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Old 28-11-2015, 11:15   #1
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Do we need/want an AIS filter?

I'm playing with the idea of coding an AIS filter. Special in crowded areas the screen can be to clogged to be usefull.
Filtering could be done for CPA, TCPA, class B, class A .......
The filtered targets could be still visible but smaller, transparent or without AISname.
A warning should be onscreen, something like is used for "overzoom".
Maybe there should be a timer that switches off the filter after a certain amount of time.

What are the thoughts here about this, as I do understand there could be some resistance against filtering. (and maybe with very good arguments)
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Old 28-11-2015, 11:19   #2
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Re: Do we need/want an AIS filter?

Aren't filters already built into AIS units?
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Old 28-11-2015, 11:50   #3
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Re: Do we need/want an AIS filter?

Quote:
Originally Posted by Stu Jackson View Post
Aren't filters already built into AIS units?
No, AIS receivers / transponders do not do any filtering. All received AIS messages get sent to the chartplotter (OpenCPN, etc).

Some chartplotters will do filtering based on target speed, status, etc. Mostly, filtering is to set alarm parameters, not change the target display. If the chartplotter is being used as a multiplexer, passing along AIS messages with other NMEA data, all AIS messages will be forwarded.
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Old 28-11-2015, 12:06   #4
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Re: Do we need/want an AIS filter?

It will take a very very smart algorithm to outsmart life.

Are in la Manche. Malacca, Gibraltar?

b.
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Old 28-11-2015, 12:12   #5
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Re: Do we need/want an AIS filter?

And to remember: there are filter for alarms in the AIS settings.

Not for targets = ships with AIS transponders in range (range is the only parameter in the AIS list)

These are two different concepts which might intersect: a non-visible (= filtered target) can trigger an alarm for example.

I understand the wish for filtering to avoid clutter but on the other hand I feel very uncomfortable to make a possible hazard or object vanishing.

Scenarios and parameters which serve to discuss pros and cons?
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Old 28-11-2015, 12:20   #6
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Re: Do we need/want an AIS filter?

My first thoughts are, make the targets smaller or semi transparent (or both) but don't let them disappear completely.
Also removing the name on small scale and/or not showing a speed vector could help.
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Old 28-11-2015, 12:23   #7
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Re: Do we need/want an AIS filter?

On our Furuno ecdis at work it has filtering for no active targets. Such as vessels with activity designation of moored or stationary. So you won't see vessels at the dock not moving. We don't have many vessels anchor in/near our Port (most vessels are tied up, on DP, or smaller ones shoved in the mud) so I don't know how it works.

Also, we don't use filtering on our unit.

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Old 28-11-2015, 12:27   #8
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Re: Do we need/want an AIS filter?

Scale?

On 1:1.000.000 you can get ports or zones of high traffic covered by targets - but is this a problem as it does not have any impact on awareness or alerts? The Vesselfinder or Marinetraffic view when zooming out...

So one more parameter.

With respect to filters on ECDIS units it seems to me that those can filter visibility - the famous Class B filtering debate - but this does not imply to disable alerts.

When does visual clustering really bother?
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Old 28-11-2015, 12:32   #9
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Re: Do we need/want an AIS filter?

The Vesper Vision AIS does exactly what you describe for its own display, but forwards unfiltered date to OPCN. After a few months of usage, I'm somewhat ambivalent about the concept as presented. The discarded targets (unfiltered in Vesper parlance) are perhaps too transparent and small for my old eyes and I sometimes miss seeing them. However, if they exceed any of the alarm parameters that you have set, they become larger and red in colour, and of course, an alarm is sounded.

The vesper display is much smaller than our computer screens, and I understand that it might become uselessly congested if some such scheme was not used. I'm not so sure that such is necessary on the computer. If running OPCN on some smaller device, I see the usefulness.

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Old 28-11-2015, 13:00   #10
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Re: Do we need/want an AIS filter?

One could just imagine the field day the lawyers would have against the software developer if a filtered target (probably illegal under colregs) hits a boat and kills a few babies.
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Old 28-11-2015, 13:36   #11
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Re: Do we need/want an AIS filter?

