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Old 30-06-2013, 04:38   #1
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AIS Class B targets

The AIS situation around Stockholm this morning....
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Where are the real important targets......? Is there a tanker in there heading my way?
It would be nice with an option, with a shortcut, to switch Class B targets on/off.
What do you think?

Thomas
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Old 30-06-2013, 05:08   #2
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Re: AIS Class B targets

Ships dont filter Class B out. It would be suicidally crazy for us to start a revolution that leads to ships filtering us.

I cant enlarge the screen shot. Why are thereso many targets? Warm weekend afternoon? Well thats only a few days per year.
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Old 30-06-2013, 05:29   #3
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Re: AIS Class B targets

Mark

Digging into some local Stockholm newspapers on the net, it looks like a race with some 300 boats starting, so it's not an everyday situation.

I'm not suggesting that ships should filter out Class B targets, for the simple reason that OpenCPN can never be legally used as an ECDIS.
This is more along the lines of a Class B target temporarily filtering other Class B targets to be able to distinguish Class A targets.

Thomas
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Old 30-06-2013, 05:46   #4
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Re: AIS Class B targets

cagney, et al...

I support this idea.

In real life, close-aboard encounters with Class B targets in inshore waters can be confusing. This is mostly due to the slow reporting rate for Class B. What you see on the OCPN screen is nothing like the real situation. Fast Class B targets may be over the horizon before their next report. Couple this with the often poor antenna placement and low transmit power of most Class B vessels, and you end up with nonsense on the display. Lots of static, expiring targets in the wrong place.

I think many Class B vessels would be surprised to discover how very short is their transmit range. Depending on antenna placement and relative ship orientations, it may be only a couple of miles.

I have about come to the conclusion that Class B is great for helping ships avoid yachts when offshore, but nearly useless in helping us avoid each other in typical inshore situations.

But that's just my opinion.

Dave
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Old 30-06-2013, 06:08   #5
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Re: AIS Class B targets

How about using transparency for filtered targets? The filtered target will still be visible with the same color coding but be easy to tell from unfiltered targets.

Filters (for example) could be :

- Class A (all)
- Class A (CPA greater then X)
- Class B (all)
- Class B (CPA greater then X)

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Old 30-06-2013, 06:58   #6
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Re: AIS Class B targets

AIS can frequently track 200+ targets in the greater NY area on any given day. You can't rely on it solely, but any large traffic would be be on 13/16 with that much going on. You can also snoop on the Stockholm VTS (channel 73) just don't broadcast unless you're in the system.
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Old 30-06-2013, 07:18   #7
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Re: AIS Class B targets

Oh, no, too many idiots transmitting. There was a thread recently that discussed the "concept" of "overdoing a good thing."

The other issue is basically "what's the time frame of the screen shot?"
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Old 30-06-2013, 07:45   #8
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Re: AIS Class B targets

Why do you call them idiots for transmitting? They all seem to be actively underway and navigating. Isn't that the whole idea of an AIS transponder?

Mark
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Old 30-06-2013, 08:38   #9
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Re: AIS Class B targets

I agree. Why call them idiots for transmitting?

And when theres 300 boats coming towards you then I bet your eyes are peeled and when you see a wall of steel a thousand times bigger than one of those yachts you will notice its a ship.
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Old 30-06-2013, 09:22   #10
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Re: AIS Class B targets

Looking into what was, and is, going on, it shows that the " Sailing Instructions Ato 2013 " mandated the use of AIS for all participating yachts.
Quote:
1.8 All boats must be equipped with AIS and have it turned on during the race.
See this link for more http://www.google.com/url?sa=t&rct=j...K3_GUGeggJZD4g

So this is what we can expect in the future, and it would be nice if OpenCPN could help in the decision making.
The outstanding thing with AIS, in waterways like the Stockholm archipelago, is the ability to know what targets are hiding behind the next headland or narrows.

Thomas
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Old 02-07-2013, 11:03   #11
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Re: AIS Class B targets

Indeed some de-cluttering sometimes may be necessary, but plain filtering out Class B seems unfair ... Maybe just enhance the display/warning/alarm system instead?

Much more often than Class B one encounters problems with dense Class A traffic ... When entering a busy harbour shorthanded, fiddling with many filter/alarm settings, etc. is quite distracting.

