote:
Originally Posted by denverd0n View Post
Not buyin' it. If any target warrants an alert then any target that you might collide with must warrant an alert. And just because a target is making unpredictable course changes doesn't mean that you can't collide with it. In fact, that probably makes it MORE likely that you could collide with it!

I guess here's the problem that I have with the whole discussion. It seems that people want to use AIS to help them avoid collisions. I see that use of AIS as fundamentally flawed. AIS is not supposed to help you avoid collisions. What it is supposed to do is help you to identify situations where you should then use your eyes to help you avoid collisions. I know that sounds like a nit-picking difference, but it is not. The function of AIS is simply to help make you aware. Once aware, it is up to you to look out and figure out how to avoid a collision.

In the circumstances being described here, you should already be aware. You should already be looking out. Hence, AIS cannot help you here. It serves no real purpose in this particular circumstance. You have already been alerted. When you're in close proximity to a large fleet of boats that are maneuvering unpredictably, you should be keeping your eyes out and your head on a swivel. You shouldn't be looking at your AIS at all!

And if you are keeping your eyes out and your head on a swivel, then obviously you are not going to miss some giant tanker bearing down on you.

With that I will let it go. Someone else is welcome to have the last word.
I kinda have to agree with you. Partially. Well, mostly.

If there are too many alerts to process, then I have to accept that the current situation is just too complex for the software to handle. It is one of those comforting times when I can feel like I am still smarter than my computer. I need to turn off all alerts and rely on eyes. And get another person or two up on deck for added lookout. And slow down. And... you get the idea, I am in a touchy situation that demands sharper lookout than normal.

On the other hand, I think it is valuable to have discussions on ways to make the software more intelligent so maybe a way could be found to add some modifications/filters/modes that help rather than obscure.

FWIW: I personally do not think filtering out class B is the answer.

-dan
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Old 30-01-2014, 11:39   #60
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Quote:
Originally Posted by denverd0n View Post
Not buyin' it. If any target warrants an alert then any target that you might collide with must warrant an alert. And just because a target is making unpredictable course changes doesn't mean that you can't collide with it. In fact, that probably makes it MORE likely that you could collide with it!

I guess here's the problem that I have with the whole discussion. It seems that people want to use AIS to help them avoid collisions. I see that use of AIS as fundamentally flawed. AIS is not supposed to help you avoid collisions. What it is supposed to do is help you to identify situations where you should then use your eyes to help you avoid collisions. I know that sounds like a nit-picking difference, but it is not. The function of AIS is simply to help make you aware. Once aware, it is up to you to look out and figure out how to avoid a collision.

In the circumstances being described here, you should already be aware. You should already be looking out. Hence, AIS cannot help you here. It serves no real purpose in this particular circumstance. You have already been alerted. When you're in close proximity to a large fleet of boats that are maneuvering unpredictably, you should be keeping your eyes out and your head on a swivel. You shouldn't be looking at your AIS at all!

And if you are keeping your eyes out and your head on a swivel, then obviously you are not going to miss some giant tanker bearing down on you.

With that I will let it go. Someone else is welcome to have the last word.
This is an over simplification of the issue. Firstly AIS has collusion alerting features ( or rather the MFD has). This collision feature is exactly the same as ARPA collision warning features.

Both of these are useful when you can't immediately see the AIS or radar screen. Equally they serve to automate having to do manual radar plots to determine CPA

I find exactly the same problem with lots of ARPA targets. The alarms have to be silenced.

The same is true of busy AIS B data triggering collision alarms. These yachts generally are not the problem and will tack out of the way. The big ship is the problem and it may not be obvious where to go to avoid it.

There definitely needs to be better filtering on class B targets to allow finer discrimination.

Some MFDs have very poor options on that regard


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