OK, I will try to make a little more concrete.
Maybe not the best example, but the only one I have available. (see picture)
If this was an unknown port, the AIS targets would be of zero help. Even worse it hard to see where is water
So I think of something like a point system.
Speed less then 1 knot -> 2 point
Speed less then 2 knot -> 1 point
CPA more then 10 NM -> 5 points
...
CPA more then 1 NM -> 1 point
class B -> 1 point
TCPA -> 30 min 5 points
....
TCPA -> 5 min 1 points
Then total the points. If more then 1 point size of target 80 %
2 points size of target reducet till 60%
3points size 40%
4 points size 40% and transparence 20 %
5 points size 40% and transparence 40 %
6 points size 40% and transparence 60 %

Where the point scale for CPA and TCPA maybe should depend of the chart-scale used.
So I DON'T intend to let targets disappear completely, just make the underlaying chart more visible.
Also it could be an idea to start filtering only when more then 30 targets onscreen.
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Old 28-11-2015, 15:34   #12
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Re: Do we need/want an AIS filter?

I had to deal with AIS cluttered charts when I passed through the Strait of Gilbraltar about 10 years ago (AIS Target Filter in SOB).

I found that zooming to a chart scale useful for detailed navigation, such as entering a harbor, and minimizing the AIS info displayed eliminated the clutter problem for my needs. The filtering I still needed was for the display of dangerous targets to eliminate the flagging of stationary targets. Digiboat fixed this issue for me as described above. OpenCPN and most other AIS display packages have the same capability.

The filters proposed by the OP sounds neat, but maybe a little too complicated to be practical. For me, if the AIS chart clutter is too severe when zoomed to the necessary chart scale, then I would just turn off the AIS display.

However, I might change my mind when I had the chance to actually use the proposed filter. So I wouldn't want to discourage the development of capability, it's just not something I feel a burning need for.

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Old 29-11-2015, 14:50   #13
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Re: Do we need/want an AIS filter?

RooieDirk

There is a rather large list of AIS Feature Requests in Tracker. It is probably worth reading them to see if there are some other techniques which would be useful.

OpenCPN::Tracker 00 - OpenCPN - Feature Requests: Tasklist

I will try to put them into several additional categories such as
AIS alarm, AIS visual, AIS filter etc. to make it more manageable.

How to make the display more meaningful for "contacts" of concern and how to reduce the presence of other contacts that are not of concern.

How to control alarms which are least likely to occur, which happen due to course changes under heavy seas, so far distant /in the future (time & distance) that it is not worth changing course yet, etc.

The tracker AIS items are not a bad place to start for additional ideas to help this interface, because most of them are coming from active users of AIS.

Your sea experience should also be an assurance to others about your understanding of the issues. Thank you for taking this up, it would be a big assist.
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Old 29-11-2015, 15:48   #14
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Re: Do we need/want an AIS filter?

Alarm settings ideas
1. Proximity FS #1881 - Establish a guard zone (distance) as in radar. Include a time element guard zone.
2. Reduce nuisance alerts FS#807 - Add damping factor adjustible seconds of continued alert conditions before the alert sounds
3. AIS Alarm acknowledge shortcut FS#1260 Provide a shortcut key + left mouse to close one or all Acknowledge alerts that are outstanding.
4. Temporarily Disable Alarms FS#1573 - Provide an Icon Button toggle to temporary stop all acknowlege alerts. Provide audible alarm instead (option)
5. Small AIS enhancements FS #668 - See #5

Alarm Clutter ideas
1. Suppress CPA calc for boats at anchor FS #1826
2. Make Make targets user definable FS #668

Permanent Disable for certain types
FS 1884 AIS Remember "white" list - fleet, disable alarm, proximity - Similar to Vesper.
Hakan implemented "Follower" class which disables alarms.

It would be nice to have some of these AIS tasks be closed, but the community should inform rooiedirk's effort. So please speak up if something appears to be headed in the wrong direction.

(Perhaps some have already been executed!!! -- if someone notices this please advise.)
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Old 29-11-2015, 15:58   #15
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Re: Do we need/want an AIS filter?

s/v Sarah, thank you for
AIS Target Filter in SOB
-- Contacts not underway are not a threat.
-- Contacts anchored are not a threat.
-- Contacts with SOG less than X are not a threat.
-- Ignore Stationary filter (third from the bottom on the right side of the screen) to a value of 1.0 kts. +++ So I verified that SOB will not flag targets as dangerous if their Speed Over Ground (SOG) is less than the value set in the filter control. I also verified that targets moving faster than the control setting will still be flagged as dangerous if they are projected to come within the safe distance specified.


So, lets keep it simple Please, and figure out what needs to be implemented.
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