So, just filtering out Class B will help only in very few cases. Also, quite large vessels carry Class B transponders - I do not want 300 tons filtered out with all the small boats. On the other hand, more and more yachts around 20m LOA carry Class A.

Some interim measures could be taken to show a lighter icon for these presumably smaller vessels ( some time ago I experimented with a smaller size ). Many nav programs show Class B as tiny circle, but I never got used to that, since it just does not _look_ like a ship. However, the main thinking should be about coping with AIS congestion in general, not just Class B.

What one might do (just thinking aloud)?

- limit the range of displayed targets (already available in the target list, but not on the chart)

- limit the warnings/alarms per CPA/TCPA (already available, but perhaps specify limits per vessel size <24m | >24m, or at least per-Class, not one-limit-for-all)

- reduce the work needed to handle the alarms ( 1. allow manual acknowledge by any keypress, without delicate mouse pointing; 2. optionally set automatic acknowledgement after 1-2-3... alarm rings, so no need to go below to handle the keyboard )

- make the icons reflect actual size of the vessel (already available? but maybe progressively drop the smaller ones from display as one zooms out, stepping through COLREGS ranges 7m-12m, 24m, 50m, 100+m, or select minimum size to show in the Target List dialog).

- show very condensed Dangerous Target list only, sorted by CPA/TCPA, with ability to display on chart just selected/dangerous targets (probably this is most important, and this is what big ships have).

By example, Furuno ECDIS allows quite flexible filtering/alarm strategies (attached), but next to it sits an MKD device, where no filtering is allowed at all, just switching between All/DangerousOnly target lists. OCPN operators usually have no MKD nearby...

It also might be, that in extreme cases AIS needs a separate screen, and a separate person to handle it ...
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Old 04-07-2013, 02:15   #12
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Re: AIS Class B targets

Quote:
Originally Posted by PjotrC View Post
- show very condensed Dangerous Target list only, sorted by CPA/TCPA, with ability to display on chart just selected/dangerous targets (probably this is most important, and this is what big ships have).
That would be my preference.

Reducing range or size of vessels displayed increases the risk from fast moving and/or smaller targets. Being hit broadside by a jet ski at 30 knots is gonna hurt. Not that jet skis carry AIS transponders but you get the idea.........
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Old 04-07-2013, 04:01   #13
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Re: AIS Class B targets

If each AIS target was awarded a THREAT SCORE based on a number of criteria, then the user could select the threat score they want to display at any given moment.

For example the threat score could be the addition of:

CLASS Score
A 5
B 1
AtN 9
SAR 9
AISSART 9
BASE 9

LOA
<20m 1
20-50m 2
50-80m 3
>80m 5

SPEED
Anchor/Moor 1
<2 kts 1
2-14 kts 2
14-23 kts 4
>23 kts 5

TYPE
36,37 (pleasure/sail) 1
...
51 (sar) 9


Example

a Class B, at anchor, <20m, sailing vessel gets a threat score
1 + 1 + 1 + 1 = 4

a class A tanker >100m doing 24 kts gets a threat score
5 + 5 + 5 + 5 = 20

I then use a slider on my display to indicate what threat score I want to see - this could even be dynamic depending on my speed/conditions.
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Old 04-07-2013, 23:36   #14
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Re: AIS Class B targets

Take a look at the target prioritisation techniques used in the Vesper Watchmate series of AIS receivers, displays and transponders for an elegant way of handling this issue.
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Old 05-07-2013, 02:22   #15
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Re: AIS Class B targets

It would be great if you might add some examples/screenshots and /or a link to the manuals in order to have a look what can be improved on top of the already existing options.


Some thoughts about this issue:

- the situation Thomas documented is an extreme one and if you are in a narrow channel with 200 race boats you will be eye ball navigating anyhow (or stop and wait)

- cluttering from AIS targets happens usually when zoomed out. I remember situations of that type at the port of Barcelona or in the bay of Palma de Mallorca. But then with a zoom level I would not use for navigation in that moment.

- personally I don't like the idea of filtering targets or objects. Later you forget about it and one may bite you...


What would be handy for this type of situations are several panels or viewports each with it's own settings and filterings to cope with the personal preferences . I'm not talking about running various instances of OpenCPN simultaneously.

Hubert
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